Atmospheric Environment (v.152, #C)
Editorial board (i).
Levoglucosan on Tibetan glaciers under different atmospheric circulations by Chao You; Tandong Yao; Chao Xu; Lili Song (1-5).
Tibetan glaciers are natural documents of the specific biomass burning biomarker levoglucosan from regions around. However, knowledge about the characteristics of levoglucosan distributions on Tibetan glaciers under the different climate systems is poorly understood. In this study, we detected levoglucosan in snow samples from the Zuoqiupu (ZQP) Glacier affected by the Indian summer monsoon and the Muji (MJ) Glacier dominated by the westerlies. Results found that the ZQP Glacier was more heavily affected by fire emissions than the MJ Glacier, caused by stronger emission sources on the windward direction and shorter transport distances. Elevations for the appearance of levoglucosan maxima on glacier surfaces are roughly around the equilibrium line altitudes. However, levoglucosan displays a wider distribution range on the MJ glacier than on the ZQP glacier due to weaker summer melt. Injection height of fire smokes and glacial melt can affect the altitudinal distribution of levoglucosan. Black carbon and levoglucosan show different temporal variations in snow-pit samples on those two glaciers. The post-depositional effects, e.g. the melting and refreezing processes, can modulate the vertical distribution of levoglucosan in snow/ice layers. Our results are helpful for understanding the geochemical behaviors of levoglucosan happened on Tibetan glacier surfaces.Display Omitted
Keywords: Fire emissions; Levoglucosan; Fire tracer; Snow chemistry; Tibetan plateau;
Atmospheric emissions of typical toxic heavy metals from open burning of municipal solid waste in China by Yan Wang; Ke Cheng; Weidong Wu; Hezhong Tian; Peng Yi; Guorui Zhi; Jing Fan; Shuhan Liu (6-15).
Municipal solid waste (MSW) contains considerable hazardous components and the widely-distributed open MSW burning in heavily-populated urban areas can cause direct exposure of hazardous materials to citizens. By determining the best available representation of composition-varying and time-varying emission factors with fuzzy mathematics method and S-shape curves, a comprehensive atmospheric emission inventories of 9 typical toxic heavy metals (THMs, e.g. mercury (Hg), arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), selenium (Se), copper (Cu), zinc (Zn), and nickel (Ni)) from open MSW burning activities in China is established during the period of 2000–2013 for the first time. Further, the emissions in 2013 are allocated at a high spatial resolution of 0.5° × 0.5° grid by surrogate indexes. The results show that 9 typical THMs emissions from open MSW burning are estimated at 21.25 t for Hg, 131.52 t for As, 97.12 t for Pb, 10.12 t for Cd, 50.58 t for Cr, 81.95 t for Se, 382.42 t for Cu, 1790.70 t for Zn, and 43.50 t for Ni, respectively. In terms of spatial variation, the majority of emissions are concentrated in relatively developed and densely-populated regions, especially for the eastern, central and southern regions. Moreover, future emissions are also projected for the period of 2015–2030 based on different scenarios of the independent and collaborative effects of control proposals including minimizing waste, improving MSW incineration ratio, and enhancing waste sorting and recycling, etc. The collaborative effect of the above proposals is expected to bring the most effective reduction to THMs emissions from open MSW burning in China except for Hg. The results will be supplementary to all anthropogenic emissions and useful for relevant policy-making and the improvement of urban air quality as well as human health.Display Omitted
Keywords: MSW; Toxic heavy metals; Open burning; Emission characteristics; Control proposals;
Combined use of land use regression and BenMAP for estimating public health benefits of reducing PM2.5 in Tianjin, China by Li Chen; Mengshuang Shi; Suhuan Li; Zhipeng Bai; Zhongliang Wang (16-23).
To assess the public health benefits of reducing PM2.5 in Tianjin, we created an annual air quality surface with a land use regression (LUR) model conducted at a high spatial resolution (1 km). The predictors included in the final model were population density, road length within a 1000 m buffer, industrial land area within a 2000m buffer and distance to the coast. The fitting R2 and the leave-one-out-cross-validation (LOOCV) R2 of the PM2.5 LUR models were 0.78 and 0.73, respectively, suggesting that the predicted PM2.5 concentrations fitted well with the measured values for the entire year. Daily air quality surfaces were established based on historic concentration data and interpolation method. We evaluated avoided cases of mortality and morbidity in Tianjin, assuming achievement of China's current air quality daily and annual standards (No. GB3095-2012). Reducing the daily average PM2.5 to the daily Class II standard (75 μg/m3), the avoided emergency department visits, the deaths for cardiovascular disease and the deaths for respiratory disease are 85,000 (95% confidence interval (CI), 17,000–150,000), 2000 (95% CI, 920–3100) and 280 (95% CI, 94–460) per year respectively, and the monetary values are 23–42 million yuan, 180–4800 million yuan and 25–670 million yuan per year in 2015 yuan year respectively. Reducing the annual average PM2.5 to the annual Class II standard (35 μg/m3), the avoided emergency department visits, the deaths for cardiovascular disease and the deaths for respiratory disease are 59,000 (95% CI, 12,000–110,000), 1400 (95% CI, 640–2100) and 200 (95% CI, 66–320) per year respectively, and the monetary values are 16–29 million yuan, 130 to 3400 million yuan and 18 to 480 million yuan per year in 2015 yuan year respectively.
Keywords: Land use regression; Public health benefit; BenMAP; PM2.5; Tianjin;
Estimating particulate black carbon concentrations using two offline light absorption methods applied to four types of filter media by Pamela M. Davy; Anja H. Tremper; Eleonora M.G. Nicolosi; Paul Quincey; Gary W. Fuller (24-33).
Atmospheric particulate black carbon has been linked to adverse health outcomes. Additional black carbon measurements would aid a better understanding of population exposure in epidemiological studies as well as the success, or otherwise, of relevant abatement technologies and policies. Two light absorption measurement methods of particles collected on filters have been applied to four different types of filters to provide estimations of particulate black carbon concentrations. The ratio of transmittance (lnI0/I) to reflectance (lnR0/R) varied by filter type and ranged from close to 0.5 (as expected from simple theory) to 1.35 between the four filter types tested. The relationship between light absorption and black carbon, measured by the thermal EC(TOT) method, was nonlinear and differed between filter type and measurement method. This is particularly relevant to epidemiological studies that use light absorption as an exposure metric. An extensive archive of filters was used to derive loading factors and mass extinction coefficients for each filter type. Particulate black carbon time series were then calculated at locations where such measurements were not previously available. When applied to two roads in London, black carbon concentrations were found to have increased between 2011 and 2013, by 0.3 (CI: −0.1, 0.5) and 0.4 (CI: 0.1, 0.9) μg m−3 year−1, in contrast to the expectation from exhaust abatement policies. New opportunities using archived or bespoke filter collections for studies on the health effects of black carbon and the efficacy of abatement strategies are created.Display Omitted
Keywords: Black smoke; Filter absorption; Reflectance; Transmittance;
Uncertainty characterization in the retrieval of an atmospheric point release by Sarvesh Kumar Singh; Pramod Kumar; Grégory Turbelin; Raj Rani (34-50).
The study proposes a methodology in a recent inversion technique, called as Renormalization, to characterize the uncertainties in the reconstruction of a point source. The estimates are derived for measuring the inversion error, the degree of model fit towards measurements (model determination coefficient) and the confidence intervals for the retrieved point source parameters (mainly, location and strength). The inversion error is reflected through an angular estimate which measures the deviation between the measured and predicted concentrations. The uncertainty estimation methodology is evaluated for point source reconstruction studies, using real measurements from two field experiments, known as Fusion Field Trials 2007 (FFT07) in flat terrain and Mock Urban Setting Test (MUST) in urban like terrain. In FFT07 and MUST experiments, the point source location is retrieved with an average Euclidean distance of 22 m and 15 m respectively. The source strength is retrieved, on average, within a factor of 1.5 in both the datasets. The inversion error is observed as 24 o and 21 o in FFT07 and MUST experiment, respectively. The 95% confidence interval estimates show that the uncertainty in the retrieved parameters is relatively large in approximately 50% FFT07 and 30% MUST trials in spite of their closeness towards true source parameters. For a comparative analysis, the interval estimates are also compared with a more general method of uncertainty estimation, Residual Bootstrap Sampling. In most of the trials, we observed that the intervals estimates with the present method are comparable (within 10–20% variations) to bootstrap estimates. The proposed methodology provides near accurate and computationally efficient uncertainty estimates in comparison to the methods based on Hessian and sampling procedures.
Keywords: Confidence bounds; FFT07 field experiment; MUST field experiment; Renormalization; Source reconstruction; Uncertainty;
Seasonal behavior of carbonyls and source characterization of formaldehyde (HCHO) in ambient air by K.H. Lui; Steven Sai Hang Ho; Peter K.K. Louie; C.S. Chan; S.C. Lee; Di Hu; P.W. Chan; Jeffrey Chi Wai Lee; K.F. Ho (51-60).
Gas-phase formaldehyde (HCHO) is an intermediate and a sensitive indicator for volatile organic compounds (VOCs) oxidation, which drives tropospheric ozone production. Effective photochemical pollution control strategies demand a thorough understanding of photochemical oxidation precursors, making differentiation between sources of primary and secondary generated HCHO inevitable. Spatial and seasonal variations of airborne carbonyls based on two years of measurements (2012–2013), coupled with a correlation-based HCHO source apportionment analysis, were determined for three sampling locations in Hong Kong (denoted HT, TC, and YL). Formaldehyde and acetaldehyde were the two most abundant compounds of the total quantified carbonyls. Pearson's correlation analysis (r > 0.7) implies that formaldehyde and acetaldehyde possibly share similar sources. The total carbonyl concentration trends (HT < TC < YL) reflect location characteristics (urban > rural). A regression analysis further quantifies the relative primary HCHO source contributions at HT (∼13%), TC (∼21%), and YL (∼40%), showing more direct vehicular emissions in urban than rural areas. Relative secondary source contributions at YL (∼36%) and TC (∼31%) resemble each other, implying similar urban source contributions. Relative background source contributions at TC could be due to a closed structure microenvironment that favors the trapping of HCHO. Comparable seasonal differences are observed at all stations. The results of this study will aid in the development of a new regional ozone (O3) control policy, as ambient HCHO can enhance O3 production and also be produced from atmospheric VOCs oxidation (secondary HCHO).
Keywords: Carbonyl; Seasonal variation; Source apportionment analysis; Ambient air; Correlation analysis;
Importance of soil NO emissions for the total atmospheric NOx budget of Saxony, Germany by Saúl Molina-Herrera; Edwin Haas; Rüdiger Grote; Ralf Kiese; Steffen Klatt; David Kraus; Tatjana Kampffmeyer; Rainer Friedrich; Henning Andreae; Benjamin Loubet; Christof Ammann; László Horváth; Klaus Larsen; Carsten Gruening; Arnoud Frumau; Klaus Butterbach-Bahl (61-76).
