Atmospheric Environment (v.131, #C)
Editorial board (i).
Characteristics of atmospheric CO2 and CH4 at the Shangdianzi regional background station in China by Shuang-xi Fang; Pieter P. Tans; Fan Dong; Huaigang Zhou; Tian Luan (1-8).
Atmospheric CO2 and CH4 have been continuously measured at the Shangdianzi regional background station (SDZ) in China from 2009 to 2013. Based on the influences of local surface wind and long-distance transport, the observed records were flagged into locally influenced, Beijing-Tianjin-Hebei (BTH) influenced, and Russia, Mongolia, and Inner Mongolia autonomous region influenced (RMI). ∼ 81.4% of CO2 and ∼75.6% of CH4 mole fractions were flagged as locally representative, indicating that the atmospheric CO2 and CH4 at SDZ were strongly influenced by local sources and sinks. Cluster analysis of back trajectories proved that the atmospheric CO2 and CH4 were influenced by air masses from northwest (RMI) or from south and southeast (BTH). The CO2 and CH4 mole fractions in BTH are always higher than in RMI, with the largest difference of 11.5 ± 0.3 ppm for CO2 and 102 ± 1 ppb for CH4 in July. The annual growth rates of CO2 and CH4 in BTH are 3.8 ± 0.01 ppm yr−1 and 10 ± 0.1 ppb yr−1, respectively, which are apparently higher than those of the RMI and the global means. The long-term trends of CO2 and CH4 in BTH are deviating from those in RMI, with ratios of ∼1.0 ppm yr−1 for CO2 and ∼2 ppb yr−1 for CH4, indicating the strengths of CO2 and CH4 emission in Beijing-Tianjin-Hebei plain increased more than 20% every year.Display Omitted
Keywords: Carbon dioxide; Methane; Observation; Back trajectory; Air mass transport;
A lack of consensus in the literature findings on the removal of airborne benzene by houseplants: Effect of bacterial enrichment by Wararat Sriprapat; Stuart E. Strand (9-16).
Removal rates of benzene and formaldehyde gas by houseplants reported by several laboratories varied by several orders of magnitude. We hypothesized that these variations were caused by differential responses of soil microbial populations to the high levels of pollutant used in the studies, and tested responses to benzene by plants and soils separately. Five houseplant species and tobacco were exposed to benzene under hydroponic conditions and the uptake rates compared. Among the test plants, Syngonium podophyllum and Chlorophytum comosum and Epipremnum aureum had the highest benzene removal rates. The effects of benzene addition on populations of soil bacteria were determined using reverse transcription quantitative PCR (RT-qPCR) assays targeting microbial genes involved in benzene degradation. The total bacterial population increased as shown by increases in the levels of eubacteria 16S rRNA, which was significantly higher in the high benzene incubations than in the low benzene incubations. Transcripts (mRNA) of genes encoding phenol monooxygenases, catechol-2,3-dioxygenase and the housekeeping gene rpoB increased in all soils incubated with high benzene concentrations. Therefore the enrichment of soils with benzene gas levels typical of experiments with houseplants in the literature artificially increased the levels of total soil bacterial populations, and especially the levels and activities of benzene-degrading bacteria.
Keywords: Benzene; Hydroponic; Phytoremediation; Soil microbial; Volatile organic compounds; Formaldehyde;
Mid-twentieth century increases in anthropogenic Pb, Cd and Cu in central Asia set in hemispheric perspective using Tien Shan ice core by B. Grigholm; P.A. Mayewski; V. Aizen; K. Kreutz; C.P. Wake; E. Aizen; S. Kang; K.A. Maasch; M.J. Handley; S.B. Sneed (17-28).
High-resolution major and trace element (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Li, Mn, Na, Pb, S, Ti, and V) ice core records from Inilchek glacier (5120 m above sea level) on the northwestern margin of the Tibetan Plateau provide the first multi-decadal ice core record spanning the period 1908–1995 AD in central Tien Shan. The trace element records reveal pronounced temporal baseline trends and concentration maxima characteristic of post-1950 anthropogenic emissions. Examination of Pb, Cd and Cu concentrations, along with non-crustal calculation estimates (i.e. excess (ex) and enrichment factor (EF)), reveal that discernable anthropogenic inputs began during the 1950s and rapidly increased to the late-1970s and early 1980s, by factors up to of 5, 6 and 3, respectively, relative to a 1910–1950 means. Pb, Cd and Cu concentrations between the 1950s-1980s are reflective of large-scale Soviet industrial and agricultural development, including the growth of production and/or consumption of the non-ferrous metals, coal and phosphate fertilizers. NOAA HYSPLIT back-trajectory frequency analysis suggests pollutant sources originating primarily from southern Kazakhstan (e.g. Shymkent and Balkhash) and the Fergana Valley (located in Kazakhstan, Uzbekistan and Kyrgyzstan). Inilchek ice core Pb, Cd and Cu reveals declines during the 1980s concurrent with Soviet economic declines, however, due to the rapid industrial and agricultural growth of western China, Pb, Cd and Cu trends increase during the 1990s reflecting a transition from primarily central Asian sources to emission sources from western China (e.g. Xinjiang Province).
Keywords: Ice core; Element; Pollution; Central Asia; Tien Shan;
Sensitivity analysis of ground level ozone in India using WRF-CMAQ models by Sumit Sharma; Satoru Chatani; Richa Mahtta; Anju Goel; Atul Kumar (29-40).
Ground level ozone is emerging as a pollutant of concern in India. Limited surface monitoring data reveals that ozone concentrations are well above the prescribed national standards. This study aims to simulate the regional and urban scale ozone concentrations in India using WRF-CMAQ models. Sector-specific emission inventories are prepared for the ozone precursor species at a finer resolution (36 × 36 km2) than used in previous studies. Meteorological fields developed using the WRF model are fed into the CMAQ model along with the precursor emissions to simulate ozone concentrations at a regional scale. The model is validated using observed ozone dataset. Sensitivity analysis is carried out to understand the effect of different precursor species and sources on prevailing ozone concentrations in India. The results show that NOx sensitive conditions prevail in India and control of NOx will result in more reduction in ozone than VOCs. However, further growth in the transport and power sector and decreasing VOC emissions from the residential sector may increase the sensitivity of VOCs towards ozone in the future. At the urban scale, presence of high NOx emissions form VOC limited conditions and reduction of NOx results in increase in ozone concentrations. However, this will help in improving regional scale ozone pollution in the downwind regions. A non-linear response has been observed while assessing the sectoral sensitivities of ozone formation. Transport sector is found to have the maximum potential for reducing ozone concentrations in India.
Keywords: Ozone; India; WRF-CMAQ; Sensitivity;
Total OH reactivity measurement in a BVOC dominated temperate forest during a summer campaign, 2014 by Sathiyamurthi Ramasamy; Akira Ida; Charlotte Jones; Shungo Kato; Hiroshi Tsurumaru; Iori Kishimoto; Shio Kawasaki; Yasuhiro Sadanaga; Yoshihiro Nakashima; Tomoki Nakayama; Yutaka Matsumi; Michihiro Mochida; Sara Kagami; Yange Deng; Shuhei Ogawa; Kaori Kawana; Yoshizumi Kajii (41-54).
A total OH reactivity measurement was conducted in coniferous forest located in Wakayama prefecture, Japan, during the summer of 2014. The average total OH reactivity, measured using a laser-induced pump and probe technique was 7.1 s−1. The measured OH reactivity was comparable with other coniferous and temperate forest measurements and much lower than that of tropical forests. OH reactivity varied diurnally and showed moderate linear correlation with temperature (r 2 = 0.66) and light (r 2 = 0.53). Monoterpene emitters, Cryptomeria japonica and Chamaecyparis obutsa, are the dominant tree species in this forest. Although clean air from the sea was predominant, the beginning of the campaign was influenced by transported anthropogenic pollutants and consequently a higher average OH reactivity of 9.8 s−1 with high missing sinks of 37.3% was determined. Cleaner conditions, along with cooler day-time temperatures during in the second half of the campaign resulted in a lower average OH reactivity of 6.0 s−1 with a lower missing OH reactivity of 21.5%. Monoterpenes, isoprene, acetaldehyde were the dominant contributors to the total OH reactivity, accounting for 23.7%, 17.0% and 14.5%, respectively.
Keywords: Total OH reactivity; Biogenic VOCs; Coniferous forest; Missing OH reactivity;
Ammonia emissions in Europe, part I: Development of a dynamical ammonia emission inventory by Anna Backes; Armin Aulinger; Johannes Bieser; Volker Matthias; Markus Quante (55-66).