Soils are a significant source for the secondary greenhouse gas NO and assumed to be a significant source of tropospheric NOx in rural areas. Here we tested the LandscapeDNDC model for its capability to simulate magnitudes and dynamics of soil NO emissions for 22 sites differing in land use (arable, grassland and forest) and edaphic as well as climatic conditions. Overall, LandscapeDNDC simulated mean soil NO emissions agreed well with observations (r2 = 0.82). However, simulated day to day variations of NO did only agree weakly with high temporal resolution measurements, though agreement between simulations and measurements significantly increased if data were aggregated to weekly, monthly and seasonal time scales. The model reproduced NO emissions from high and low emitting sites, and responded to fertilization (mineral and organic) events with pulse emissions. After evaluation, we linked the LandscapeDNDC model to a GIS database holding spatially explicit data on climate, land use, soil and management to quantify the contribution of soil biogenic NO emissions to the total NOx budget for the State of Saxony, Germany. Our calculations show that soils of both agricultural and forest systems are significant sources and contribute to about 8% (uncertainty range: 6–13%) to the total annual tropospheric NOx budget for Saxony. However, the contributions of soil NO emission to total tropospheric NOx showed a high spatial variability and in some rural regions such as the Ore Mts., simulated soil NO emissions were by far more important than anthropogenic sources.
Keywords: LandscapeDNDC; Model evaluation; NOx emissions; Soil emissions; Distributed modeling; Emission inventory;
Influences of O2 and O3 on the heterogeneous photochemical reaction of NO2 with humic acids by Chong Han; Wangjin Yang; He Yang; Xiangxin Xue (77-84).
Oxidizing components in the atmosphere may play competitive roles in the heterogeneous photochemical reaction of NO2 with humic acids (HA). Effects of O2 and O3 on the conversion of NO2 to HONO on HA under simulated sunlight were investigated using a flow tube reactor. The uptake coefficient (γ) of NO2 and the HONO formation rate decreased with the increase of the O2 content (0%–20%) and the O3 concentration (0–100 ppb). The HONO yield was observed to be independent of the O2 content, whereas it inversely depended on the O3 concentration. In addition, the aging process of HA by O2 and O3 under irradiation resulted in the decrease in the reactivity of HA toward NO2, as shown by lower γ and HONO formation rate, while it has little influence on the HONO yield. Finally, the mechanism of role of O2 and O3 in the photochemical reaction of NO2 with HA was discussed in detail.
Keywords: Humic acids; NO2; HONO; O2; O3; Competitive roles;
A process-based emission model of volatile organic compounds from silage sources on farms by H.F. Bonifacio; C.A. Rotz; S.D. Hafner; F. Montes; M. Cohen; F.M. Mitloehner (85-97).
Silage on dairy farms can emit large amounts of volatile organic compounds (VOCs), a precursor in the formation of tropospheric ozone. Because of the challenges associated with direct measurements, process-based modeling is another approach for estimating emissions of air pollutants from sources such as those from dairy farms. A process-based model for predicting VOC emissions from silage was developed and incorporated into the Integrated Farm System Model (IFSM, v. 4.3), a whole-farm simulation of crop, dairy, and beef production systems. The performance of the IFSM silage VOC emission model was evaluated using ethanol and methanol emissions measured from conventional silage piles (CSP), silage bags (SB), total mixed rations (TMR), and loose corn silage (LCS) at a commercial dairy farm in central California. With transport coefficients for ethanol refined using experimental data from our previous studies, the model performed well in simulating ethanol emission from CSP, TMR, and LCS; its lower performance for SB could be attributed to possible changes in face conditions of SB after silage removal that are not represented in the current model. For methanol emission, lack of experimental data for refinement likely caused the underprediction for CSP and SB whereas the overprediction observed for TMR can be explained as uncertainty in measurements. Despite these limitations, the model is a valuable tool for comparing silage management options and evaluating their relative effects on the overall performance, economics, and environmental impacts of farm production. As a component of IFSM, the silage VOC emission model was used to simulate a representative dairy farm in central California. The simulation showed most silage VOC emissions were from feed lying in feed lanes and not from the exposed face of silage storages. This suggests that mitigation efforts, particularly in areas prone to ozone non-attainment status, should focus on reducing emissions during feeding. For the simulated dairy farm, a reduction of around 30% was found if cows were housed and fed in a barn rather than in an open lot, and 23% if feeds were delivered as four feedings per day rather than as one. Reducing the exposed face of storage can also be useful. Simulated use of silage bags resulted in 90% and 18% reductions in emissions from the storage face and whole farm, respectively.
Keywords: Volatile organic compounds; Silage; Dairy farm; Emissions; Process-based model; Integrated farm system model;
Effect of temperature-dependent cross sections on O4 slant column density estimation by a space-borne UV–visible hyperspectral sensor by Sang Seo Park; Toshihiko Takemura; Jhoon Kim (98-110).
The sensitivities of oxygen dimer (O4) slant column densities (SCDs) were examined by applying temperature-dependent O4 cross sections using the radiative transfer model (RTM) calculation with the linearized pseudo-spherical vector discrete ordinate radiative transfer model. For the sensitivity study, we used a newly developed cross section database in place of the database used in the operational algorithm. Newly investigated O4 cross section databases for 203 K and 293 K were used for the radiance simulation by interpolating temperature for each atmospheric layer based on the vertical profile of standard atmosphere in the RTM. The effect of the temperature-dependent cross sections was a significant O4 SCD increase of 8.3% with dependence on satellite and solar viewing geometries. Furthermore, the O4 SCD generally increased by an estimated 3.9% based on the observation geometries of the Ozone Monitoring Instrument. For the long-term comparison, the O4 SCD estimated from the temperature-dependent cross sections corrects 20% of the total underestimation of O4 SCD between the observation and simulation. Although the surface pressure variation and background aerosol effect also correct the O4 SCD discrepancy, the effect of temperature-dependent cross sections was more important than the effects of surface pressure variation and background aerosols. Therefore, temperature dependence of the cross section in the RTM calculation is essential for the accurate simulation of O4 SCD.
Keywords: O4; Slant column density; Differential optical absorption spectroscopy; Cross section;
Inhalation exposure and health risk levels to BTEX and carbonyl compounds of traffic policeman working in the inner city of Bangkok, Thailand by Navaporn Kanjanasiranont; Tassanee Prueksasit; Daisy Morknoy (111-120).
Benzene, toluene, ethylbenzene and xylenes (BTEX) and carbonyl compounds (CCs) are recognized traffic-related air pollutants in urban environments and are the focus of this study. In Bangkok, the BTEX and CC concentrations in both ambient air and personal exposure samples were studied during two periods (April–May and August–September 2014) at four different sampling sites around the Pathumwan District (three intersections and one T-junction). Traffic policemen, representing the high-exposure group for these toxic air pollutants, were observed, and the health risk to these workers was evaluated. Toluene was the predominant aromatic compound in the ambient and personal exposure samples. The maximum average ambient concentration of BTEX was 2968.96 μg/m3. Formaldehyde and acetaldehyde were the most abundant CCs at all of the sampling sites, with the greatest mean concentrations of these substances being 21.50 μg/m3 and 64.82 μg/m3, respectively. In the personal exposure samples, the highest levels of BTEX, formaldehyde and acetaldehyde concentrations were 2231.85 μg/m3, 10.61 μg/m3, and 16.03 μg/m3, respectively. In terms of risk assessment, benzene posed the greatest cancer risk (at the 95% CI), followed by toluene, acetaldehyde and formaldehyde (1.15E-02, 5.14E-03, 2.84E-04, and 2.52E-04, respectively). Three risk factors were investigated to reduce the total cancer risk levels: reducing the chemical concentration, exposure time and exposure duration. The use of a mask (chemical concentration) was the best way to reduce the risk to traffic police. However, the risk value of benzene (average 1.57E-05) was still higher than an acceptable value when using a mask.
Keywords: BTEX; Carbonyl compounds; Health risk assessment; Traffic policemen; Bangkok;
Haagen-Smit Prize 2016 by Hanwant Singh (121-122).
Responses of human health and vegetation exposure metrics to changes in ozone concentration distributions in the European Union, United States, and China by Allen S. Lefohn; Christopher S. Malley; Heather Simon; Benjamin Wells; Xiaobin Xu; Li Zhang; Tao Wang (123-145).
The impacts of surface ozone (O3) on human health and vegetation have prompted O3 precursor emission reductions in the European Union (EU) and United States (US). In contrast, until recently, emissions have increased in East Asia and most strongly in China. As emissions change, the distribution of hourly O3 concentrations also changes, as do the values of exposure metrics. The distribution changes can result in the exposure metric trend patterns changing in a similar direction as trends in emissions (e.g., metrics increase as emissions increase) or, in some cases, in opposite directions. This study, using data from 481 sites (276 in the EU, 196 in the US, and 9 in China), investigates the response of 14 human health and vegetation O3 exposure metrics to changes in hourly O3 concentration distributions over time. At a majority of EU and US sites, there was a reduction in the frequency of both relatively high and low hourly average O3 concentrations. In contrast, for some sites in mainland China and Hong Kong, the middle of the distribution shifted upwards but the low end did not change and for other sites, the entire distribution shifted upwards. The responses of the 14 metrics to these changes at the EU, US, and Chinese sites were varied, and dependent on (1) the extent to which the metric was determined by relatively high, moderate, and low concentrations and (2) the relative magnitude of the shifts occurring within the O3 concentration distribution. For example, the majority of the EU and US sites experienced decreasing trends in the magnitude of those metrics associated with higher concentrations. For the sites in China, all of the metrics either increased or had no trends. In contrast, there were a greater number of sites that had no trend for those metrics determined by a combination of moderate and high O3 concentrations. A result of our analyses is that trends in mean or median concentrations did not appear to be well associated with some exposure metrics applicable for assessing human health or vegetation effects. The identification of shifting patterns in the O3 distribution and the resulting changes in O3 exposure metrics across regions with large emission increases and decreases is an important step in examining the linkage between emissions and exposure metric trends. The results provide insight into the utility of using specific exposure metrics for assessing emission control strategies.Display Omitted
Keywords: Binning concentrations; Exposure metrics; Ozone distributions; NOx scavenging; Shifting concentrations; Trends;
Effect of Prudhoe Bay emissions on atmospheric aerosol growth events observed in Utqiaġvik (Barrow), Alaska by Katheryn R. Kolesar; Jillian Cellini; Peter K. Peterson; Anne Jefferson; Thomas Tuch; Wolfram Birmili; Alfred Wiedensohler; Kerri A. Pratt (146-155).
The Arctic is a rapidly changing ecosystem, with complex aerosol-cloud-climate feedbacks contributing to more rapid warming of the region as compared to the mid-latitudes. Understanding changes to particle number concentration and size distributions is important to constraining estimates of the effect of anthropogenic activity on the region. During six years of semi-continuous measurements of particle number size distributions conducted near Utqiaġvik (Barrow), Alaska, 37 particle-growth events were observed. The majority of events occurred during spring and summer with a monthly maximum in June, similar to other Arctic sites. Based on backward air mass trajectory analysis, similar numbers of particle-growth events were influenced by marine (46%) and Prudhoe Bay air masses (33%), despite air primarily coming from the Arctic Ocean (75 ± 2% of days) compared to Prudhoe Bay (8 ± 2% of days). The corresponding normalized particle-growth event frequency suggests that emissions from Prudhoe Bay could induce an average of 92 particle-growth events, more than all other air mass sources combined, at Barrow annually. Prudhoe Bay is currently the third largest oil and gas field in the United States, and development in the Arctic region is expected to expand throughout the 21st century as the extent of summertime sea ice decreases. Elevated particle number concentrations due to human activity are likely to have profound impacts on climate change in the Arctic through direct, indirect, and surface albedo feedbacks, particularly through the addition of cloud condensation nuclei.Display Omitted
Keywords: Particle growth; Arctic aerosols; Oil and gas emissions; Prudhoe Bay;
Correlation of gravestone decay and air quality 1960–2010 by H.D. Mooers; M.J. Carlson; R.M. Harrison; R.J. Inkpen; S. Loeffler (156-171).
Evaluation of spatial and temporal variability in surface recession of lead-lettered Carrara marble gravestones provides a quantitative measure of acid flux to the stone surfaces and is closely related to local land use and air quality. Correlation of stone decay, land use, and air quality for the period after 1960 when reliable estimates of atmospheric pollution are available is evaluated. Gravestone decay and SO2 measurements are interpolated spatially using deterministic and geostatistical techniques. A general lack of spatial correlation was identified and therefore a land-use-based technique for correlation of stone decay and air quality is employed. Decadally averaged stone decay is highly correlated with land use averaged spatially over an optimum radius of ≈7 km even though air quality, determined by records from the UK monitoring network, is not highly correlated with gravestone decay. The relationships among stone decay, air-quality, and land use is complicated by the relatively low spatial density of both gravestone decay and air quality data and the fact that air quality data is available only as annual averages and therefore seasonal dependence cannot be evaluated. However, acid deposition calculated from gravestone decay suggests that the deposition efficiency of SO2 has increased appreciably since 1980 indicating an increase in the SO2 oxidation process possibly related to reactions with ammonia.
Keywords: Gravestone decay; Acid deposition; Air quality; Land use; West midlands; United Kingdom; SO2 deposition velocity;
Heterogeneous kinetics, products, and mechanisms of ferulic acid particles in the reaction with NO3 radicals by Changgeng Liu; Peng Zhang; Xiaoying Wen; Bin Wu (172-179).
Methoxyphenols, as an important component of wood burning, are produced by lignin pyrolysis and considered to be the potential tracers for wood smoke emissions. In this work, the heterogeneous reaction between ferulic acid particles and NO3 radicals was investigated. Six products including oxalic acid, 4-vinylguaiacol, vanillin, 5-nitrovanillin, 5-nitroferulic acid, and caffeic acid were confirmed by gas chromatography-mass spectrometry (GC-MS). In addition, the reaction mechanisms were proposed and the main pathways were NO3 electrophilic addition to olefin and the meta-position to the hydroxyl group. The uptake coefficient of NO3 radicals on ferulic acid particles was 0.17 ± 0.02 and the effective rate constant under experimental conditions was (1.71 ± 0.08) × 10−12 cm3 molecule−1 s−1. The results indicate that ferulic acid degradation by NO3 can be an important sink at night.Display Omitted
Keywords: Methoxyphenols; NO3 radicals; Heterogeneous reaction; Aerosol mass spectrometry;
Comprehensive chemical characterization of industrial PM2.5 from steel industry activities by Alexandre Sylvestre; Aurélie Mizzi; Sébastien Mathiot; Fanny Masson; Jean L. Jaffrezo; Julien Dron; Boualem Mesbah; Henri Wortham; Nicolas Marchand (180-190).
Industrial sources are among the least documented PM (Particulate Matter) source in terms of chemical composition, which limits our understanding of their effective impact on ambient PM concentrations. We report 4 chemical emission profiles of PM2.5 for multiple activities located in a vast metallurgical complex. Emissions profiles were calculated as the difference of species concentrations between an upwind and a downwind site normalized by the absolute PM2.5 enrichment between both sites. We characterized the PM2.5 emissions profiles of the industrial activities related to the cast iron (complex 1) and the iron ore conversion processes (complex 2), as well as 2 storage areas: a blast furnace slag area (complex 3) and an ore terminal (complex 4). PM2.5 major fractions (Organic Carbon (OC) and Elemental Carbon (EC), major ions), organic markers as well as metals/trace elements are reported for the 4 industrial complexes. Among the trace elements, iron is the most emitted for the complex 1 (146.0 mg g−1 of PM2.5), the complex 2 (70.07 mg g−1) and the complex 3 (124.4 mg g−1) followed by Al, Mn and Zn. A strong emission of Polycyclic Aromatic Hydrocarbons (PAH), representing 1.3% of the Organic Matter (OM), is observed for the iron ore transformation complex (complex 2) which merges the activities of coke and iron sinter production and the blast furnace processes. In addition to unsubstituted PAHs, sulfur containing PAHs (SPAHs) are also significantly emitted (between 0.011 and 0.068 mg g−1) by the complex 2 and could become very useful organic markers of steel industry activities. For the complexes 1 and 2 (cast iron and iron ore converters), a strong fraction of sulfate ranging from 0.284 to 0.336 g g−1) and only partially neutralized by ammonium, is observed indicating that sulfates, if not directly emitted by the industrial activity, are formed very quickly in the plume. Emission from complex 4 (Ore terminal) are characterized by high contribution of Al (125.7 mg g−1 of PM2.5) but also, in a lesser extent, of Fe, Mn, Ti and Zn. We also highlighted high contribution of calcium ranging from 0.123 to 0.558 g g−1 for all of the industrial complexes under study. Since calcium is also widely used as a proxy of the dust contributions in source apportionment studies, our results suggest that this assumption should be reexamined in environments impacted by industrial emissions.Schematic representation of the method used to determinate the industrial profiles using downwind and upwind sites: A) Side view, B) overhead view.Display Omitted
Keywords: Chemical profiles; PM2.5; Steel industry; Organics markers; Trace elements;
Dry deposition and canopy uptake in Mediterranean holm-oak forests estimated with a canopy budget model: A focus on N estimations by L. Aguillaume; S. Izquieta-Rojano; H. García-Gómez; D. Elustondo; J.M. Santamaría; R. Alonso; A. Avila (191-200).
Bulk/wet and throughfall fluxes of major compounds were measured from June 2011 to June 2013 at four Mediterranean holm-oak (Quercus ilex) forests in the Iberian Peninsula. Regression analysis between net throughfall fluxes and precipitation indicated that the best defined canopy process was leaching for K+ and uptake for NH4 + at all sites. A more variable response between sites was found for Na+, Ca2+, SO4 2- and Cl−, which suggests that the interplay of dry deposition, leaching and uptake at the canopy was different depending on site climate and air quality characteristics.A canopy budget model (CBM) was used to try to discriminate between the canopy processes and enable to estimate dry deposition and uptake fluxes at three of the sites that complied with the model specifications. To derive N uptake, an efficiency factor of NH4 + vs. NO3 − uptake (xNH4) corresponding to moles of NH4 + taken up for each NO3 − mol, has to be determined. Up to now, a value of 6 has been proposed for temperate forests, but we lack information for Mediterranean forests. Experimental determination of N absorption on Quercus ilex seedlings in Spain suggests efficiency factors from 1 to 6. Based on these values, a sensitivity analysis for xNH4 was performed and the NH4 ―N and NO3 ―N modeled dry deposition was compared with dry deposition estimated with independent methods (inferential modeling and washing of branches). At two sites in NE Spain under a milder Mediterranean climate, the best match was obtained for xNH4 = 6, corroborating results from European temperate forests. Based on this value, total DIN deposition was 12–13 kg N ha−1 y−1 at these sites. However, for a site in central Spain under drier conditions, variation of the NH4 + efficiency factor had little effect on DD estimates (which ranged from 2 to 2.6 kg N ha−1 y−1 with varying xNH4); when added to wet deposition, this produced a total N deposition in the range 2.6–3.4 kg N ha−1 y−1. Dry deposition was the predominant pathway for N, accounting for 60–80% of total deposition, while for base cations wet deposition dominated (55–65%). Nitrogen deposition values at the northwestern sites were close to the empirical critical load proposed for evergreen sclerophyllous Mediterranean forests (15–17 kg N ha−1 y−1). When organic N deposition at these forests is added (3 kg N ha−1 y−1), the total N input to the sites in NE Spain are close to the critical loads for Mediterranean evergreen oak forests.
Keywords: Wet deposition; Throughfall; Canopy exchange; Mediterranean; Nitrogen; Critical loads;
Ambient air quality measurements from a continuously moving mobile platform: Estimation of area-wide, fuel-based, mobile source emission factors using absolute principal component scores by Timothy Larson; Timothy Gould; Erin A. Riley; Elena Austin; Jonathan Fintzi; Lianne Sheppard; Michael Yost; Christopher Simpson (201-211).
We have applied the absolute principal component scores (APCS) receptor model to on-road, background-adjusted measurements of NOx, CO, CO2, black carbon (BC), and particle number (PN) obtained from a continuously moving platform deployed over nine afternoon sampling periods in Seattle, WA. Two Varimax-rotated principal component features described 75% of the overall variance of the observations. A heavy-duty vehicle feature was correlated with black carbon and particle number, whereas a light-duty feature was correlated with CO and CO2. NOx had moderate correlation with both features. The bootstrapped APCS model predictions were used to estimate area-wide, average fuel-based emission factors and their respective 95% confidence limits. The average emission factors for NOx, CO, BC and PN (14.8, 18.9, 0.40 g/kg, and 4.3 × 1015 particles/kg for heavy duty vehicles, and 3.2, 22.4, 0.016 g/kg, and 0.19 × 1015 particles/kg for light-duty vehicles, respectively) are consistent with previous estimates based on remote sensing, vehicle chase studies, and recent dynamometer tests. Information on the spatial distribution of the concentrations contributed by these two vehicle categories relative to background during the sampling period was also obtained.
Keywords: Vehicle exhaust emission factors; Mobile monitoring; Principal component analysis; Traffic related air pollution; On-road air pollution;
New insights into the parametrization of temperature and light responses of mono - and sesquiterpene emissions from Aleppo pine and rosemary by M. Staudt; I. Bourgeois; R. Al Halabi; W. Song; J. Williams (212-221).
Phytogenic emission of large volatile organic compounds (VOCs) such as monoterpenes (MTs) and sesquiterpenes (SQTs) are key precursors to the formation and growth of atmospheric particles. However, controlled environment studies to elucidate emission responses to temperature and light are still sparse. In this study, the volatile contents and emission responses of Aleppo pine and Rosemary have been investigated. These two common Mediterranean species store semivolatiles inside (resin ducts) and outside (trichomes) their foliage tissues respectively. Both species emitted mainly MTs with basal emission rates of around 5 (Rosemary) and 10 (pine) μg g−1 h−1 and SQTs about one order of magnitude lower. In Aleppo pine, two volatile sources could be clearly distinguished: 1) de-novo synthesized emission of (E)-β-ocimene and linalool, which accounted for about 70% of the total VOC release, were not found in foliar VOC extracts and expressed light dependency (LD) and temperature responses typical for enzyme driven emissions; and 2) storage-derived emissions of various MTs and SQTs whose emissions increased exponentially with temperature, showed no light dependency and were all present in leaf extracts. In Rosemary, all emitted MTs and SQTs including many oxygenated compounds, showed responses typical for stored volatiles and were all found in leaf extracts. The emissions of individual volatiles or volatile classes could be well described with the commonly applied empirical algorithms developed for LD or non LD emissions. However, the shapes of the temperature responses, and hence the deduced coefficient values, were significantly different between oxygenated and non-oxygenated compounds. They also differed between the storage-derived emissions of the two plant species, for individual VOCs or VOC classes. We address the possible reasons for this variation in temperature responses and argue that they are mostly due to molecular interactions along the species specific leaf-internal diffusion paths including the build-up of transient VOC pools and degradation.Display Omitted
Keywords: Biogenic emissions; Oxygenated compounds; Isoprene; Temperature dependency; Light response curve;
Impact of future climate policy scenarios on air quality and aerosol-cloud interactions using an advanced version of CESM/CAM5: Part I. model evaluation for the current decadal simulations by Timothy Glotfelty; Jian He; Yang Zhang (222-239).