Nitrogen input from agricultural ammonia emissions into the environment causes numerous environmental and health problems. The purpose of this study is to present and evaluate an improved ammonia emission inventory based on a dynamical temporal parameterization suitable to compare and assess ammonia abatement strategies. The setup of the dynamical time profile (DTP) consists of individual temporal profiles for ammonia emissions, calculated for each model grid cell, depending on temperature, crop type, fertilizer and manure application, as well as on local legislation. It is based on the method of Skjøth et al., 2004 and Gyldenkærne et al., 2005. The method has been modified to cover the study area and to improve the performance of the emission model. To compare the results of the dynamical approach with the results of the static time profile (STP) the ammonia emission parameterizations have been implemented in the SMOKE for Europe emission model. Furthermore, the influence on secondary aerosol formation in the North Sea region and possible changes triggered through the use of a modified temporal distribution of ammonia emissions were analysed with the CMAQ chemistry transport model. The results were evaluated with observations of the European Monitoring and Evaluation Programme (EMEP). The correlation coefficient of NH3 improved significantly for 12 out of 16 EMEP measurement stations and an improvement in predicting the Normalized Mean Error can be seen for particulate NH4 + and NO3 −. The prediction of the 95th percentile of the daily average concentrations has improved for NH3, NH4 + and NO3 −. The NH3 concentration modelled with the STP is 157% higher in winter, and about 22% lower in early summer than the one modelled with the new DTP. Consequently, the influence of the DTP on the formation of secondary aerosols is particularly noticeable in winter, when the PM2.5 concentration is 25% lower in comparison to the use of STP for temporal disaggregation. Besides, the formation of particulate SO4 2− is not influenced by the use of the DTP.
Simulating the phase partitioning of NH3, HNO3, and HCl with size-resolved particles over northern Colorado in winter by James T. Kelly; Kirk R. Baker; Christopher G. Nolte; Sergey L. Napelenok; William C. Keene; Alexander A.P. Pszenny (67-77).
Numerical modeling of inorganic aerosol processes is useful in air quality management, but comprehensive evaluation of modeled aerosol processes is rarely possible due to the lack of comprehensive datasets. During the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) campaign in February and March 2011, the phase partitioning of soluble trace gases with size-resolved particles and related meteorological conditions were measured continuously at a site in Colorado about 33 km north of Denver. These size-resolved measurements of particulate SO 4 2 − , NH 4 + , NO 3 − , Cl−, Na+, Ca2+, Mg2+, and K+ and inorganic gases are used here to assess the ability of a continental U.S. modeling platform to simulate the gas-particle partitioning of NH3, HNO3, and HCl at this location. Modeling is based on the Community Multiscale Air Quality (CMAQ) model with 12 km horizontal resolution. Baseline, sensitivity, and source apportionment simulations are conducted to fully characterize the model predictions. Considering the limitations in representing regional terrain features in the national 12 km modeling, predictions agree reasonably well with measured concentrations and gas-particle partitioning at this location. However, the median sum of NH 4 + and NH3 is underpredicted in the baseline simulation by a factor of four suggesting a need for improved bottom-up NH3 emissions inventories in this area. The median sum of Cl− and HCl is underpredicted by a factor of 2.8, while levels of Ca2+, Mg2+, and K+ are overpredicted. Improvements in windblown and fugitive dust emissions may improve and/or better constrain these predictions. Mass size distributions for inorganic particle constituents are generally simulated well, although the modeled fine particle mode is shifted to slightly larger diameters relative to measurements. Source apportionment modeling estimates of source sector and boundary contributions to air quality at the site are provided.
Keywords: Aerosol size distributions; Source apportionment; NACHTT;
Modeling the effect of relative humidity on nitrous acid formation in the Houston area by Lijun Diao; Anirban Roy; Beata Czader; Shuai Pan; Wonbae Jeon; Amir Hossein Souri; Yunsoo Choi (78-82).
The field and laboratory based relative humidity (RH) impact on nitrous acid (HONO) heterogeneous reaction has not been considered in chemical transport models. This study parameterized this dependency into the Community Multiscale Air Quality (CMAQ) model. In view of the positive linear correlation between the reaction rate and RH, the HONO heterogeneous reaction rate constants were respectively scaled by the factors of RH/30 and RH/40. Two corresponding sensitivity tests were carried out in the period of September 2013 in Houston. Both tests significantly improved modeled HONO concentrations and reduced the bias for NO2 in comparison with observations. However, the model is still not capable of reproducing the high HONO concentrations in the morning rush hours. Further work is needed to explore the underlying mechanisms for the early morning HONO formation.
Keywords: Nitrous acid; Relative humidity; CMAQ; DISCOVER-AQ; NO2;
Ammonia emission time profiles based on manure transport data improve ammonia modelling across north western Europe by C. Hendriks; R. Kranenburg; J.J.P. Kuenen; B. Van den Bril; V. Verguts; M. Schaap (83-96).
Accurate modelling of mitigation measures for nitrogen deposition and secondary inorganic aerosol (SIA) episodes requires a detailed representation of emission patterns from agriculture. In this study the meteorological influence on the temporal variability of ammonia emissions from livestock housing and application of manure and fertilizer are included in the chemistry transport model LOTOS-EUROS. For manure application, manure transport data from Flanders (Belgium) were used as a proxy to derive the emission variability. Using improved ammonia emission variability strongly improves model performance for ammonia, mainly by a better representation of the spring maximum. The impact on model performance for SIA was negligible as explained by the limited, ammonia rich region in which the emission variability was updated. The contribution of Flemish agriculture to modelled annual mean ammonia and SIA concentrations in Flanders were quantified at respectively 7–8 and 1–2 μg/m3. A scenario study was performed to investigate the effects of reducing ammonia emissions from manure application during PM episodes by 75%, yielding a maximum reduction in modelled SIA levels of 1–3 μg/m3 during episodes. Year-to-year emission variability and a soil module to explicitly model the emission process from manure and fertilizer application are needed to further improve the modelling of the ammonia budget.
Keywords: Ammonia; Air pollution; Emission timing; Source attribution; LOTOS-EUROS;
Highly buoyant bent-over plumes in a boundary layer by Ali Tohidi; Nigel B. Kaye (97-114).
Highly buoyant plumes, such as wildfire plumes, in low to moderate wind speeds have initial trajectories that are steeper than many industrial waste plumes. They will rise further into the atmosphere before bending significantly. In such cases the plume's trajectory will be influenced by the vertical variation in horizontal velocity of the atmospheric boundary layer. This paper examined the behavior of a plume in an unstratified environment with a power-law ambient velocity profile. Examination of previously published experimental measurements of plume trajectory show that inclusion of the boundary layer velocity profile in the plume model often provides better predictions of the plume trajectory compared to algebraic expressions developed for uniform flow plumes. However, there are many cases in which uniform velocity profile algebraic expressions are as good as boundary layer models. It is shown that it is only important to model the role of the atmospheric boundary layer velocity profile in cases where either the momentum length (square root of source momentum flux divided by the reference wind speed) or buoyancy length (buoyancy flux divided by the reference wind speed cubed) is significantly greater than the plume release height within the boundary layer. This criteria is rarely met with industrial waste plumes, but it is important in modeling wildfire plumes.
Keywords: Plume; Bent-over plume; Highly buoyant plume; Fire plume; Wildfire; Near source behavior;
Characterization of submicron aerosols at a suburban site in central China by Qingqing Wang; Jian Zhao; Wei Du; Godson Ana; Zhenzhu Wang; Lu Sun; Yuying Wang; Fang Zhang; Zhanqing Li; Xingnan Ye; Yele Sun (115-123).
We have characterized the chemical composition and sources of submicron aerosol (PM1) at a suburban site in Xinzhou in central China using an Aerosol Chemical Speciation Monitor from July 17 to September 5, 2014. The average (±1σ) PM1 concentration was 35.4 (±20.8) μg/m3 for the entire study period, indicating that Xinzhou was less polluted compared to the megacities in the North China Plain (NCP). The PM1 was mainly composed of organic aerosol and sulfate, on average accounting for 33.1% and 32.4%, respectively, followed by nitrate (14.4%) and ammonium (11.8%). Higher sulfate and lower nitrate contributions than those in megacities in the NCP elucidated an important emission source of coal combustion in central China. Three organic aerosol (OA) factors, i.e., hydrocarbon-like OA (HOA), semi-volatile oxygenated OA (SV-OOA) and low-volatility OOA (LV-OOA), were identified using positive matrix factorization. Secondary OA (=SV-OOA + LV-OOA) dominated OA, on average accounting for 82%, indicating that OA at the Xinzhou site was overall oxidized. We also observed relatively similar aerosol bulk composition and OA composition at low and high mass loading periods, and also from the different source areas, indicating that aerosol species were homogeneously distributed over a regional scale near the site for most of the time during this study. Slightly higher mass concentrations and sulfate contributions from the southern air masses were likely due to the transport from the polluted cities, such as Taiyuan to the south. In addition, the daily variation of PM1 in Xinzhou resembled that observed in Beijing, indicating that the wide-scale regional haze pollution often influences both the NCP and the central China.
Keywords: Submicron aerosol; Organic aerosol; Composition; Sources; Central China;
Atmospheric mercury at an urban station in Korea across three decades by Ki-Hyun Kim; Richard J.C. Brown; Eilhann Kwon; Ik-Soo Kim; Jong-Ryeul Sohn (124-132).