A version of the Community Earth System Model modified at the North Carolina State University (CESM-NCSU) is used to simulate the current and future atmosphere following the representative concentration partway scenarios for stabilization of radiative forcing at 4.5 W m−2 (RCP4.5) and radiative forcing of 8.5 W m−2 (RCP8.5). Part I describes the results from a comprehensive evaluation of current decadal simulations. Radiation and most meteorological variables are well simulated in CESM-NCSU. Cloud parameters are not as well simulated due in part to the tuning of model radiation and general biases in cloud variables common to all global chemistry-climate models. The concentrations of most inorganic aerosol species (i.e., SO4 2-, NH4 +, and NO3 −) are well simulated with normalized mean biases (NMBs) typically less than 20%. However, some notable exceptions are European NH4 +, which is overpredicted by 33.0–42.2% due to high NH3 emissions and irreversible coarse mode condensation, and Cl−, that is negatively impacted by errors in emissions driven by wind speed and overpredicted HNO3. Carbonaceous aerosols are largely underpredicted following the RCP scenarios due to low emissions of black carbon, organic carbon, and anthropogenic volatile compounds in the RCP inventory and efficient wet removal. This results in underpredictions of PM2.5 and PM10 by 6.4–55.7%. The column mass abundances are reasonably well simulated. Larger biases occur in surface mixing ratios of trace gases in CESM-NCSU, likely due to numerical diffusion from the coarse grid spacing of the CESM-NCSU simulations or errors in the magnitudes and vertical structure of emissions. This is especially true for SO2 and NO2. The mixing ratio of O3 is overpredicted by 38.9–76.0% due to the limitations in the O3 deposition scheme used in CESM and insufficient titration resulted from large underpredictions in NO2. Despite these limitations, CESM-NCSU reproduces reasonably well the current atmosphere in terms of radiation, clouds, meteorology, trace gases, aerosols, and aerosol-cloud interactions, making it suitable for future climate simulations.
Keywords: CESM/CAM5; Representative concentration pathways; Earth system modeling; Current air quality; Model evaluation; Aerosol indirect effects;
Effect of ambient temperature on species lumping for total organic gases in gasoline exhaust emissions by Anirban Roy; Yunsoo Choi (240-245).
Volatile organic compound (VOCs) emissions from sources often need to be compressed or “lumped” into species classes for use in emissions inventories intended for air quality modeling. This needs to be done to ensure computational efficiency. The lumped profiles are usually reported for one value of ambient temperature. However, temperature-specific detailed profiles have been constructed in the recent past - the current study investigates how the lumping of species from those profiles into different atmospheric chemistry mechanisms is affected by temperature, considering three temperatures (−18 °C, −7 °C and 24 °C). The mechanisms considered differed on the assumptions used for lumping: CB05 (carbon bond type), SAPRC (ozone formation potential) and RACM2 (molecular surrogate and reactivity weighting). In this space, four sub-mechanisms for SAPRC were considered. Scaling factors were developed for each lumped model species and mechanism in terms of moles of lumped species per unit mass. Species which showed a direct one-to-one mapping (SAPRC/RACM2) reported scaling factors that were unchanged across mechanisms. However, CB05 showed different trends since one compound often is mapped onto multiple model species, out of which the paraffinic double bond (PAR) is predominant. Temperature-dependent parameterizations for emission factors pertaining to each lumped species class and mechanism were developed as part of the study. Here, the same kind of model species showed varying lumping parameters across the different mechanisms. These differences could be attributed to differing approaches in lumping. The scaling factors and temperature-dependent parameterizations could be used to update emissions inventories such as MOVES or SMOKE for use in chemical transport modeling.
Keywords: Speciation; Lumping; Temperature;
Emissions of ammonia, carbon dioxide and particulate matter from cage-free layer houses in California by Xingjun Lin; Ruihong Zhang; Shumei Jiang; Hamed El-Mashad; Hongwei Xin (246-255).
Cage-free housing systems have attracted considerable attention in the United States recently as they provide more space and other resources (such as litter area, perches, and nest boxes) for hens and are considered to be more favorable from the standpoint of hen welfare. This study was carried out to quantify emissions of aerial ammonia (NH3), carbon dioxide (CO2) and particulate matter (PM10 and PM2.5) from cage-free layer houses in California and compare the values with those for other types of layer houses. Two commercial cage-free houses with 38,000 hens each were monitored from March 1, 2012 to April 1, 2013. Results show that NH3 and CO2 concentrations in the houses were affected by ventilation rate, which was largely influenced by ambient air temperature. The PM10 and PM2.5 concentrations in the houses depended on the activity of birds, ventilation rate and relative humidity of the ambient air. The average emission rates of NH3, CO2, PM10 and PM2.5 were 0.29, 89.9, 0.163 and 0.020 g d−1 hen−1, respectively. The NH3 emission rate determined in this study was higher than those of aviary houses. The PM10 and PM2.5 emission rates were higher than those reported for high-rise layer houses.
Keywords: Ventilation rate; Laying-hen; Egg production; Bird activity; Continuous monitoring;
The impact of atmospheric dust deposition and trace elements levels on the villages surrounding the former mining areas in a semi-arid environment (SE Spain) by David Sánchez Bisquert; José Matías Peñas Castejón; Gregorio García Fernández (256-269).
It is understood that particulate matter in the atmosphere from metallic mining waste has adverse health effects on populations living nearby. Atmospheric deposition is a process connecting the mining wasteswith nearby ecosystems. Unfortunately, very limited information is available about atmospheric deposition surrounding rural metallic mining areas. This article will focus on the deposition from mining areas, combined with its impact on nearby rural built areas and populations. Particle samples were collected between June 2011 and March 2013. They were collected according to Spanish legislation in ten specialised dust collectors. They were located near populations close to a former Mediterranean mining area, plus a control, to assess the impact of mining waste on these villages. This article and its results have been made through an analysis of atmospheric deposition of these trace elements (Mn, Zn, As, Cd and Pb). It also includes an analysis of total dust flux. Within this analysis it has considered the spatial variations of atmospheric deposition flux in these locations. The average annual level of total bulk deposition registered was 42.0 g m-2 per year. This was higher than most of the areas affected by a Mediterranean climate or in semi-arid conditions around the world. Regarding the overall analysis of trace elements, the annual bulk deposition fluxes of total Zn far exceeded the values of other areas. While Mn, Cd and Pb showed similar or lower values, and in part much lower than those described in other Mediterranean mining areas. This study confirmed some spatial variability of dust and trace elements, contained within the atmospheric deposition. From both an environmental and a public health perspective, environmental managers must take into account the cumulative effect of the deposition of trace elements on the soil and air quality around and within the villages surrounding metallic mining areas.Display Omitted
Sulfur, arsenic, fluorine and mercury emissions resulting from coal-washing byproducts: A critical component of China's emission inventory by Chao Zhao; Kunli Luo (270-278).
The coal-washing rate in China increased from 1991 to 2014 and shows a particular increase from ∼22% to ∼60% since 2002. However, few studies pay attention to the use and disposal of the coal-washing byproducts (CWBs). A preliminary estimate of the likely S, As, F and Hg contents and emissions from the combustion of CWBs in China was determined in this work. About 632 million tons of CWBs, including middling coal, flotation tailing coal and coal slime, were produced in China in 2014. About 4.03%, 20.80%, 1.48%, and 73.25% CWBs were used for thermal power, industry, domestic and discard. The mean S, As, F and Hg contents of CWBs are 1.52%, 14.04 mg/kg, 216.31 mg/kg and 0.27 mg/kg, respectively. SO2 emissions in 2014 from the combustion of CWBs were ∼5.76 million tons, similar to that released into the atmosphere by China's coal-fired power plants, accounting for ∼29% of the country's total SO2 emissions. Arsenic, F and Hg emissions from CWBs were 1 599.54, 61 575.07 and 77.16 tons, respectively. These emissions have become a critical component of air pollution in China.Display Omitted
Keywords: China; Coal-washing byproducts; Harmful elements emission;
Relative impact of on-road vehicular and point-source industrial emissions of air pollutants in a medium-sized Andean city by C.M. González; C.D. Gómez; N.Y. Rojas; H. Acevedo; B.H. Aristizábal (279-289).
Cities in emerging countries are facing a fast growth and urbanization; however, the study of air pollutant emissions and its dynamics is scarce, making their populations vulnerable to potential effects of air pollution. This situation is critical in medium-sized urban areas built along the tropical Andean mountains. This work assesses the contribution of on-road vehicular and point-source industrial activities in the medium-sized Andean city of Manizales, Colombia. Annual fluxes of criteria pollutants, NMVOC, and greenhouse gases were estimated. Emissions were dominated by vehicular activity, with more than 90% of total estimated releases for the majority of air pollutants. On-road vehicular emissions for CO (43.4 Gg/yr) and NMVOC (9.6 Gg/yr) were mainly associated with the use of motorcycles (50% and 81% of total CO and NMVOC emissions respectively). Public transit buses were the main source of PM10 (47%) and NOx (48%). The per-capita emission index was significantly higher in Manizales than in other medium-sized cities, especially for NMVOC, CO, NOx and CO2. The unique mountainous terrain of Andean cities suggest that a methodology based on VSP model could give more realistic emission estimates, with additional model components that include slope and acceleration. Food and beverage facilities were the main contributors of point-source industrial emissions for PM10 (63%), SOx (55%) and NOx (45%), whereas scrap metal recycling had high emissions of CO (73%) and NMVOC (47%). Results provide the baseline for ongoing research in atmospheric modeling and urban air quality, in order to improve the understanding of air pollutant fluxes, transport and transformation in the atmosphere. In addition, this emission inventory could be used as a tool to identify areas of public health exposure and provide information for future decision makers.
Keywords: Air pollution; Emission inventories; On-road vehicular sources; Industrial point-sources; Medium-sized cities;
Interaction of ozone and carbon dioxide with polycrystalline potassium bromide and its atmospheric implication by Alexander V. Levanov; Oksana Ya. Isaikina; Ivan B. Maksimov; Valerii V. Lunin (290-297).
It has been discovered for the first time that gaseous ozone in the presence of carbon dioxide and water vapor interacts with crystalline potassium bromide giving gaseous Br2 and solid salts KHCO3 and KBrO3. Molecular bromine and hydrocarbonate ion are the products of one and the same reaction described by the stoichiometric equation 2KBr(cr.) + O3(gas) + 2CO2(gas) + H2O(gas) → 2KHCO3(cr.) + Br2(gas) + O2(gas). The dependencies of Br2, KHCO3 and KBrO3 formation rates on the concentrations of O3 and CO2, humidity of initial gas mixture, and temperature have been investigated. A kinetic scheme has been proposed that explains the experimental regularities found in this work on the quantitative level. According to the scheme, the formation of molecular bromine and hydrocarbonate is due to the reaction between hypobromite BrO−, the primary product of bromide oxidation by ozone, with carbon dioxide and water; bromate results from consecutive oxidation of bromide ion by ozone Br − → + O 3 , − O 2 BrO − → + O 3 , − O 2 BrO 2 − → + O 3 , − O 2 BrO 3 − .Display Omitted
Keywords: Ozone; Bromide; Molecular bromine; Carbon dioxide; Kinetics; Heterogeneous chemical reactions;
Climatological analysis of aerosol optical properties over East Africa observed from space-borne sensors during 2001–2015 by Richard Boiyo; K. Raghavendra Kumar; Tianliang Zhao; Yansong Bao (298-313).