The concentrations of total gaseous mercury (TGM) over three decades (1987–2013) were monitored at an urban station at Yan San (YS), Seoul, Korea. The results were examined by considering the prominent patterns in observed concentrations during periods where data were available:  period I (P1) = Sep. 1987 to Oct. 1988,  period II (P2) = Sep. 1999 to Jul. 2000,  period III (P3) = Jan. 2004 to Dec. 2011, and  period IV (P4) = Jan. 2012 to Dec. 2013. The data in this study indicate that the concentrations of TGM decreased abruptly from P1 (∼15 ng m−3) to P2 (∼5 ng m−3). Then, during the most of P3 (i.e., from 2004 to 2011), the annual mean values were nearly constant and their concentrations were in the range 3–4 ng m−3. The mean values then decreased to ∼2 ng m−3 in P4. Hg levels in the late 1980s reflect the dominant role of major man-made source processes (e.g., unabated combustion of much dirtier fossil fuels). Unlike the earlier Hg monitoring data, the concentrations of Hg in recent periods could be attributed to a shift from coal to kerosene and natural gas in urban areas and to more stringent emissions regulations and cleaner fuels. It is unclear currently whether the latest and lowest concentrations measured during in P4 will be maintained during upcoming years, although they seem to reflect the direct impact of air quality control efforts since the 1980s.
Keywords: Anthropogenic; Urban; Residence time; Source signatures; Mercury;
Heterogeneous reactions of glyoxal on mineral particles: A new avenue for oligomers and organosulfate formation by Xiaoli Shen; Huihui Wu; Yue Zhao; Dao Huang; Liubin Huang; Zhongming Chen (133-140).
Glyoxal (GL) plays a crucial role in the formation of secondary organic aerosols (SOA), because it is highly water soluble and capable of oligomerization. This is the first study to describe irreversible heterogeneous reactions of GL on clean and acidic gas-aged SiO2, α-Al2O3, and CaCO3 particles, as models of real mineral particles, at various relative humidity and without irradiation and gas phase oxidants. A series of products, including oligomers, organosulfates, and organic acids, which contribute to SOA formation, were produced. GL uptake on SO2-aged α-Al2O3 enabled the oxidation of surface S(IV) to S(VI). The presence of adsorbed water on particles favored GL uptake and the formation of oligomers and organosulfate, but it suppressed organic acid formation. In addition, the aging process enhanced the positive effect of adsorbed water on GL uptake. These findings will further our understanding of the GL sink and SOA sources in the atmosphere.
Keywords: Glyoxal; Heterogeneous reaction; Mineral particle; Oligomer; Organosulfate;
PM2.5 and ultrafine particulate matter emissions from natural gas-fired turbine for power generation by Eli Brewer; Yang Li; Bob Finken; Greg Quartucy; Lawrence Muzio; Al Baez; Mike Garibay; Heejung S. Jung (141-149).
The generation of electricity from natural gas-fired turbines has increased more than 200% since 2003. In 2007 the South Coast Air Quality Management District (SCAQMD) funded a project to identify control strategies and technologies for PM2.5 and ultrafine emissions from natural gas-fired turbine power plants and test at pilot scale advanced PM2.5 technologies to reduce emissions from these gas turbine-based power plants. This prompted a study of the exhaust from new facilities to better understand air pollution in California. To characterize the emissions from new natural gas turbines, a series of tests were performed on a GE LMS100 gas turbine located at the Walnut Creek Energy Park in August 2013. These tests included particulate matter less than 2.5 μm in diameter (PM2.5) and wet chemical tests for SO2/SO3 and NH3, as well as ultrafine (less than 100 nm in diameter) particulate matter measurements. After turbine exhaust was diluted sevenfold with filtered air, particle concentrations in the 10–300 nm size range were approximately two orders of magnitude higher than those in the ambient air and those in the 2–3 nm size range were up to four orders of magnitude higher. This study also found that ammonia emissions were higher than expected, but in compliance with permit conditions. This was possibly due to an ammonia imbalance entering the catalyst, some flue gas bypassing the catalyst, or not enough catalyst volume. SO3 accounted for an average of 23% of the total sulfur oxides emissions measured. While some of the SO3 is formed in the combustion process, it is likely that the majority formed as the SO2 in the combustion products passed across the oxidizing CO catalyst and SCR catalyst.The 100 MW turbine sampled in this study emitted particle loadings of 3.63E-04 lb/MMBtu based on Methods 5.1/201A and 1.07E-04 lb/MMBtu based on SMPS method, which are similar to those previously measured from turbines in the SCAQMD area (FERCo et al., 2014), however, the turbine exhaust contained orders of magnitude higher particles than ambient air.
Keywords: Atmospheric nanoparticle; Method 201A; Method 5.1; Emission;
Impact of the New South Wales fires during October 2013 on regional air quality in eastern Australia by Géraldine Rea; Clare Paton-Walsh; Solène Turquety; Martin Cope; David Griffith (150-163).
Smoke plumes from fires contain atmospheric pollutants that can be transported to populated areas and effect regional air quality. In this paper, the characteristics and impact of the fire plumes from a major fire event that occurred in October 2013 (17–26) in the New South Wales (NSW) in Australia, near the populated areas of Sydney and Wollongong, are studied. Measurements from the Fourier Transform InfraRed (FTIR) spectrometer located at the University of Wollongong allowed a calculation of specific emission factors (EFs) in terms of grams per kilogram of dry fuel burned: 1640 g kg−1 of carbon dioxide; 107 g kg−1 of carbon monoxide; 7.8 g kg−1 of methane; and 0.16 g kg−1 of nitrous oxide. These EFs have then been used to calculate daily fire emissions for the NSW fire event using the APIFLAME emissions' model, leading to an increase of 54% of CO emitted compared to calculations with EFs from Akagi et al. (2011), widely used in the literature.Simulations have been conducted for this event using the regional chemistry-transport model (CTM) CHIMERE, allowing the first evaluation of its regional impact. Fire emissions are assumed well mixed into the boundary layer. The model simulations have been evaluated compared to measurements at the NSW air quality stations. The mean correlation coefficients (R) are 0.44 for PM10, 0.60 for PM2.5 and 0.79 for CO, with a negative bias for CO (−14%) and a positive bias for PM2.5 (64%). The model shows higher performance for lower boundary layer heights and wind speeds. According to the observations, 7 days show concentrations exceeding the air quality Australian national standards for PM10, 8 days for PM2.5. In the simulations, 5 days are correctly simulated for PM10, 8 days for PM2.5. For PM10, the model predicts 1 additional day of exceedance (one false detection). During this fire episode, inner Sydney is affected during 5 days by PM exceedances, that are mainly attributed to organic carbon in the model simulations.To evaluate the influence of the diurnal variability and the injection heights of fire emissions, two additional simulations were performed: one with all fire emissions injected below 1 km (CHIM_1 km), since satellite observations suggest low injection for this fire case, and one with a diurnal profile (CHIM_diu) adjusted to best match surface observations closest to the fires. CHIM_1 km displays less bias and root mean square error, and CHIM_diu presents a good agreement for hourly statistics for stations where peaks of PM are well captured, but enhances the differences when a peak is overestimated by the model. This sensitivity analysis highlights significant uncertainties related to these two key fire parameters (which add up to uncertainties on emissions), resulting in variations on concentrations of PM and CO.
Keywords: Air quality; Bushfires; Regional model; Sydney region; Injection height; Emissions; FTIR spectrometer; Emission factors;
Characteristics of NOx emission from Chinese coal-fired power plants equipped with new technologies by Zizhen Ma; Jianguo Deng; Zhen Li; Qing Li; Ping Zhao; Liguo Wang; Yezhu Sun; Hongxian Zheng; Li Pan; Shun Zhao; Jingkun Jiang; Shuxiao Wang; Lei Duan (164-170).
Coal combustion in coal-fired power plants is one of the important anthropogenic NOx sources, especially in China. Many policies and methods aiming at reducing pollutants, such as increasing installed capacity and installing air pollution control devices (APCDs), especially selective catalytic reduction (SCR) units, could alter NOx emission characteristics (NOx concentration, NO2/NOx ratio, and NOx emission factor). This study reported the NOx characteristics of eight new coal-fired power-generating units with different boiler patterns, installed capacities, operating loads, and coal types. The results showed that larger units produced less NOx, and anthracite combustion generated more NOx than bitumite and lignite combustion. During formation, the NOx emission factors varied from 1.81 to 6.14 g/kg, much lower than those of older units at similar scales. This implies that NOx emissions of current and future units could be overestimated if they are based on outdated emission factors. In addition, APCDs, especially SCR, greatly decreased NOx emissions, but increased NO2/NOx ratios. Regardless, the NO2/NOx ratios were lower than 5%, in accordance with the guidelines and supporting the current method for calculating NOx emissions from coal-fired power plants that ignore NO2.Display Omitted
Keywords: Coal-fired power plants; NO2/NOx ratio; NOx emission factor; Selective catalytic reduction (SCR);
Outdoor and indoor aerosol size, number, mass and compositional dynamics at an urban background site during warm season by N. Talbot; L. Kubelova; O. Makes; M. Cusack; J. Ondracek; P. Vodička; J. Schwarz; V. Zdimal (171-184).
This paper describes the use of a unique valve switching system that allowed for high temporal resolution indoor and outdoor data to be collected concurrently from online C-ToF-AMS, SMPS and OC/EC, and offline BLPI measurements. The results reveal near real-time dynamic aerosol behaviour along a migration path from an outdoor to indoor environment.An outdoor reduction in NR-PM1 mass concentration occurred daily from AM (06:00–12:00) to PM (12:00–18:00). SO4 (26%–37%) [AM/PM] increased proportionally during afternoons at the expense of NO3 (18%–7%). The influences of mixing height, temperature and solar radiation were considered against the mean mass concentration loss for each species. Losses were then calculated according to species via a basic input/output model. NO3 lost the most mass during afternoon periods, which we attribute to the accelerated dissociation of NH4NO3 through increasing temperature and decreasing relative humidity.Indoor/outdoor (I/O) ratios varied from 0.46 for <40 nm to 0.65 for >100 nm. These ratios were calculated using average SMPS PNC measurements over the full campaign and corroborated using a novel technique of calculating I/O penetration ratios through the indoor migration of particles during a new particle formation event. This ratio was then used to observe changes in indoor composition relative to those outdoors.Indoor sampling was carried out in an undisturbed room with no known sources. Indoor concentrations were found to be proportional to those outdoors, with organic matter [2.7 μg/m3] and SO4 [1.7 μg/m3] being the most prominent species. These results are indicative of fairly rapid aerosol penetration, a source-free indoor environment and small afternoon I/O temperature gradients. Fine fraction NO3 was observed indoors in both real-time AMS PM1 and off-line BLPI measurements. Greater mass concentration losses were observed from filter measurements, highlighting an important time dependency factor when investigating semi-volatiles. Coarse mode NO3 was observed by impactor measurements, ascribing value to observing the full particle mass size distribution for understanding aerosol origin.
Keywords: Aerosol; Composition; Dissociation; I/O ratio; Nitrate;
Emissions of hydrogen cyanide from on-road gasoline and diesel vehicles by Samar G. Moussa; Amy Leithead; Shao-Meng Li; Tak W. Chan; Jeremy J.B. Wentzell; Craig Stroud; Junhua Zhang; Patrick Lee; Gang Lu; Jeffery R. Brook; Katherine Hayden; Julie Narayan; John Liggio (185-195).
Hydrogen cyanide (HCN) is considered a marker for biomass burning emissions and is a component of vehicle exhaust. Despite its potential health impacts, vehicular HCN emissions estimates and their contribution to regional budgets are highly uncertain. In the current study, Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS) was used to measure HCN emission factors from the exhaust of individual diesel, biodiesel and gasoline vehicles. Laboratory emissions data as a function of fuel type and driving mode were combined with ambient measurement data and model predictions. The results indicate that gasoline vehicles have the highest emissions of HCN (relative to diesel fuel) and that biodiesel fuel has the potential to significantly reduce HCN emissions even at realistic 5% blend levels. The data further demonstrate that gasoline direct injection (GDI) engines emit more HCN than their port fuel injection (PFI) counterparts, suggesting that the expected full transition of vehicle fleets to GDI will increase HCN emissions. Ambient measurements of HCN in a traffic dominated area of Toronto, Canada were strongly correlated to vehicle emission markers and consistent with regional air quality model predictions of ambient air HCN, indicating that vehicle emissions of HCN are the dominant source of exposure in urban areas. The results further indicate that additional work is required to quantify HCN emissions from the modern vehicle fleet, particularly in light of continuously changing engine, fuel and after-treatment technologies.Laboratory and ambient measurements of hydrogen cyanide (HCN) from vehicles using high resolution Proton Transfer Reaction- Time of Flight- Mass Spectrometry (PTR-ToF-MS).Display Omitted
Keywords: Hydrogen cyanide; Biodiesel; Diesel; Gasoline; Emission factor; PFI; GDI; Biomass burning;
Aerosol optical properties and mixing state of black carbon in the Pearl River Delta, China by Haobo Tan; Li Liu; Shaojia Fan; Fei Li; Yan Yin; Mingfu Cai; P.W. Chan (196-208).
Aerosols contribute the largest uncertainty to the total radiative forcing estimate, and black carbon (BC) that absorbs solar radiation plays an important role in the Earth's energy budget. This study analysed the aerosol optical properties from 22 February to 18 March 2014 at the China Meteorological Administration Atmospheric Watch Network (CAWNET) station in the Pearl River Delta (PRD), China. The representative values of dry-state particle scattering coefficient (σsp), hemispheric backscattering coefficient (σhbsp), absorption coefficient (σabsp), extinction coefficient (σep), hemispheric backscattering fraction (HBF), single scattering albedo (SSA), as well as scattering Ångström exponent (α) were presented. A comparison between a polluted day and a clean day shows that the aerosol optical properties depend on particle number size distribution, weather conditions and evolution of the mixing layer. To investigate the mixing state of BC at the surface, an optical closure study of HBF between measurements and calculations based on a modified Mie model was employed for dry particles. The result shows that the mixing state of BC might be between the external mixture and the core-shell mixture. The average retrieved ratio of the externally mixed BC to the total BC mass concentration (rext-BC) was 0.58 ± 0.12, and the diurnal pattern of rext-BC can be found. Furthermore, considering that non-light-absorbing particles measured by a Volatility-Tandem Differential Mobility Analyser (V-TDMA) exist independently with core-shell and homogenously internally mixed BC particles, the calculated optical properties were just slightly different from those based on the assumption that BC exist in each particle. This would help understand the influence of the BC mixing state on aerosol optical properties and radiation budget in the PRD.
Keywords: Aerosol optical properties; Closure study; Mixing state of BC; PRD;
Climate change and pollutant emissions impacts on air quality in 2050 over Portugal by E. Sá; H. Martins; J. Ferreira; M. Marta-Almeida; A. Rocha; A. Carvalho; S. Freitas; C. Borrego (209-224).
Changes in climate and air pollutant emissions will affect future air quality from global to urban scale. In this study, regional air quality simulations for historical and future periods are conducted, with CAMx version 6.0, to investigate the impacts of future climate and anthropogenic emission projections on air quality over Portugal and the Porto metropolitan area in 2050. The climate and the emission projections were derived from the Representative Concentrations Pathways (RCP8.5) scenario. Modelling results show that climate change will impact NO2, PM10 and O3 concentrations over Portugal. The NO2 and PM10 annual means will increase in Portugal and in the Porto municipality, and the maximum 8-hr daily O3 value will increase in the Porto suburban areas (approximately 5%) and decrease in the urban area (approximately 2%). When considering climate change and projected anthropogenic emissions, the NO2 annual mean decreases (approximately 50%); PM10 annual mean will increase in Portugal and decrease in Porto municipality (approximately 13%); however PM10 and O3 levels increase and extremes occur more often, surpassing the currently legislated annual limits and displaying a higher frequency of daily exceedances. This air quality degradation is likely to be related with the trends found for the 2046–2065 climate, which implies warmer and dryer conditions, and with the increase of background concentrations of ozone and particulate matter. The results demonstrate the need for Portuguese authorities and policy-makers to design and implement air quality management strategies that take climate change impacts into account.
Keywords: Air quality; Atmospheric emissions; Climate change; Emission scenarios; Numerical modelling;
Simple, stable, and affordable: Towards long-term ecosystem scale flux measurements of VOCs by J. Rinne; T. Karl; A. Guenther (225-227).
Transport of tropospheric and stratospheric ozone over India: Balloon-borne observations and modeling analysis by P.R. Sinha; L.K. Sahu; R.K. Manchanda; V. Sheel; M. Deushi; M. Kajino; M.G. Schultz; N. Nagendra; P. Kumar; D.B. Trivedi; S.K. Koli; S.K. Peshin; Y.V. Swamy; C.G. Tzanis; S. Sreenivasan (228-242).
This study describes the spatio-temporal variation of vertical profiles of ozone (O3) measured by balloon-borne ozonesondes over two tropical sites of Trivandrum (TVM) and Hyderabad (HYD) in India from January 2009 to December 2010. In the lower troposphere, the mixing ratios of O3 over HYD (18–66 ppbv) were similar to TVM (18–65 ppbv). In the free troposphere, the O3 mixing ratios over HYD were higher than those over TVM throughout the year. In the tropical tropopause layer (TTL) region (above 15 km), the mixing ratios of O3 over TVM were higher (83–358 ppbv) compared to those measured over HYD (89–216 ppbv). Prevailing of O3 laminae between about 14 and 17 km is seen for both sites for most profiles. A strong seasonal variation of O3 is observed in the lower stratosphere between 18 and 24 km over TVM, however, it is not pronounced for HYD. Transport of air masses from the biomass burning region of the central Africa, Southeast Asia and the Indo Gangetic plains (IGP) influenced and led to enhancements of lower and mid-tropospheric O3 over HYD and TVM while, the isentropic (325 K) potential vorticity (PV) at 100 hPa showed transport of O3–rich air from the lower stratosphere to the upper troposphere during winter and spring months over both sites. The free tropospheric O3 mixing ratios (FT-O3; 0–4 km) contribute substantially to the tropospheric column O3 (TCO) with an annual average fraction of 30% and reveal the similar seasonal variations over HYD and TVM. The vertical profiles of O3 obtained from the Monitoring Atmospheric Composition and Climate - Interim Implementation (MACC-II) reanalysis and the Meteorological Research Institute-Chemistry Climate Model version 2 (MRI-CCM2) are compared with the ozonesonde data over both sites. The simulated magnitude, phase and vertical gradient of O3 from both MRI-CCM2 and MACC-II are in good agreement with measurements in the stratosphere while there are significant differences in the tropospheric columns.