The present study is aimed at analyzing spatial and temporal characteristics of aerosols retrieved from MODerate resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI) sensors over East Africa (EA). Data spanning for a period of 15 years during 2001–2015 was used to investigate aerosol optical depth (AOD550), Ångstrom exponent (AE470-660) and absorption aerosol Index (AAI) over EA and selected locations within EA. Validation results of MODIS-Terra versus the Aerosol Robotic NETwork (AERONET) AOD550 revealed that the former underestimated aerosol loading over the studied regions due to uncertainties in surface reflectance. The annual mean AOD550, AAI, and AE470-660 were found to be 0.20 ± 0.01, 0.81 ± 0.03, and 1.39 ± 0.01, respectively with peak values observed during the local dry seasons. The spatial seasonal distributions of mean AOD550 suggested high (low) values during the local dry (wet) periods. The high AOD values found along the borders of southwest of Uganda were attributed to smoke particles; while higher (lower) values of AE470-660 (AAI) dominated most parts of the study domain. Low AOD (0.1–0.2) centers were located in high-altitude regions with relatively high vegetation cover over western and central parts of Kenya, and central and northern parts of Tanzania. Furthermore, latitudinal and longitudinal gradients in AOD550 showed a “southern low and northern high” and a “western low and eastern high” profile, respectively during JJA, as other seasons showed heterogeneous variations. Trend analysis revealed a general increase in AOD and AAI and a decrease in AE; while impact factors significantly affected AOD distribution over EA. HYSPLIT back trajectory analyses revealed diverse transport pathways originated from the Arabian Deserts, central Africa, and southwest of Indian Ocean along with locally produced aerosols during different seasons.Display Omitted
Keywords: MODIS; OMI; AOD; NDVI; East Africa;
Multiphase reactivity of gaseous hydroperoxide oligomers produced from isoprene ozonolysis in the presence of acidified aerosols by Matthieu Riva; Sri Hapsari Budisulistiorini; Zhenfa Zhang; Avram Gold; Joel A. Thornton; Barbara J. Turpin; Jason D. Surratt (314-322).
Ozonolysis of alkenes results in the formation of primary ozonides (POZs), which can subsequently decompose into carbonyl compounds and stabilized Criegee intermediates (sCIs). The sCIs generated from isoprene ozonolysis include the simplest congener, formaldehyde oxide (CH2OO), and isomers of C4-sCI. Although the bimolecular reaction with H2O is expected to be the main fate of sCIs, it was reported that sCIs can also react with carboxylic acids and/or organic hydroperoxides leading to gas-phase oligomeric compounds. While the impact of the gas-phase composition (H2O, sCI scavenger) on the formation of such products was recently studied, their fate remains unclear. In the present work, formation of oligomeric hydroperoxides from isoprene ozonolysis, proposed as reaction products composed of the sCI as a chain unit and formed from the insertion of sCI into a hydroperoxide or a carboxylic acid, was systematically examined in the presence of aerosol with varying compositions. The effect of hydroxyl (OH) radicals on the gas- and particle-phase compositions was investigated using diethyl ether as an OH radical scavenger. Thirty-four oligomeric compounds resulting from the insertion of sCIs into organic hydroperoxides or carboxylic acids were identified using iodide chemical ionization high-resolution mass spectrometry. Large reactive uptake onto acidified sulfate aerosol was observed for most of the characterized gaseous oligomeric species, whereas the presence of organic coatings and the lack of aerosol water significantly reduced or halted the reactive uptake of these species. These results indicate that highly oxidized molecules, such as hydroperoxides, could undergo multiphase reactions, which are significantly influenced by the chemical composition of seed aerosol. Furthermore, in addition to functionalization and accretion, decomposition and re-volatilization should be considered in SOA formation.
Keywords: HOMs; Heterogeneous reaction; Criegee; HR-ToF-CIMS; SOA;
Responses of CO2 emission and pore water DOC concentration to soil warming and water table drawdown in Zoige Peatlands by Gang Yang; Mei Wang; Huai Chen; Liangfeng Liu; Ning Wu; Dan Zhu; Jianqing Tian; Changhui Peng; Qiuan Zhu; Yixin He (323-329).
Peatlands in Zoige Plateau contains more than half of peatland carbon stock in China. This part of carbon is losing with climate change through dissolved organic carbon (DOC) export and carbon dioxide (CO2) emissions, both of which are vulnerable to the environmental changes, especially on the Zoige Plateau with a pace of twice the observed rate of global climate warming. This research aimed to understand how climate change including soil warming, rainfall reduction and water table change affect CO2 emissions and whether the trends of changes in CO2 emission are consistent with those of pore water DOC concentration. A mesocosm experiment was designed to investigate the CO2 emission and pore water DOC during the growing seasons of 2009–2010 under scenarios of passive soil warming, 20% rainfall reduction and changes to the water table levels. The results showed a positive relationship between CO2 emission and DOC concentration. For single factor effect, we found no significant relationship between water table and CO2 emission or DOC concentration. However, temperature at 5 cm depth was found to have positive linear relationship with CO2 emission and DOC concentration. The combined effect of soil warming and rainfall reduction increased CO2 emission by 96.8%. It suggested that the drying and warming could stimulate potential emission of CO2. Extending this result to the entire peatland area in Zoige Plateau translates into 0.45 Tg CO2 emission per year over a growing season. These results suggested that the dryer and warmer Zoige Plateau will increase CO2 emission. We also found the contribution rate of DOC concentration to CO2 emission was increased by 12.1% in the surface layer and decreased by 13.8% in the subsurface layer with combined treatment of soil warming and rainfall reduction, which indicated that the warmer and dryer environmental conditions stimulate surface peat decomposition process.Display Omitted
Keywords: Qinghai-Tibetan Plateau; Peatlands; Mesocosm experiment; Climate change; DOC;
Submicron particle dynamics for different surfaces under quiescent and turbulent conditions by Karn Vohra; Kunal Ghosh; S.N. Tripathi; I. Thangamani; P. Goyal; Anu Dutta; V. Verma (330-344).
Experiments were conducted using CsI aerosols in a small scale test chamber to simulate behaviour of aerosols in the containment of a nuclear reactor. The primary focus of the study was on submicron particles (14.3 nm–697.8 nm) due to their hazardous effect on human health. Different wall surfaces, viz., plexiglass, concrete and sandpaper were chosen to study the effect of surface roughness on dry deposition velocity under both quiescent and turbulent conditions. An analytical approach to calculate dry deposition velocity of submicron particles for rough surfaces has been proposed with an improvement in the existing parameterization for shift in the velocity boundary layer. The predicted deposition velocity with the improved parameterization was found to have better agreement with published measured data of Lai and Nazaroff (2005) compared to the existing parameterizations (Wood, 1981; Zhao and Wu, 2006b). There was a significant reduction in root mean square error (RMSE) between predicted, using the improved parameterization and measured deposition velocity (upto 100%) compared to earlier ones. The new analytical deposition approach was coupled with volume conserving semi-implicit coagulation model. This aerosol dynamic model was evaluated against explicit particle size distribution for the first time for rough surfaces. Normalized RMSE between simulated and measured particle size distribution varied in the range of 2%–20% at different instances. The model seems to closely predict submicron particle behaviour in indoor environment.
Keywords: Coagulation; Deposition; Submicron; Turbulence;
Titanium dioxide (TiO2) fine particle capture and BVOC emissions of Betula pendula and Betula pubescens at different wind speeds by Janne V. Räsänen; Jari T.T. Leskinen; Toini Holopainen; Jorma Joutsensaari; Pertti Pasanen; Minna Kivimäenpää (345-353).
Trees are known to affect air quality by capturing a remarkable amount of particles from the atmosphere. However, the significance of trees in removing very fine particles (diameter less than 0.5 μm) is not well understood. We determined particle capture efficiency (Cp) of two birch species: Betula pendula and Betula pubescens by using inert titanium dioxide fine particles (TiO2, geometric mean diameter 0.270 μm) at three wind speeds (1, 3 and 6 ms−1) in a wind tunnel. Capture efficiencies were determined by measuring densities of TiO2 particles on leaf surfaces by scanning electron microscopy. In addition, the particle intake into an inner structure of leaves was studied by transmission electron microscopy. The effects of fine particle exposure and wind speed on emission rates of biogenic volatile organic compounds (BVOCs) were measured. Particles were captured (Cp) equally efficiently on foliage of B. pendula (0.0026 ± 0.0005) % and B. pubescens (0.0025 ± 0.0006) %. Increasing wind speed significantly decreased Cp. Increasing wind speed increased deposition velocity (Vg) on B. pendula but not on B. pubescens. Particles were deposited more efficiently on the underside of B. pendula leaves, whereas deposition was similar on the upper and under sides of B. pubescens leaves. TiO2 particles were found inside three of five B. pendula leaves exposed to particles at a wind speed of 1 ms−1 indicating that particles can penetrate into the plant structure. Emission rates of several mono-, homo- and sesquiterpenes were highest at a wind speed of 3 ms−1 in B. pendula. In B. pubescens, emission rates of a few monoterpenes and nonanal decreased linearly with wind speed, but emission rates of sesquiterpenes were lowest at 3 ms−1 and increased at 6 ms−1. Emission rates of a few green leaf volatile compounds increased with increasing wind speed in both species. The results of this study suggest that the surface structure of trees is less important for capturing particles with a diameter of ca 0.3 μm than for larger particles. Airborne fine particles penetrated into the intercellular space of the leaf via stomata, and this mechanism should be studied further for a better understanding of nanomaterial accumulation in nature. Wind can affect BVOC emissions and composition.
Keywords: Fine particles; BVOCs; Particle intake; Deposition; Birch; Wind speed;
Atmospheric behaviors of particulate-bound polycyclic aromatic hydrocarbons and nitropolycyclic aromatic hydrocarbons in Beijing, China from 2004 to 2010 by Ning Tang; Genki Suzuki; Hiroshi Morisaki; Takahiro Tokuda; Xiaoyang Yang; Lixia Zhao; Jinming Lin; Takayuki Kameda; Akira Toriba; Kazuichi Hayakawa (354-361).
Airborne particulates were collected at an urban site (site 1) from 2004 to 2010 and at a suburban site (site 2) in 2010 in Beijing. Nine polycyclic aromatic hydrocarbons (PAHs) and five nitropolycyclic aromatic hydrocarbons (NPAHs) in the airborne particulates were determined by HPLC with fluorescence and chemiluminescence detection, respectively. The concentrations of PAHs and NPAHs were higher in heating season than in non-heating season at the two sites. Both the concentrations of PAHs and NPAHs decreased in the non-heating season but only the concentrations of NPAHs decreased in heating season at site 1, from 2004 to 2010. These findings suggest that source control measures implemented by the city of Beijing helped to reduce air pollution in Beijing. The concentrations of PAHs increased at site 1 in 2010, possibly because of the transport of emissions from windward other areas, such as Shanxi province. Several diagnostic ratios of PAHs and NPAHs showed that the different sources contributed to Beijing's air pollution, although coal combustion was the main source in the heating season and vehicle emission was the main source in the non-heating season. An analysis of physical parameters at Beijing showed that high wind speed can remove atmospheric PAHs and NPAHs in the heating season and that high relative humidity can remove them in the non-heating season.