Keywords: Ozonesone; Balloon-borne; ECC; India; Tropical;
Stable carbon and nitrogen isotopic compositions of ambient aerosols collected from Okinawa Island in the western North Pacific Rim, an outflow region of Asian dusts and pollutants by Bhagawati Kunwar; Kimitaka Kawamura; Chunmao Zhu (243-253).
Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios were measured for total carbon (TC) and nitrogen (TN), respectively, in aerosol (TSP) samples collected at Cape Hedo, Okinawa, an outflow region of Asian pollutants, during 2009–2010. The averaged δ13C and δ15N ratios are −22.2‰ and +12.5‰, respectively. The δ13C values are similar in both spring (−22.5‰) and winter (−22.5‰), suggesting the similar sources and/or source regions. We found that δ13C from Okinawa aerosols are ca. 2‰ higher than those reported from Chinese megacities probably due to photochemical aging of organic aerosols. A strong correlation (r = 0.81) was found between nss-Ca and TSP, suggesting that springtime aerosols are influenced from Asian dusts. However, carbonates in the Asian dusts were titrated with acidic species such as sulfuric acid and oxalic acid during atmospheric transport although two samples suggested the presence of remaining carbonate. No correlations were found between δ13C and tracer compounds (levoglucosan, elemental carbon, oxalic acid, and Na+). During winter and spring, coal burning is significant source in China. Based on isotopic mass balance, contribution of coal burning origin particles to total aerosol carbon was estimated as ca. 97% in winter, which is probably associated with the high emissions in China. Contribution of NO3 − to TN was on average 45% whereas that of NH4 + was 18%. These results suggest that vehicular exhaust is an important source of TN in Okinawa aerosols. Concentration of water-soluble organic nitrogen (WSON) is higher in summer, suggesting that WSON is more emitted from the ocean in warmer season whereas inorganic nitrogen is more emitted in winter and spring from pollution sources in the Asian continent.
Keywords: Isotope ratios; Total carbon; Total nitrogen; Nitrate; Water-soluble organic nitrogen;
Development of nitrogen dioxide and volatile organic compounds land use regression models to estimate air pollution exposure near an Italian airport by Alessandra Gaeta; Giorgio Cattani; Alessandro Di Menno di Bucchianico; Antonella De Santis; Giulia Cesaroni; Chiara Badaloni; Carla Ancona; Francesco Forastiere; Roberto Sozzi; Andrea Bolignano; Fabrizio Sacco (254-262).
The aim of this study was to evaluate the small scale spatial variability of nitrogen dioxide (NO2) and selected VOCs (benzene, toluene, acrolein and formaldehyde) concentrations using Land Use Regression models (LURs) in a complex multi sources domain (64 km2), containing a mid-size airport: the Ciampino Airport, located in Ciampino, Rome, Italy.46 diffusion tube samplers were deployed within a domain centred in the airport over two 2-weekly periods (June 2011–January 2012). GIS-derived predictor variables, with varying buffer size, were evaluated to model spatial variation of NO2, benzene, toluene, formaldehyde and acrolein annual average concentrations. The airport apportionment to air quality was investigated using a Lagrangian dispersion model (SPRAY). A stepwise selection procedure was used to develop the linear regression models. The models were validated using leave one out cross validation (LOOCV) method.In this study, the use of LURs was found to be effective to explain spatial variability of NO2 (adjusted-R2 = 0.72), benzene (adjusted-R2 = 0.53), toluene (adjusted-R2 = 0.50) and acrolein (adjusted-R2 = 0.51), while limited power was achieved with the formaldehyde modeling (adjusted-R2 = 0.24).For all pollutants LURs output showed that the small scale spatial variability was mainly explained by local traffic. The airport contribution to the observed spatial variability was adequately quantified only for acrolein (0.43 (±0.69) μg/m3 in an area of about 6 km2, SW located to the airport runway), while for NO2 and formaldehyde, only a little portion of the spatial variability in a limited portion of the study domain was attributable to airport related emissions.
Keywords: Land use regression; Spatial variation; Airport; NO2; Benzene; Toluene; Formaldehyde; Acrolein;
Influence of ozone and meteorological parameters on levels of polycyclic aromatic hydrocarbons in the air by Gordana Pehnec; Ivana Jakovljević; Anica Šišović; Ivan Bešlić; Vladimira Vađić (263-268).
Concentrations of ten polycyclic aromatic hydrocarbons (PAHs) in the PM10 particle fraction were measured together with ozone and meteorological parameters at an urban site (Zagreb, Croatia) over a one-year period. Data were subjected to regression analysis in order to determine the relationship between the measured pollutants and selected meteorological variables. All of the PAHs showed seasonal variations with high concentrations in winter and autumn and very low concentrations during summer and spring. All of the ten PAHs concentrations also correlated well with each other. A statistically significant negative correlation was found between the concentrations of PAHs and ozone concentrations and concentrations of PAHs and temperature, as well as a positive correlation between concentrations of PAHs and PM10 mass concentration and relative humidity. Multiple regression analysis showed that concentrations of PM10 and ozone, temperature, relative humidity and pressure accounted for 43–70% of PAHs variability. Concentrations of PM10 and temperature were significant variables for all of the measured PAH's concentrations in all seasons. Ozone concentrations were significant for only some of the PAHs, particularly 6-ring PAHs.
Keywords: Meteorology; Multiple linear regression; Ozone; PM10; Seasonal variations;
Laboratory testing of airborne brake wear particle emissions using a dynamometer system under urban city driving cycles by Hiroyuki Hagino; Motoaki Oyama; Sousuke Sasaki (269-278).
To measure driving-distance-based mass emission factors for airborne brake wear particulate matter (PM; i.e., brake wear particles) related to the non-asbestos organic friction of brake assembly materials (pads and lining), and to characterize the components of brake wear particles, a brake wear dynamometer with a constant-volume sampling system was developed. Only a limited number of studies have investigated brake emissions under urban city driving cycles that correspond to the tailpipe emission test (i.e., JC08 or JE05 mode of Japanese tailpipe emission test cycles). The tests were performed using two passenger cars and one middle-class truck. The observed airborne brake wear particle emissions ranged from 0.04 to 1.4 mg/km/vehicle for PM10 (particles up to 10 μm (in size), and from 0.04 to 1.2 mg/km/vehicle for PM2.5. The proportion of brake wear debris emitted as airborne brake wear particles was 2–21% of the mass of wear. Oxygenated carbonaceous components were included in the airborne PM but not in the original friction material, which indicates that changes in carbon composition occurred during the abrasion process. Furthermore, this study identified the key tracers of brake wear particles (e.g., Fe, Cu, Ba, and Sb) at emission levels comparable to traffic-related atmospheric environments.Display Omitted
Keywords: Brake wear debris; Brake abrasion dust; Oxygenated organic aerosol; Atmospheric antimony (Sb) emissions;
Gas-phase naphthalene concentration data recovery in ambient air and its relevance as a tracer of sources of volatile organic compounds by Iratxe Uria-Tellaetxe; Marino Navazo; Maite de Blas; Nieves Durana; Lucio Alonso; Jon Iza (279-288).
Despite the toxicity of naphthalene and the fact that it is a precursor of atmospheric photooxidants and secondary aerosol, studies on ambient gas-phase naphthalene are generally scarce. Moreover, as far as we are concerned, this is the first published one using long-term hourly ambient gas-phase naphthalene concentrations. In this work, it has been also demonstrated the usefulness of ambient gas-phase naphthalene to identify major sources of volatile organic compounds (VOC) in complex scenarios. Initially, in order to identify main benzene emission sources, hourly ambient measurements of 60 VOC were taken during a complete year together with meteorological data in an urban/industrial area. Later, due to the observed co-linearity of some of the emissions, a procedure was developed to recover naphthalene concentration data from recorded chromatograms to use it as a tracer of the combustion and distillation of petroleum products. The characteristic retention time of this compound was determined comparing previous GC-MS and GC-FID simultaneous analysis by means of relative retention times, and its concentration was calculated by using relative response factors. The obtained naphthalene concentrations correlated fairly well with ethene (r = 0.86) and benzene (r = 0.92). Besides, the analysis of daily time series showed that these compounds followed a similar pattern, very different from that of other VOC, with minimum concentrations at day-time. This, together with the results from the assessment of the meteorological dependence pointed out a coke oven as the major naphthalene and benzene emitting sources in the study area.
Keywords: Naphthalene; GC-FID/GC-MS; NMHC; VOC source apportionment; Air quality monitoring;
A dynamic urban air pollution population exposure assessment study using model and population density data derived by mobile phone traffic by Claudio Gariazzo; Armando Pelliccioni; Andrea Bolignano (289-300).
A dynamic city-wide air pollution exposure assessment study has been carried out for the urban population of Rome, Italy, by using time resolved population distribution maps, derived by mobile phone traffic data, and modelled air pollutants (NO2, O3 and PM2.5) concentrations obtained by an integrated air dispersion modelling system. More than a million of persons were tracked during two months (March and April 2015) for their position within the city and its surroundings areas, with a time resolution of 15 min and mapped over an irregular grid system with a minimum resolution of 0.26 × 0.34 Km2. In addition, demographics information (as gender and age ranges) were available in a separated dataset not connected with the total population one. Such BigData were matched in time and space with air pollution model results and then used to produce hourly and daily resolved cumulative population exposures during the studied period. A significant mobility of population was identified with higher population densities in downtown areas during daytime increasing of up to 1000 people/Km2 with respect to nigh-time one, likely produced by commuters, tourists and working age population. Strong variability (up to ±50% for NO2) of population exposures were detected as an effect of both mobility and time/spatial changing in pollutants concentrations. A comparison with the correspondent stationary approach based on National Census data, allows detecting the inability of latter in estimating the actual variability of population exposure. Significant underestimations of the amount of population exposed to daily PM2.5 WHO guideline was identified for the Census approach. Very small differences (up to a few μg/m3) on exposure were detected for gender and age ranges population classes.Display Omitted
Keywords: Dispersion model; Urban area; Human mobility; Particulate matter; Gaseous pollutants; Big data;
Fungal succession in relation to volatile organic compounds emissions from Scots pine and Norway spruce leaf litter-decomposing fungi by Valery Isidorov; Zofia Tyszkiewicz; Ewa Pirożnikow (301-306).
Leaf litter fungi are partly responsible for decomposition of dead material, nutrient mobilization and gas fluxes in forest ecosystems. It can be assumed that microbial destruction of dead plant materials is an important source of volatile organic compounds (VOCs) emitted into the atmosphere from terrestrial ecosystems. However, little information is available on both the composition of fungal VOCs and their producers whose community can be changed at different stages of litter decomposition. The fungal community succession was investigated in a litter bag experiment with Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) needle litter. The succession process can be divided into a several stages controlled mostly by changes in litter quality. At the very first stages of decomposition the needle litter was colonized by ascomycetes which can use readily available carbohydrates. At the later stages, the predominance of Trichoderma sp., the known producers of cellulolytic enzymes, was documented. To investigate the fungi-derived VOCs, eight fungi species were isolated. As a result of gas chromatographic analyses, as many as 75C2 ―C15 fungal volatile compounds were identified. Most components detected in emissions were very reactive substances: the principal groups of VOCs were formed by monoterpenes, carbonyl compounds and aliphatic alcohols. It was found that production of VOCs by fungi is species specific: only 10 metabolites were emitted into the gas phase by all eight species. The reported data confirm that the leave litter decomposition is important source of reactive organic compounds under the forest canopy.
Keywords: VOCs; Leave litter; Decomposition; Fungi;
A hybrid land use regression/AERMOD model for predicting intra-urban variation in PM2.5 by Drew R. Michanowicz; Jessie L.C. Shmool; Brett J. Tunno; Sheila Tripathy; Sara Gillooly; Ellen Kinnee; Jane E. Clougherty (307-315).
Characterizing near-source spatio-temporal variation is a long -standing challenge in air pollution epidemiology, and common intra-urban modeling approaches [e.g., land use regression (LUR)], do not account for short-term meteorological variation. Atmospheric dispersion modeling approaches, such as AERMOD, can account for near-source pollutant behavior by capturing source-meteorological interactions, but requires external validation and resolved background concentrations. In this study, we integrate AERMOD-based predictions for source-specific fine particle (PM2.5) concentrations into LUR models derived from total ambient PM2.5 measured at 36 unique sites selected to represent different source and elevation profiles, during summer and winter, 2012–2013 in Pittsburgh, Pennsylvania (PA). We modeled PM2.5 emissions from 207 local stationary sources in AERMOD, utilizing the monitoring locations as receptors, and hourly meteorological information matching each sampling period. Finally, we compare results of the integrated LUR/AERMOD hybrid model to those of the AERMOD + background and standard LUR models, at the full domain scale and within a 5 km2 sub-domain surrounding a large industrial facility. The hybrid model improved out-of-sample prediction accuracy by 2–10% over LUR alone, though performance differed by season, in part due to within-season temporal variability. We found differences up to 10 μg/m3 in predicted concentrations, and observed the largest differences within the industrial sub-domain. LUR underestimated concentrations from 500 to 2500 m downwind of major sources. The hybrid modeling approach we developed may help to improve intra-urban exposure estimates, particularly in regions of large industrial sources, sharp elevation gradients, or complex meteorology (e.g., frequent inversion events), such as Pittsburgh, PA. More broadly, the approach may inform the development of spatio-temporal modeling frameworks for air pollution exposure assessment for epidemiology.
Keywords: AERMOD; Meteorological dispersion; Exposure assessment; Land use regression; Near-source; PM2.5;
Region-dependent seasonal pattern of methane over Indian region as observed by SCIAMACHY by M. Kavitha; Prabha R. Nair (316-325).
The column averaged mixing ratio of methane (XCH4) from SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on-board satellite ENVISAT has been used to study its regional pattern and seasonal cycle over Indian region for the period 2003–2009. XCH4 varies from 1740 to 1890 ppbv over Indian region with distinct spatial and temporal features. The peak values are observed in monsoon and post monsoon and minimum in winter months, except over southern Peninsular India which shows the distinctly different seasonal behavior with peak in October/November. The mean background level of XCH4 over Indian region is estimated as ∼1795 ppbv. While regional patterns are strongly associated with livestock distribution, wetland emissions, including rice fields, the seasonal variations in XCH4 are predominantly associated with the rice cultivation as revealed by analysis of NDVI.
Keywords: Methane; SCIAMACHY; Seasonal variation; Source analysis; Regional variation;
On-line algorithm for ground-level ozone prediction with a mobile station by Juš Kocijan; Dejan Gradišar; Marija Zlata Božnar; Boštjan Grašič; Primož Mlakar (326-333).
It is important to be able to predict high concentrations of tropospheric ozone and to inform the population about any violations of air-quality standards, as defined by international regulations. Although first-principle models that cover large geographical regions and different atmospheric layers are improving constantly, they typically still only cover geographical regions with a relatively low resolution. Such model predictions can be problematic for the micro-locations of a complex terrain, i.e., a terrain with a large geographical diversity or urban terrain. For such micro-locations, statistical models can be utilised. This paper presents a modelling and prediction algorithm that can be used in, or in accordance with, a mobile air-quality measurement station. Such a mobile station would enable the set-up of a statistical model and a relatively rapid access to the model's predictions for a specific geographical micro-location without a large quantity of historical of measurements. Uncertainty information about the model's predictions is also usually required. In addition, such a model can adapt to long-term changes, such as climate changes. In the paper we propose Gaussian-process models for the described modelling and prediction. In particular, we selected evolving Gaussian-process models that update on-line with the incoming measurement data. The proposed algorithm for the mobile air-quality measurement and the forecasting station is evaluated on measurements from five locations in Slovenia with different topographical and geographical properties. The obtained evaluation results confirm the feasibility of the concept.
Keywords: Air pollution; Ozone; Prediction of ozone concentration; Mobile air-quality measurement station; Statistical modelling; Gaussian-process model; Evolving model;
Effects of water and CMA in mitigating industrial road dust resuspension by Fulvio Amato; Alberto Escrig; Vicenta Sanfelix; Irina Celades; Cristina Reche; Eliseo Monfort; Xavier Querol (334-340).
Water spraying and/or chemical suppressants such as salts and polymers have been suggested to reduce road dust resuspension due to their capability to increase adhesion, and therefore the effective size and weight of particles, but contrasting results have been obtained so further testing are needed. This study presents the first results of street washing and Calcium Magnesium Acetate (CMA) efficiencies at two industrial roads (paved and unpaved) in the Mediterranean region where the high solar radiation, warm climate, and scarce precipitation, may play a key role in determining the efficiency of mitigation techniques Results show that, at both sites, street washing (water only) was more effective than CMA. Street washing made observe 18% (daily basis) and >90% (first hour) reductions of kerbside PM10 concentrations for the paved and unpaved road respectively, while with CMA PM10 decrease was generally lower and with less statistical significance.
Keywords: PM10; Road dust; Soil; Mineral; Crustal; CMA;
Urban scale air quality modelling using detailed traffic emissions estimates by C. Borrego; J.H. Amorim; O. Tchepel; D. Dias; S. Rafael; E. Sá; C. Pimentel; T. Fontes; P. Fernandes; S.R. Pereira; J.M. Bandeira; M.C. Coelho (341-351).