Keywords: PAHs; NPAHs; Air pollution; Source control measure; Beijing;
Impact of high-resolution sea surface temperature, emission spikes and wind on simulated surface ozone in Houston, Texas during a high ozone episode by Shuai Pan; Yunsoo Choi; Wonbae Jeon; Anirban Roy; David A. Westenbarger; Hyun Cheol Kim (362-376).
Model-measurement comparisons for surface ozone often show significant error, which could be attributed to problems in meteorology and emissions fields. A WRF-SMOKE-CMAQ air quality modeling system was used to investigate the contributions of these inputs. In this space, a base WRF run (BASE) and a WRF run initializing with NOAA GOES satellite sea surface temperature (SST) (SENS) were performed to clarify the impact of high-resolution SST on simulated surface ozone (O3) over the Greater Houston area during 25 September 2013, corresponding to the high O3 episode during the NASA DISCOVER-AQ Texas campaign. The SENS case showed reduced land-sea thermal contrast during early morning hours due to 1–2 °C lower SST over water bodies. The lowered SST reduced the model wind speed and slowed the dilution rate. These changes led to a simulated downwind O3 change of ∼5 ppb near the area over land with peak simulated afternoon O3. However, the SENS case still under-predicted surface O3 in urban and industrial areas. Episodic flare emissions, dry sunny postfrontal stagnated conditions, and land-bay/sea breeze transitions could be the potential causes of the high O3.In order to investigate the additional sources of error, three sensitivity simulations were performed for the high ozone time period. These involved adjusted emissions, adjusted wind fields, and both adjusted emissions and winds. These scenarios were superimposed on the updated SST (SENS) case. Adjusting NOx and VOC emissions using simulated/observed ratios improved correlation and index of agreement (IOA) for NOx from 0.48 and 0.55 to 0.81 and 0.88 respectively, but still reported spatial misalignment of afternoon O3 hotspots. Adjusting wind fields to represent morning weak westerly winds and afternoon converging zone significantly mitigated under-estimation of the observed O3 peak. For example, simulations with adjusted wind fields and adjusted (emissions + wind fields) reduced under-estimation of the peak magnitude of 100 ppb from 50 ppb to 7 and 9 ppb. Additionally, these sensitivity cases captured the timing and location of the observed O3 hotspots. The simulation case with both adjusted emissions and wind fields showed the best statistics for NOx (correlation: 0.84; IOA: 0.90) and O3 (correlation: 0.87; IOA: 0.92). These comparisons suggest that emissions and wind fields are important in determining the magnitude of high peaks, and wind direction is more critical in determining their timing and location. Particularly, improving the model capability to reproduce small-scale meteorological conditions favoring O3 production, such as stagnation and wind reversal, is crucial for accurate placement of locations of peak O3 and its precursors.
Keywords: SST; Emission; Wind direction; CMAQ; Ozone nonattainment; Houston;
Nitrous oxide emissions from soils amended by cover-crops and under plastic film mulching: Fluxes, emission factors and yield-scaled emissions by Gil Won Kim; Suvendu Das; Hyun Young Hwang; Pil Joo Kim (377-388).
Assessment of nitrous oxide (N2O) emission factor (EF) for N2O emission inventory from arable crops fertilized with different nitrogen sources are under increased scrutiny because of discrepancies between the default IPCC EFs and low EFs reported by many researchers. Mixing ratio of leguminous and non-leguminous cover crop residues incorporation and plastic film mulching (PFM) in upland soil has been recommended as a vital agronomic practice to enhance yield and soil quality. However, how these practices together affect N2O emissions, yield-scaled emissions and the EFs remain uncertain. Field experiments spanning two consecutive years were conducted to evaluate the effects of PFM on N2O emissions, yield-scaled emissions and the seasonal EFs in cover crop residues amended soil during maize cultivation. The mixture of barley (Hordeum vulgare) and hairy vetch (Vicia villosa) seeds with 75% recommended dose (RD 140 kg ha−1) and 25% recommended dose (RD 90 kg ha−1), respectively, were broadcasted during the fallow period and 0, 25, 50 and 100% of the total aboveground harvested biomass that correspond to 0, 76, 152 and 304 kg N ha−1 were incorporated before maize transplanting. It was found that the mean seasonal EFs from cover crop residues amended soil under No-mulching (NM) and PFM were 1.13% (ranging from 0.81 to 1.23%) and 1.49% (ranging from 1.02 to 1.63%), respectively, which are comparable to the IPCC (2006) default EF (1%) for emission inventories of N2O from crop residues. The emission fluxes were greatly influenced by NH4 + ―N, NO3 −-N, DOC and DON contents of soil. The cumulative N2O emissions markedly increased with the increase in cover crop residues application rates and it was more prominent under PFM than under NM. However, the yield-scaled emissions markedly decreased under PFM compared to NM due to the improved yield. With relatively low yield-scaled N2O emissions, 25% biomass mixing ratio of barley and hairy vetch (76 kg N ha−1) under PFM could be recommended to enhance yield and to mitigate N2O emissions in an upland maize cropping system.Display Omitted
Keywords: Nitrous oxide; Emission factors; Yield-scaled emissions; Plastic film mulching; Cover crop;
A modeling study on the effect of urban land surface forcing to regional meteorology and air quality over South China by Kuanguang Zhu; Min Xie; Tijian Wang; Junxiong Cai; Songbing Li; Wen Feng (389-404).
The change of land-use from natural to artificial surface induced by urban expansion can deeply impact the city environment. In this paper, the model WRF/Chem is applied to explore the effect of this change on regional meteorology and air quality over South China, where people have witnessed a rapid rate of urbanization. Two sets of urban maps are adopted to stand for the pre-urbanization and the present urban land-use distributions. Month-long simulations are conducted for January and July, 2014. The results show that urban expansion can obviously change the weather conditions around the big cities of South China. Especially in the Pearl River Delta region (PRD), the urban land-use change can increase the sensible heat flux by 40 W/m2 in January and 80 W/m2 in July, while decrease the latent heat flux about −50 W/m2 in January and −120 W/m2 in July. In the consequent, 2-m air temperature (T2) increases as much as 1 °C and 2 °C (respective to January and July), planetary boundary layer height (PBLH) rises up by 100–150 m and 300 m, 10-m wind speed (WS10) decreases by −1.2 m/s and −0.3 m/s, and 2-m specific humidity is reduced by −0.8 g/kg and −1.5 g/kg. Also, the precipitation in July can be increased as much as 120 mm, with more heavy rains and rainstorms. These variations of meteorological factors can significantly impact the spatial and vertical distribution of air pollutants as well. In PRD, the enhanced updraft can reduce the surface concentrations of PM10 by −40 μg/m3 (30%) in January and −80 μg/m3 (50%) in July, but produce a correlating increase in the concentrations at higher atmospheric layers. However, according to the increase in T2 and the decrease in surface NO, the surface concentrations of O3 in PRD can increase by 2–6 ppb in January and 8–12 ppb in July. Meanwhile, there is a significant increase in the O3 concentrations at upper layers above PRD, which should be attributed to the increase in air temperature and the enhanced upward transport of O3 and its precursors. As for some relative small cities, such as Haikou, there is very little variation in surface PM10 and O3 in both months, implying less urbanization in these areas. Moreover, the depletion of O3 by NO may be the main cause of the reduction of O3 at upper layers in these small cities.
Keywords: Urbanization; Land-use; South China; Meteorological conditions; Air quality; WRF/Chem;
Methanol emissions from maize: Ontogenetic dependence to varying light conditions and guttation as an additional factor constraining the flux by A. Mozaffar; N. Schoon; A. Digrado; A. Bachy; P. Delaplace; P. du Jardin; M.-L. Fauconnier; M. Aubinet; B. Heinesch; C. Amelynck (405-417).
Because of its high abundance and long lifetime compared to other volatile organic compounds in the atmosphere, methanol (CH3OH) plays an important role in atmospheric chemistry. Even though agricultural crops are believed to be a large source of methanol, emission inventories from those crop ecosystems are still scarce and little information is available concerning the driving mechanisms for methanol production and emission at different developmental stages of the plants/leaves. This study focuses on methanol emissions from Zea mays L. (maize), which is vastly cultivated throughout the world. Flux measurements have been performed on young plants, almost fully grown leaves and fully grown leaves, enclosed in dynamic flow-through enclosures in a temperature and light-controlled environmental chamber. Strong differences in the response of methanol emissions to variations in PPFD (Photosynthetic Photon Flux Density) were noticed between the young plants, almost fully grown and fully grown leaves. Moreover, young maize plants showed strong emission peaks following light/dark transitions, for which guttation can be put forward as a hypothetical pathway. Young plants’ average daily methanol fluxes exceeded by a factor of 17 those of almost fully grown and fully grown leaves when expressed per leaf area. Absolute flux values were found to be smaller than those reported in the literature, but in fair agreement with recent ecosystem scale flux measurements above a maize field of the same variety as used in this study. The flux measurements in the current study were used to evaluate the dynamic biogenic volatile organic compound (BVOC) emission model of Niinemets and Reichstein. The modelled and measured fluxes from almost fully grown leaves were found to agree best when a temperature and light dependent methanol production function was applied. However, this production function turned out not to be suitable for modelling the observed emissions from the young plants, indicating that production must be influenced by (an) other parameter(s). This study clearly shows that methanol emission from maize is complex, especially for young plants. Additional studies at different developmental stages of other crop species will be required in order to develop accurate methanol emission algorithms for agricultural crops.Display Omitted
Keywords: Maize; Methanol; VOC; Guttation; Emission modelling;
A three-year investigation of daily PM2.5 main chemical components in four sites: the routine measurement program of the Supersito Project (Po Valley, Italy) by Isabella Ricciardelli; Dimitri Bacco; Matteo Rinaldi; Giovanni Bonafè; Fabiana Scotto; Arianna Trentini; Giulia Bertacci; Pamela Ugolini; Claudia Zigola; Flavio Rovere; Claudio Maccone; Claudia Pironi; Vanes Poluzzi (418-430).
In all the sites, organic and elemental carbon and water soluble inorganic ions accounted for more than 70% of PM2.5 mass, during all seasons. Nitrate and organic carbon (OC) were the main components of winter PM2.5, while summer aerosol was mainly contributed by OC and sulphate. OC was dominated by primary sources, with a potentially important contribution from biomass burning, in winter, while secondary processes dominated OC production in summer.A substantial homogeneity was observed on a regional scale in terms of spatial distribution of pollutants, with EC only presenting significant differences between urban and rural areas during winters. Nonetheless, differences were observed between the coastal and the inner part of the region, with the former being systematically characterized by higher concentrations of carbonaceous compounds and lower concentrations of ammonium nitrate. The coastal area was likely influenced by the aged OC from the Po Valley outflow in addition to local sources, while the scarcity of local sources of ammonia limited the formation of ammonium nitrate.In the studied area, local and regional meteorology - mostly governed by geographical collocation and orography – was responsible for PM2.5 mass and composition no less than local and regional emission sources.
Keywords: PM2.5; Nitrate; Organic carbon; Elemental carbon; Po Valley;
Heating with Biomass in the United Kingdom: Lessons from New Zealand by E.J.S. Mitchell; G. Coulson; E.W. Butt; P.M. Forster; J.M. Jones; A. Williams (431-454).