The atmospheric dispersion of NOx and PM10 was simulated with a second generation Gaussian model over a medium-size south-European city. Microscopic traffic models calibrated with GPS data were used to derive typical driving cycles for each road link, while instantaneous emissions were estimated applying a combined Vehicle Specific Power/Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (VSP/EMEP) methodology. Site-specific background concentrations were estimated using time series analysis and a low-pass filter applied to local observations. Air quality modelling results are compared against measurements at two locations for a 1 week period. 78% of the results are within a factor of two of the observations for 1-h average concentrations, increasing to 94% for daily averages. Correlation significantly improves when background is added, with an average of 0.89 for the 24 h record. The results highlight the potential of detailed traffic and instantaneous exhaust emissions estimates, together with filtered urban background, to provide accurate input data to Gaussian models applied at the urban scale.
Keywords: Urban air quality; Gaussian model; Traffic modelling; Emissions modelling; Monitoring campaign; Background concentration;
Biomonitoring potential of five sympatric Tillandsia species for evaluating urban metal pollution (Cd, Hg and Pb) by Alejandro Sánchez-Chardi (352-359).
The present study quantifies non essential heavy metals highly toxic for biological systems (Pb, Hg and Cd) in five autochthonous epiphytic plants from Tillandsia genus (T. recurvata, T. meridionalis, T. duratii, T. tricholepis, T. loliacea) according to different traffic levels (reference, low, medium and high polluted sites) in Asunción (Paraguay). The three metals increased in polluted sites following Pb (till 62.99 ppm in T. tricholepis) > Cd (till 1.35 ppm in T. recurvata) > Hg (till 0.36 ppm in T. recurvata) and Pb and Cd levels were directly related to traffic flow. Although the species showed similar bioaccumulation pattern (namely, higher levels of metals in polluted sites), enrichment factors (maximum EF values 37.00, 18.16, and 11.90 for Pb, Hg, and Cd, respectively) reported T. tricholepis as the most relevant bioindicator due to its wide distribution and abundance in study sites, low metal content in control site and high metal contents in polluted sites, and significant correlations with traffic density of Pb and Cd. This study emphasizes the necessity of biomonitoring air pollution in areas out of air monitoring control such as Asunción, where the high levels of metal pollution especially Pb, may represent an increment of risk for the human population inhabiting this urban area.Display Omitted
Keywords: Urban pollution; Tillandsia; Heavy metal; Biomonitoring; Paraguay;
Speciated atmospheric mercury in the marine boundary layer of the Bohai Sea and Yellow Sea by Chunjie Wang; Zhijia Ci; Zhangwei Wang; Xiaoshan Zhang; Jia Guo (360-370).
The objectives of this study are to identify the spatial and temporal distributions of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and fine particulate mercury (HgP 2.5) in the marine boundary layer (MBL) of the Bohai Sea (BS) and Yellow Sea (YS), and to investigate the relationships between mercury species and meteorological parameters. The mean concentrations of GEM, RGM, and HgP 2.5 were 2.03 ng m−3, 2.5 pg m−3, and 8.2 pg m−3 in spring, and 2.09 ng m−3, 4.3 pg m−3, and 8.3 pg m−3 in fall. Reactive mercury (RGM + HgP 2.5) represented < 1% of total atmospheric mercury (GEM + RGM + HgP 2.5), which indicated that most mercury export in the MBL was GEM and the direct outflow of reactive mercury was very small. Moreover, GEM concentrations over the BS were generally higher than those over the YS both in spring and fall. Although RGM showed a homogeneous distribution over the BS and YS both in spring and fall, the mean RGM concentration in fall was significantly higher than that in spring. In contrast, the spatial distribution of HgP 2.5 generally reflected a gradient with high levels near the coast of China and low levels in the open sea, suggesting the significant atmospheric mercury outflow from China. Interestingly, the mean RGM concentrations during daytime were significantly higher than those during nighttime both in spring and fall, while the opposite results were observed for HgP 2.5. Additionally, RGM positively correlates with air temperature while negatively correlates with relative humidity. In conclusion, the elevated atmospheric mercury levels in the BS and YS compared to other open seas suggested that the human activities had a significant influence on the oceanic mercury cycle downwind of China.
Keywords: Gaseous elemental mercury; Reactive gaseous mercury; Fine particulate mercury; Marine boundary layer;
Constraining NOx emissions using satellite NO2 measurements during 2013 DISCOVER-AQ Texas campaign by Amir Hossein Souri; Yunsoo Choi; Wonbae Jeon; Xiangshang Li; Shuai Pan; Lijun Diao; David A. Westenbarger (371-381).
Reliable emission inventories are key to precisely model air pollutant concentrations. The relatively large reduction in NOx emissions that is well corroborated by satellite and in-situ observations over southeast Texas has resulted in discrepancies between observations and regional model simulations based on the National Emission Inventory (NEI) provided every three years in U.S. In this study, a Bayesian inversion of OMI tropospheric NO2 is conducted to update anthropogenic sources of NEI-2011 and soil-biogenic sources from BEIS3 (Biogenic Emission Inventory System version 3) over southeast Texas and west Louisiana during the 2013 DISCOVER-AQ Texas campaign. Results reveal that influences of the a priori profile used in OMI NO2 retrieval play a significant role in inconsistencies between model and satellite observations, which should be mitigated. A posteriori emissions are produced using the regional Community Multiscale Air Quality (CMAQ) model associated with Decoupled Direct Method (DDM) sensitivity analysis. The inverse estimate suggests a reduction in area (44%), mobile (30%), and point sources (60%) in high NOx areas (ENOx> 0.2 mol/s), and an increase in soil (∼52%) and area emissions (37%) in low NOx regions (ENOx< 0.02 mol/s). The reductions in anthropogenic sources in high NOx regions are attributed to both uncertainty of the priori and emissions policies, while increases in area and soil-biogenic emissions more likely resulted from under-estimation of ships emissions, and the Yienger- Levy scheme used in BEIS respectively. In order to validate the accuracy of updated NOx emissions, CMAQ simulation was performed and results were evaluated with independent surface NO2 measurements. Comparing to surface monitoring sites, we find improvements (before and after inverse modeling) for MB (1.95, −0.30 ppbv), MAB (3.65, 2.60 ppbv), RMSE (6.13, 4.37 ppbv), correlation (0.68, 0.69), and IOA (0.76, 0.82). The largest improvement is seen for morning time surface NO2 for which RMSE and MB are reduced considerably by ∼60% (5.05 to 2.07 ppbv) and 109% (3.49 to −0.3 ppbv). However, under-prediction of model NO2 in Houston on 09/25–09/26 likely resulting from unprecedented local NOx sources from the Houston Ship Channel (HSC) becomes more evident. Overall, results show that use of OMI tropospheric NO2 columns can substantially reduce the uncertainty of bottom-up emissions for a regional study which should be extended to larger domains (e.g. entire U.S. or North America).
Keywords: NOx emissions; Data assimilation; Bayesian; CMAQ DDM; Remote sensing;
Oxidative potential of secondary organic aerosols produced from photooxidation of different hydrocarbons using outdoor chamber under ambient sunlight by Huanhuan Jiang; Myoseon Jang; Tara Sabo-Attwood; Sarah E. Robinson (382-389).
The oxidative potential of various secondary organic aerosols (SOA) was measured using dithiothreitol (DTT) assay to understand how organic aerosols react with cellular materials. SOA was produced via the photooxidation of four different hydrocarbons (toluene, 1,3,5-trimethylbenzene, isoprene and α-pinene) in the presence of NOx using a large outdoor photochemical smog chamber. The DTT consumption rate was normalized by the aerosol mass, which is expressed as DTT mass . Toluene SOA and isoprene SOA yielded higher DTT mass than 1,3,5-trimethylbenzene SOA or α-pinene SOA. In order to discover the correlation between the molecular structure and oxidative potential, the DTT responses of selected model compounds were also measured. Among them, conjugated aldehydes, quinones, and H2O2 showed considerable DTT response. To investigate the correlation between DTT response and cell responses in vitro, the expression of biological markers, i.e. IL-6, IL-8, and HMOX-1 were studied using small airway epithelial cells. Higher cellular expression of IL-8 was observed with toluene SOA exposure compared to 1,3,5-trimethylbenzene SOA exposure, which aligned with the results from DTT assay. Our study also suggests that within the urban atmosphere, the contribution of toluene SOA and isoprene SOA to the oxidative potential of ambient SOA will be more significant than that of α-pinene SOA.
Keywords: Oxidative potential; Secondary organic aerosols; DTT assay; Cell response; Human small airway epithelial cells;
A hybrid prediction model for PM2.5 mass and components using a chemical transport model and land use regression by Qian Di; Petros Koutrakis; Joel Schwartz (390-399).