In this study we review the current status of residential solid fuel (RSF) use in the UK and compare it with New Zealand, which has had severe wintertime air quality issues for many years that is directly attributable to domestic wood burning in heating stoves. Results showed that RSF contributed to more than 40 μg m−3 PM10 and 10 μg m−3 BC in some suburban locations of New Zealand in 2006, with significant air quality and climate impacts. Models predict RSF consumption in New Zealand to decrease slightly from 7 PJ to 6 PJ between 1990 and 2030, whereas consumption in the UK increases by a factor of 14. Emissions are highest from heating stoves and fireplaces, and their calculated contribution to radiative forcing in the UK increases by 23% between 2010 and 2030, with black carbon accounting for more than three quarters of the total warming effect. By 2030, the residential sector accounts for 44% of total BC emissions in the UK and far exceeds emissions from the traffic sector. Finally, a unique bottom-up emissions inventory was produced for both countries using the latest national survey and census data for the year 2013/14. Fuel- and technology-specific emissions factors were compared between multiple inventories including GAINS, the IPCC, the EMEP/EEA and the NAEI. In the UK, it was found that wood consumption in stoves was within 30% of the GAINS inventory, but consumption in fireplaces was substantially higher and fossil fuel consumption is more than twice the GAINS estimate. As a result, emissions were generally a factor of 2–3 higher for biomass and 2–6 higher for coal. In New Zealand, coal and lignite consumption in stoves is within 24% of the GAINS inventory estimate, but wood consumption is more than 7 times the GAINS estimate. As a result, emissions were generally a factor of 1–2 higher for coal and several times higher for wood. The results of this study indicate that emissions from residential heating stoves and fireplaces may be underestimated in climate models. Emissions are increasing rapidly in the UK which may result in severe wintertime air quality reductions, as seen in New Zealand, and contribute to climate warming unless controls are implemented such as the Ecodesign emissions limits.A delivery of wood logs to a home in South Island, New Zealand.Display Omitted
Keywords: Residential solid fuels; Emissions inventories; Climate;
Allergen aerosol from pollen-nucleated precipitation: A novel thunderstorm asthma trigger by Paul John Beggs (455-457).
Salt-marsh plants as potential sources of Hg0 into the atmosphere by João Canário; Laurier Poissant; Martin Pilote; Miguel Caetano; Holger Hintelmann; Nelson J. O'Driscoll (458-464).
To assess the role of salt-marsh plants on the vegetation-atmospheric Hg0 fluxes, three salt marsh plant species, Halimione portulacoides, Sarcocornia fruticosa and Spartina maritima were selected from a moderately contaminated site in the Tagus estuary during May 2012. Total mercury in stems and leaves for each plant as well as total gaseous mercury and vegetation-air Hg0 fluxes were measured over two continuous days. Mercury fluxes were estimated with a dynamic flux Tedlar® bag coupled to a high-resolution automated mercury analyzer (Tekran 2537A). Other environmental parameters such as air temperature, relative humidity and net solar radiation were also measured aside. H. portulacoides showed the highest total mercury concentrations in stems and leaves and the highest average vegetation-air Hg0 flux (0.48 ± 0.40 ng Hg m−2 h−1). The continuous measurements converged to a daily pattern for all plants, with enhanced fluxes during daylight and lower flux during the night. It is noteworthy that throughout the measurements a negative flux (air-vegetation) was never observed, suggesting the absence of net Hg0 deposition. Based on the above fluxes and the total area occupied by each species we have estimated the total amount of Hg0 emitted from this salt-marsh plants. A daily emission of 1.19 mg Hg d−1 was predicted for the Alcochete marsh and 175 mg Hg d−1 for the entire salt marsh area of the Tagus estuary.
Heterogeneous reaction of SO2 with soot: The roles of relative humidity and surface composition of soot in surface sulfate formation by Yan Zhao; Yongchun Liu; Jinzhu Ma; Qingxin Ma; Hong He (465-476).
The conversion of SO2 to sulfates on the surface of soot is still poorly understood. Soot samples with different fractions of unsaturated hydrocarbons and oxygen-containing groups were prepared by combusting n-hexane under well-controlled conditions. The heterogeneous reaction of SO2 with soot was investigated using in situ attenuated total internal reflection infrared (ATR-IR) spectroscopy, ion chromatography (IC) and a flow tube reactor at the ambient pressure and relative humidity (RH). Water promoted SO2 adsorption and sulfate formation at the RH range from 6% to 70%, while exceeded water condensed on soot was unfavorable for sulfate formation due to inhibition of SO2 adsorption when RH was higher than 80%. The surface composition of soot, which was governed by combustion conditions, also played an important role in the heterogeneous reaction of SO2 with soot. This effect was found to greatly depend on RH. At low RH of 6%, soot with the highest fuel/oxygen ratio of 0.162 exhibited a maximum uptake capacity for SO2 because it contained a large amount of aromatic C―H groups, which acted as active sites for SO2 adsorption. At RH of 54%, soot produced with a fuel/oxygen ratio of 0.134 showed the highest reactivity toward SO2 because it contained appropriate amounts of aromatic C―H groups and oxygen-containing groups, subsequently leading to the optimal surface concentrations of both SO2 and water. These results suggest that variation in the surface composition of soot from different sources and/or resulting from chemical aging in the atmosphere likely affects the conversion of SO2 to sulfates.Display Omitted
Keywords: Soot; SO2; Relative humidity; Surface composition; Sulfate formation;
Point-surface fusion of station measurements and satellite observations for mapping PM2.5 distribution in China: Methods and assessment by Tongwen Li; Huanfeng Shen; Chao Zeng; Qiangqiang Yuan; Liangpei Zhang (477-489).
Fine particulate matter (PM2.5, particulate matters with aerodynamic diameters less than 2.5 μ m ) is associated with adverse human health effects, and China is currently suffering from serious PM2.5 pollution. To obtain spatially continuous ground-level PM2.5 concentrations, several models established by the point-surface fusion of station measurements and satellite observations have been developed. However, how well do these models perform at national scale in China? Is there space to improve the estimation accuracy of PM2.5 concentration? The contribution of this study is threefold. Firstly, taking advantage of the newly established national monitoring network, we develop a national-scale generalized regression neural network (GRNN) model to estimate PM2.5 concentrations. Secondly, different assessment experiments are undertaken in time and space, to comprehensively evaluate and compare the performance of the widely used models. Finally, to map the yearly and seasonal mean distribution of PM2.5 concentrations in China, a pixel-based merging strategy is proposed. The results indicate that the conventional models (linear regression, multiple linear regression, and semi-empirical model) do not obtain the expected results at national scale, with cross-validation R values of 0.49–0.55 and RMSEs of 30.80–31.51 μ g / m 3 , respectively. In contrast, the more advanced models (geographically weighted regression, back-propagation neural network, and GRNN) have great advantages in PM2.5 estimation, with R values ranging from 0.61 to 0.82 and RMSEs from 20.93 to 28.68 μ g / m 3 , respectively. In particular, the proposed GRNN model obtains the best performance. Furthermore, the mapped PM2.5 distribution retrieved from 3-km MODIS aerosol optical depth (AOD) products agrees quite well with the station measurements. The results also show that the approach used in this study has the capacity to provide reasonable information for the global monitoring of PM2.5 pollution in China.
Keywords: Satellite remote sensing; Point-surface fusion; AOD; PM2.5; GRNN; Assessment;
Effects of inorganic seed aerosols on the particulate products of aged 1,3,5-trimethylbenzene secondary organic aerosol by Mingqiang Huang; Liqing Hao; Shunyou Cai; Xuejun Gu; Weixiong Zhang; Changjin Hu; Zhenya Wang; Li Fang; Weijun Zhang (490-502).
Inorganic aerosols such as (NH4)2SO4, NaNO3 and CaCl2 are commonly present in the Chinese urban atmosphere. They could significantly affect the formation and aging of ambient secondary organic aerosols (SOA), but the underlying mechanisms remain unknown. In this work we studied SOA formation from the photooxidation reaction of 1,3,5-trimethylbenzene (135-TMB) with 100 μg/m3 of the above three types of inorganic aerosols as seeds in a laboratory chamber. We focused on the aging products of SOA particles by exposing them to high levels of oxidizing hydroxyl radicals (OH). The particulate products of SOA were measured using an aerosol laser time-of-flight mass spectrometer (ALTOFMS) and Fuzzy C-Means (FCM) were applied to organic mass spectra for clustering. In the presence of (NH4)2SO4 seeds, 4-methyl-1H-imidazole, 4-methyl-imidazole-2-acetaldehyde and other imidazole derivative compounds formed from reactions of NH4 + with methylglyoxal were detected as new aged products. We also observed aromatic nitrogen-containing organic compounds as the major aged products in the presence of NaNO3 seeds as a consequence of reaction with OH and NO2 radicals, which were generated by UV irradiation of acidic aqueous nitrate, inducing nitration reactions with phenolic compounds. As CaCl2 has the strongest hygroscopic properties of the three salt particles tested, the greater water content on the surface of the aerosol may facilitate the condensing of more gas-phase organic acid products to the hygroscopic CaCl2 seeds, forming H+ ions that catalyze the heterogeneous reaction of aldehydes, products of photooxidation of 135-TMB, and forming high-molecular-weight (HMW) compounds. These results provide new insight into the aromatic SOA aging mechanisms.Display Omitted
Keywords: 1,3,5-trimethylbenzene; Inorganic seed aerosols; Secondary organic aerosol; Aerosol mass spectrometry; Aging mechanisms;
3D aerosol climatology over East Asia derived from CALIOP observations by Yongbo Zhou; Xuejin Sun; Chuanliang Zhang; Riwei Zhang; Yan Li; Haoran Li (503-518).
The seasonal mean extinction coefficient profile (ECP), single scattering albedo (SSA), and scattering phase function (SPF) derived from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) version 3 Level 2 5-km aerosol profile product (2011–2014) were compiled into a three-dimensional (3D) aerosol climatology for East Asia. The SSA and SPF were calculated as the weighted averages of the scattering properties of the CALIOP aerosol subtypes. The weights were set to the occurrence frequencies of the subtypes. The single scattering properties of each subtype were extrapolated from the volume-based size distribution and complex refractive indexes based on Mie calculations. For the high-loading episodes (aerosol optical depth ≥ 0.6), the exponential ECP structures were most frequently observed over the farmland and desert areas, along with the uplifted ECP structures over the marine and coastal areas. Besides the desert areas, high-loading episodes also occurred over areas with frequent agricultural and industry activities. Unlike the conventional half-3D aerosol climatology (vertically constant SSA and SPF), this newly generated climatology specified SSA and SPF in the full-3D space (full-3D aerosol climatology). Errors on the shortwave radiative heating rate (SW RHR) due to the half-3D aerosol climatology approximation were quantified. The SW RHR errors were around ±1 K/day, implying that the half-3D aerosol climatology should be used with caution in climate modeling. This study is among the first to generate a full-3D aerosol climatology from the CALIOP data. This full-3D aerosol climatology is potentially useful for aerosol remote sensing and climate modeling.
Keywords: 3D aerosol climatology; CALIOP; The East Asia; Radiative heating rate;
Evaluation of Bayesian source estimation methods with Prairie Grass observations and Gaussian plume model: A comparison of likelihood functions and distance measures by Yan Wang; Hong Huang; Lida Huang; Branko Ristic (519-530).
Source term estimation for atmospheric dispersion deals with estimation of the emission strength and location of an emitting source using all available information, including site description, meteorological data, concentration observations and prior information. In this paper, Bayesian methods for source term estimation are evaluated using Prairie Grass field observations. The methods include those that require the specification of the likelihood function and those which are likelihood free, also known as approximate Bayesian computation (ABC) methods. The performances of five different likelihood functions in the former and six different distance measures in the latter case are compared for each component of the source parameter vector based on Nemenyi test over all the 68 data sets available in the Prairie Grass field experiment. Several likelihood functions and distance measures are introduced to source term estimation for the first time. Also, ABC method is improved in many aspects. Results show that discrepancy measures which refer to likelihood functions and distance measures collectively have significant influence on source estimation. There is no single winning algorithm, but these methods can be used collectively to provide more robust estimates.
Keywords: Bayesian inference; Source estimation; Approximate Bayesian computation; Markov chain Monte Carlo; Sequential Monte Carlo; Prairie Grass field experiment;
Impact of future climate policy scenarios on air quality and aerosol-cloud interactions using an advanced version of CESM/CAM5: Part II. Future trend analysis and impacts of projected anthropogenic emissions by Timothy Glotfelty; Yang Zhang (531-552).
Following a comprehensive evaluation of the Community Earth System Model modified at the North Carolina State University (CESM-NCSU), Part II describes the projected changes in the future state of the atmosphere under the representative concentration partway scenarios (RCP4.5 and 8.5) by 2100 for the 2050 time frame and examine the impact of climate change on future air quality under both scenarios, and the impact of projected emission changes under the RCP4.5 scenario on future climate through aerosol direct and indirect effects. Both the RCP4.5 and RCP8.5 simulations predict similar changes in air quality by the 2050 period due to declining emissions under both scenarios. The largest differences occur in O3, which decreases by global mean of 1.4 ppb under RCP4.5 but increases by global mean of 2.3 ppb under RCP8.5 due to differences in methane levels, and PM10, which decreases by global mean of 1.2 μg m−3 under RCP4.5 and increases by global mean of 0.2 μg m−3 under RCP8.5 due to differences in dust and sea-salt emissions under both scenarios. Enhancements in cloud formation in the Arctic and Southern Ocean and increases of aerosol optical depth (AOD) in central Africa and South Asia dominate the change in surface radiation in both scenarios, leading to global average dimming of 1.1 W m−2 and 2.0 W m−2 in the RCP4.5 and RCP8.5 scenarios, respectively. Declines in AOD, cloud formation, and cloud optical thickness from reductions of emissions of primary aerosols and aerosol precursors under RCP4.5 result in near surface warming of 0.2 °C from a global average increase of 0.7 W m−2 in surface downwelling solar radiation. This warming leads to a weakening of the Walker Circulation in the tropics, leading to significant changes in cloud and precipitation that mirror a shift in climate towards the negative phase of the El Nino Southern Oscillation.
Keywords: CESM/CAM5; Representative concentration pathways; Global climate change; Future air quality; Climate change; Emission changes;
Generation and UV-VIS-NIR spectral responses of organo-mineral aerosol for modelling soil derived dust by N. Utry; T. Ajtai; M. Pintér; E. Illés; E. Tombácz; G. Szabó; Z. Bozóki (553-561).
Various optical properties of laboratory constructed clay minerals coated by humic acid were determined in this study. For the preparation of organo-clay complexes, an adsorption method was conducted in Ca2+ dominated aquaeous solutions, which provides the opportunity to generate solely internally mixed aerosol particles with complete surface covering. The wavelength dependent optical absorption and scattering coefficients of the syntetised organo-clay complexes and the single clay components were measured in-situ in aerosol phase, using multi-wavelength photoacoustic and scattering instruments. Other climate relevant optical properties such as mass absorption and scattering coefficients, absorption enhancement factor, the imaginary part of complex refractive index, single scattering albedo and coating thickness were also deduced from the measured data. The estimated thickness of humic acid coating was about 10–20 nm. Even such relatively thin shell substantially enhanced the measured absorption of the clay particles with an enhancement factor of about 3–7 in the visible-near ultraviolet range, while caused smaller changes in the mass scattering values. As a cumulative effect, the coating decreased the single scattering albedo of the clay particles; from 0.99 ± 0.04 to 0.93 ± 0.04 in case of illite and from 0.99 ± 0.04 to 0.90 ± 0.03 in case of kaolin at 525 nm. The HA coating slightly modified the shape, the particles became less excentric. We presented a new method capable of generating solely internally mixed particles. Applying this method we experimentally demonstrated the strong effect of a light absorbing coating on the optical properties of dust particle.
Keywords: Mineral dust; Photoacoustic spectroscopy; Optical absorption; Enhancement factor; Humic acid; Soil organic matter;
Decadal application of WRF/Chem for regional air quality and climate modeling over the U.S. under the representative concentration pathways scenarios. Part 1: Model evaluation and impact of downscaling by Khairunnisa Yahya; Kai Wang; Patrick Campbell; Ying Chen; Timothy Glotfelty; Jian He; Michael Pirhalla; Yang Zhang (562-583).
An advanced online-coupled meteorology-chemistry model, i.e., the Weather Research and Forecasting Model with Chemistry (WRF/Chem), is applied for current (2001–2010) and future (2046–2055) decades under the representative concentration pathways (RCP) 4.5 and 8.5 scenarios to examine changes in future climate, air quality, and their interactions. In this Part I paper, a comprehensive model evaluation is carried out for current decade to assess the performance of WRF/Chem and WRF under both scenarios and the benefits of downscaling the North Carolina State University's (NCSU) version of the Community Earth System Model (CESM_NCSU) using WRF/Chem. The evaluation of WRF/Chem shows an overall good performance for most meteorological and chemical variables on a decadal scale. Temperature at 2-m is overpredicted by WRF (by ∼0.2–0.3 °C) but underpredicted by WRF/Chem (by ∼0.3–0.4 °C), due to higher radiation from WRF. Both WRF and WRF/Chem show large overpredictions for precipitation, indicating limitations in their microphysics or convective parameterizations. WRF/Chem with prognostic chemical concentrations, however, performs much better than WRF with prescribed chemical concentrations for radiation variables, illustrating the benefit of predicting gases and aerosols and representing their feedbacks into meteorology in WRF/Chem. WRF/Chem performs much better than CESM_NCSU for most surface meteorological variables and O3 hourly mixing ratios. In addition, WRF/Chem better captures observed temporal and spatial variations than CESM_NCSU. CESM_NCSU performance for radiation variables is comparable to or better than WRF/Chem performance because of the model tuning in CESM_NCSU that is routinely made in global models.
Keywords: WRF/Chem; WRF; CESM; The continental U.S.; Decadal evaluation; Air quality-climate interactions;
Decadal application of WRF/chem for regional air quality and climate modeling over the U.S. under the representative concentration pathways scenarios. Part 2: Current vs. future simulations by Khairunnisa Yahya; Patrick Campbell; Yang Zhang (584-604).
Following a comprehensive model evaluation, this Part II paper presents projected changes in future (2046–2055) climate, air quality, and their interactions under the RCP4.5 and RCP8.5 scenarios using the Weather, Research and Forecasting model with Chemistry (WRF/Chem). In general, both WRF/Chem RCP4.5 and RCP8.5 simulations predict similar increases on average (∼2 °C) for 2-m temperature (T2) but different spatial distributions of the projected changes in T2, 2-m relative humidity, 10-m wind speed, precipitation, and planetary boundary layer height, due to differences in the spatial distributions of projected emissions, and their feedbacks into climate. Future O3 mixing ratios will decrease for most parts of the U.S. under the RCP4.5 scenario but increase for all areas under the RCP8.5 scenario due to higher projected temperature, greenhouse gas concentrations and biogenic volatile organic compounds (VOC) emissions, higher O3 values for boundary conditions, and disbenefit of NOx reduction and decreased NO titration over VOC-limited O3 chemistry regions. Future PM2.5 concentrations will decrease for both RCP4.5 and RCP8.5 scenarios with different trends in projected concentrations of individual PM species. Total cloud amounts decrease under both scenarios in the future due to decreases in PM and cloud droplet number concentration thus increased radiation. Those results illustrate the impacts of carbon policies with different degrees of emission reductions on future climate and air quality. The WRF/Chem and WRF simulations show different spatial patterns for projected changes in T2 for future decade, indicating different impacts of prognostic and prescribed gas/aerosol concentrations, respectively, on climate change.
Keywords: WRF/Chem; The representative concentration pathways (RCP) scenarios; Trend analysis; Future air quality; Continental U.S.; Air quality-climate interactions;
Large-eddy simulation of dense gas dispersion over a simplified urban area by E.M.M. Wingstedt; A.N. Osnes; E. Åkervik; D. Eriksson; B.A. Pettersson Reif (605-616).
Dispersion of neutral and dense gas over a simplified urban area, comprising four cubes, has been investigated by the means of large-eddy simulations (LES). The results have been compared to wind tunnel experiments and both mean and fluctuating quantities of velocity and concentration are in very good agreement.High-quality inflow profiles are necessary to achieve physically realistic LES results. In this study, profiles matching the atmospheric boundary layer flow in the wind tunnel, are generated by means of a separate precursor simulation.Emission of dense gas dramatically alters the flow in the near source region and introduces an upstream dispersion. The resulting dispersion patterns of neutral and dense gas differ significantly, where the plume in the latter case is wider and shallower. The dense gas is highly affected by the cube array, which seems to act as a barrier, effectively deflecting the plume. This leads to higher concentrations outside of the array than inside. On the contrary, the neutral gas plume has a Gaussian-type shape, with highest concentrations along the centreline.It is found that the dense gas reduces the vertical and spanwise turbulent momentum transport and, as a consequence, the turbulence kinetic energy. The reduction coincides with the area where the gradient Richardson number exceeds its critical value, i.e. where the flow may be characterized as stably stratified. Interestingly, this region does not correspond to where the concentration of dense gas is the highest (close to the ground), as this is also where the largest velocity gradients are to be found. Instead there is a layer in the middle of the dense gas cloud where buoyancy is dynamically dominant.
Keywords: LES; Wind tunnel; Dispersion; Dense gas; Urban flow; Atmospheric boundary layer;
Environmental studies in two communes of Santiago de Chile by the analysis of magnetic properties of particulate matter deposited on leaves of roadside trees by David Muñoz; Bertha Aguilar; Raúl Fuentealba; Margarita Préndez (617-627).
Emissions from motor vehicles are considered to be one of the main sources of airborne particulate matter in Santiago. International researchers have shown that particulate matter contains metal oxides and magnetic particles, both of which are emitted mainly from vehicles exhaust pipes. On the other hand, trees are effective in reducing such contamination, so that they act as passive collectors of particulate matter. This work presents the results obtained from the first magnetic study of the particulate matter collected in two areas of the city of Santiago de Chile. Magnetic susceptibility and Saturation Isothermic Remanent Magnetization (SIRM) were determined in leaves from abundant urban trees and from urban dust samples. Results indicate that most of the samples contain ferromagnetic minerals with magnetite (Fe3O4) as the main carrier. Values of magnetic susceptibility (SI ×10−6 m3/kg) in the range 0.04–0.24 for leaves and in the range 10–45 for urban dust were determinated. In one of the city areas studied, significant correlation between the particulate matter deposited on leaves of Platanus orientalis and measured traffic flows was obtained. In addition, it was possible to estimate that the species Platanus orientalis and Acer negundo have a better ability to capture particulate matter than the species Robinia pseudoacacia.
Keywords: Airborne particulate matter capture; Urban trees; Magnetic measurements; Traffic flows; Santiago de Chile;