GEOS-Chem, a chemical transport model, provides time-space continuous estimates of atmospheric pollutants including PM2.5 and its major components, but model predictions are not highly correlated with ground monitoring data. In addition, its spatial resolution is usually too coarse to characterize the spatial pattern in pollutant concentrations in urban environments. Our objective was to calibrate daily GEOS-Chem simulations using ground monitoring data and incorporating meteorological variables, land-use terms and spatial-temporal lagged terms. Major PM2.5 components of our interest include sulfate, nitrate, organic carbon, elemental carbon, ammonium, sea salt and dust. We used a backward propagation neural network to calibrate GEOS-Chem predictions with a spatial resolution of 0.500° × 0.667° using monitoring data collected during the period from 2001 to 2010 for the Northeastern United States. Subsequently, we made predictions at 1 km × 1 km grid cells. We determined the accuracy of the spatial-temporal predictions using ten-fold cross-validation and “leave-one-day-out” cross-validation techniques. We found a high total R2 for PM2.5 mass (all data R2 0.85, yearly values: 0.80–0.88) and PM2.5 components (R2 for individual components were around 0.70–0.80). Our model makes it possible to assess spatially- and temporally-resolved short- and long-term exposures to PM2.5 mass and components for epidemiological studies.
Keywords: PM2.5; PM2.5 components; Neural network; Chemical transport model; Land use regression; Epidemiology;
Characteristics of atmospheric particulate mercury in size-fractionated particles during haze days in Shanghai by Xiaojia Chen; Rajasekhar Balasubramanian; Qiongyu Zhu; Sailesh N. Behera; Dandan Bo; Xian Huang; Haiyun Xie; Jinping Cheng (400-408).
Atmospheric particulate mercury (PHg) is recognized as a global pollutant that requires regulation because of its significant impacts on both human health and wildlife. The haze episodes that occur frequently in China could influence the transport and fate of PHg. To examine the characteristics of PHg during haze and non-haze days, size-fractioned particles were collected using thirteen-stage Nano-MOUDI samplers (10 nm–18 μm) during a severe haze episode (from December 2013 to January 2014) in Shanghai. The PHg concentration on haze days (4.11 ± 0.53 ng m−3) was three times higher than on non-haze days (1.34 ± 0.15 ng m−3). The ratio of the PHg concentration to total gaseous mercury (TGM) ranged from 0.42 during haze days to 0.21 during non-haze days, which was possibly due to the elevated concentration of particles for gaseous elemental mercury (GEM) adsorption, elevated sulfate and nitrate contributing to GEM oxidation, and the catalytic effect of elevated water-soluble inorganic metal ions. PHg/PM10 during haze days (0.019 ± 0.004 ng/μg) was lower than during non-haze days (0.024 ± 0.002 ng/μg), and PHg/PM10 was significantly reduced with an increasing concentration of PM10, which implied a relatively lower growth velocity of mercury than other compositions on particles during haze days, especially in the diameter range of 0.018–0.032 μm.During haze days, each size-fractioned PHg concentration was higher than the corresponding fraction on non-haze days, and the dominant particle size was in the accumulation mode, with constant accumulation to a particle size of 0.56–1.0 μm. The mass size distribution of PHg was bimodal with peaks at 0.32–0.56 μm and 3.1–6.2 μm on non-haze days, and 0.56–1.0 μm and 3.1–6.2 μm on haze days. There was a clear trend that the dominant size for PHg in the fine modes shifted from 0.32–0.56 μm during non-haze days to 0.56–1.0 μm on haze days, which revealed the higher growth velocity of PHg on haze days due to the condensation and accumulation of Hg in particles. Traffic emissions and coal combustion may contribute to the high concentrations of Hg, because PHg of every size was found to correlate positively with SO2, NO2, and CO. A correlation was found between every mode of PHg and relative humidity, which affected the gas-particle partitioning of semi-volatile organic compounds, resulting in effective partitioning into aerosols. The strong correlations between Hg and water-soluble ions implied the oxidation of elemental Hg was the main gas-to-particle chemical transformation process.
Keywords: Atmospheric particulate mercury; Size-fractionated; Growth characteristics; Transformation pathway; Haze days;
Assessment of factors influencing PM mass concentration measured by gravimetric & beta attenuation techniques at a suburban site by E. Triantafyllou; E. Diapouli; E.M. Tsilibari; A.D. Adamopoulos; G. Biskos; K. Eleftheriadis (409-417).
Near real-time atmospheric particulate matter (PM) monitors are extensively used in air quality networks given their ability to provide continuous measurements with minimal attention by the operator. Their principle of operation is based on measurement of a physical parameter that is quantitatively linked to the PM mass concentration. Significant discrepancies between these measurements and those obtained by the reference gravimetric method, conducted in regions with diverse climatic conditions, have been reported in the literature. In this study we compare systematic PM2.5 and PM10 gravimetric (GM) and beta attenuation (BA) measurements performed at a suburban site in Athens, Greece, over a period of 4 years (2009–2012). In general, BA and GM datasets exhibited similar temporal variation for both PM size fractions. An overestimation of the ΒΑ measurements, which was ∼30% for the PM2.5 and ∼10% for the PM10 data, was observed. Good linear correlations between GM and BA data were observed, with estimated Pearson coefficients being 0.79 for the PM2.5 and 0.85 for the PM10 measurements. The respective fitted equations through the entire dataset were BA = 0.71 GM + 6.2, and BA = 0.77 G M + 4.1. Better correlation between GM and BA measurements was observed during the cold rather than the warm period. Discrepancies between BA and GM PM2.5 measurements increased with increasing available water vapor, suggesting that the aerosol bound water has a strong effect on the measurements. The effect of filter material used for GM measurements (i.e., quartz, glass fiber, or Teflon) was also examined for the PM2.5 dataset. Best correlation between BA and GM data was observed when glass fiber, which is incidentally the material of the BA filter tape, was used in the GM measurements. When the BA to GM relationship was examined by further categorizing the data by the season (i.e., cold and warm period) for different filter types, the relationships that were fitted to the data for the two seasons were similar when Teflon filters were used, but quite diverse when quartz and glass fiber filters were employed in the GM measurements. Finally, the variability of the ratio between the two measurement techniques was found to be potentially dependent on the availability of the volatility or stability in the aerosol phase of species such as ammonium nitrate.
Keywords: PM2.5, PM10; Beta-attenuation monitor; Reference gravimetric sampler; Water content; Filter material; Equivalence;
Modeling of atmospheric OH reaction rates using newly developed variable distance weighted zero order connectivity index by Jernej Markelj; Matevž Pompe (418-423).
A new variable distance weighted zero order connectivity index was used for development of structure-activity relationship for modeling reactivity of OH radical with alkanes and non-conjugated alkenes in the atmosphere. The proposed model is based on the assumptions that the total reaction rate can be obtained by summing all partial reaction rates and that all reaction sites are interrelated by influencing each other. The results suggest that these assumptions are justified. The model was compared with the EPA implemented model in the studied application domain and showed superior prediction capabilities. Further, optimized values of the weights that were used in our model permit some insight into mechanisms that govern the reaction OH + alkane/alkene. The most important conclusion is that the branching degree of the forming radical seems to play a major role in site specific reaction rates. Relative qualitative structural interpretation is possible, e.g. allylic site is suggested to be much more reactive than even tertiary sp3 carbon.Novel modeling software MACI, which was developed in our lab and is now available for research purposes, was used for calculations. Various variable topological indices that are again starting to be recognized because of their great potentials in simplicity, fast calculations, very good correlations and structural information, were implemented in the program.Display Omitted
Keywords: Modeling; OH reactivity; Partial reaction rate; Variable connectivity index; QSAR; MACI;
SOA formation from naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene photooxidation by Chia-Li Chen; Mary Kacarab; Ping Tang; David R. Cocker (424-433).
The SOA yield and chemical characteristics of SOA formation from naphthalene and two methyl substituted naphthalenes, 1-methylnaphthalene and 2-methylnaphthalene, were studied for high NOx, low NOx, and ultra-low NOx conditions. The SOA yields are high compared to previous studies for all three PAHs precursors: 1-methylnaphthalene > 2-methylnaphthalene ∼ naphthalene for all atmospheric conditions studied. The SOA yields range from 0.03 to 0.60 for naphthalene, 0.21–1.52 for 1-methylnaphthalene, and 0.34–0.55 for 2-methylnaphthalene under high NOx with HONO (initial PAH:NO ratio = 0.03–0.17) conditions. The SOA yield ranges from 0.04 to 0.31 for naphthalene, 0.14–0.72 for 1-methylnaphthalene, and 0.06–0.49 for 2-methylnaphthalene under low NOx (initial PAH:NO ratio = 0.54–2.20) conditions. SOA yields were substantially greater than 1.0 under H2O2 (ultra low NOx) and low NOx + H2O2 conditions for all three PAH precursors. The system reactivity influenced by OH radicals, NOx levels, initial PAH/NO ratios, NO2/NO ratios, and all impacted the SOA formation from the PAH precursors. Fractal-like SOA is observed for the methylnaphthalene isomers during high NOx photooxidation experiments, implying that researchers studying SOA formation from this precursor must carefully account for particle shape or effective density. A m/z 104 (C7H4O+,104.026) peak, consistent with SOA products phthalic acid from earlier studies, was observed as a potential marker of PAH oxidation during HR-ToF-AMS analysis.
Keywords: SOA yield; m/z 104; Naphthalene; Methylnaphthalene; PAH; Fractal agglomerate;