Atmospheric Environment (v.164, #C)
Editorial board (i).
Technical note: Aerosol light absorption measurements with a carbon analyser – Calibration and precision estimates by B.A.J. Ammerlaan; R. Holzinger; A.D. Jedynska; J.S. Henzing (1-7).
Equivalent Black Carbon (EBC) and Elemental Carbon (EC) are different mass metrics to quantify the amount of combustion aerosol. Both metrics have their own measurement technique. In state-of-the-art carbon analysers, optical measurements are used to correct for organic carbon that is not evolving because of pyrolysis. These optical measurements are sometimes used to apply the technique of absorption photometers. Here, we use the transmission measurements of our carbon analyser for simultaneous determination of the elemental carbon concentration and the absorption coefficient. We use MAAP data from the CESAR observatory, the Netherlands, to correct for aerosol-filter interactions by linking the attenuation coefficient from the carbon analyser to the absorption coefficient measured by the MAAP. Application of the calibration to an independent data set of MAAP and OC/EC observations for the same location shows that the calibration is applicable to other observation periods. Because of simultaneous measurements of light absorption properties of the aerosol and elemental carbon, variation in the mass absorption efficiency (MAE) can be studied. We further show that the absorption coefficients and MAE in this set-up are determined within a precision of 10% and 12%, respectively. The precisions could be improved to 4% and 8% when the light transmission signal in the carbon analyser is very stable.
Keywords: Black carbon; Elemental carbon; Aerosol light absorption; Mass absorption efficiency;
Source apportionment of biogenic contributions to ozone formation over the United States by Rui Zhang; Alexander Cohan; Arastoo Pour Biazar; Daniel S. Cohan (8-19).
Vegetation is the leading emitter of volatile organic compounds (VOC), a key ingredient for ozone formation. The contribution of biogenic VOC (BVOC) emissions to regional ozone formation needs better quantification so that air quality regulators can effectively design emission control strategies. One of the key uncertainties for modeling BVOC emissions comes from the estimation of photosynthetically active radiation (PAR) reaching canopy. Satellite insolation retrieval data provide an alternative to prognostic meteorological models for representing the spatial and temporal variations of PAR. In this study, biogenic emission estimates generated with the MEGAN and BEIS biogenic emissions models using satellite or prognostic PAR are used to examine the contribution of BVOC to ozone in the United States. The Comprehensive Air Quality Model with Extensions (CAMx) is applied with Ozone Source Apportionment Technology (OSAT) and brute force zero-out sensitivity runs to quantify the biogenic contributions to ozone formation during May through September 2011. The satellite PAR retrievals are on average lower than modeled PAR and exhibit better agreement with SCAN and SURFRAD network measurements. Using satellite retrievals instead of modeled PAR reduces BEIS and MEGAN estimates of isoprene by an average of 3%–4% and 9%–12%, respectively. The simulations still overestimate observed ground-level isoprene concentrations by a factor of 1.1 for BEIS and 2.6 for MEGAN. The spatial pattern of biogenic ozone contribution diagnosed from OSAT differs from the brute force zero-out sensitivity results, with the former more smoothly distributed and the latter exhibiting peak impacts near metropolitan regions with intense anthropogenic NOx emissions. OSAT tends to apportion less ozone to biogenics as BVOC emissions increase, since that shifts marginal ozone formation toward more NOx-limited conditions. By contrast, zero-out source apportionment of ozone to biogenics increases with BVOC emissions. OSAT simulations with BEIS show that BVOCs typically contribute 10–19% to regional ozone concentrations at nonattainment receptor sites during episode days.
Keywords: Biogenic emissions; Photosynthetically active radiation (PAR); Ozone Source Apportionment Technology (OSAT); CAMx; Ozone; Geostationary Operational Environmental Satellite (GOES);
Impact of chemical plant start-up emissions on ambient ozone concentration by Sijie Ge; Sujing Wang; Qiang Xu; Thomas Ho (20-30).
Flare emissions, especially start-up flare emissions, during chemical plant operations generate large amounts of ozone precursors that may cause highly localized and transient ground-level ozone increment. Such an adverse ozone impact could be aggravated by the synergies of multiple plant start-ups in an industrial zone. In this paper, a systematic study on ozone increment superposition due to chemical plant start-up emissions has been performed. It employs dynamic flaring profiles of two olefin plants’ start-ups to investigate the superposition of the regional 1-hr ozone increment. It also summaries the superposition trend by manipulating the starting time (00:00–10:00) of plant start-up operations and the plant distance (4–32 km). The study indicates that the ozone increment induced by simultaneous start-up emissions from multiple chemical plants generally does not follow the linear superposition of the ozone increment induced by individual plant start-ups. Meanwhile, the trend of such nonlinear superposition related to the temporal (starting time and operating hours of plant start-ups) and spatial (plant distance) factors is also disclosed. This paper couples dynamic simulations of chemical plant start-up operations with air-quality modeling and statistical methods to examine the regional ozone impact. It could be helpful for technical decision support for cost-effective air-quality and industrial flare emission controls.Display Omitted
Keywords: Ozone pollution; Ozone increment superposition; Plant start-ups; Air-quality modeling;
Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates by Elena Garcia-Anton; Soledad Cuezva; Angel Fernandez-Cortes; Miriam Alvarez-Gallego; Concepcion Pla; David Benavente; Juan Carlos Cañaveras; Sergio Sanchez-Moral (31-49).
This study characterizes the processes involved in seasonal CO2 exchange between soils and shallow underground systems and explores the contribution of the different biotic and abiotic sources as a function of changing weather conditions. We spatially and temporally investigated five karstic caves across the Iberian Peninsula, which presented different microclimatic, geologic and geomorphologic features. The locations present Mediterranean and Oceanic climates. Spot air sampling of CO2 (g) and δ13CO2 in the caves, soils and outside atmospheric air was periodically conducted. The isotopic ratio of the source contribution enhancing the CO2 concentration was calculated using the Keeling model. We compared the isotopic ratio of the source in the soil (δ13Cs–soil) with that in the soil-underground system (δ13Cs–system). Although the studied field sites have different features, we found common seasonal trends in their values, which suggests a climatic control over the soil air CO2 and the δ13CO2 of the sources of CO2 in the soil (δ13Cs–soil) and the system (δ13Cs–system). The roots respiration and soil organic matter degradation are the main source of CO2 in underground environments, and the inlet of the gas is mainly driven by diffusion and advection. Drier and warmer conditions enhance soil-exterior CO2 interchange, reducing the CO2 concentration and increasing the δ13CO2 of the soil air. Moreover, the isotopic ratio of the source of CO2 in both the soil and the system tends to heavier values throughout the dry and warm season.We conclude that seasonal variations of soil CO2 concentration and its 13C/12C isotopic ratio are mainly regulated by thermo-hygrometric conditions. In cold and wet seasons, the increase of soil moisture reduces soil diffusivity and allows the storage of CO2 in the subsoil. During dry and warm seasons, the evaporation of soil water favours diffusive and advective transport of soil-derived CO2 to the atmosphere. The soil CO2 diffusion is enough important during this season to modify the isotopic ratio of soil produced CO2 (3–6‰ heavier). Drought induces release of CO2 with an isotopic ratio heavier than produced by organic sources. Consequently, climatic conditions drive abiotic processes that turn regulate a seasonal storage of soil-produced CO2 within soil and underground systems. The results here obtained imply that abiotic emissions of soil-produced CO2 must be an inherent consequence of droughts, which intensification has been forecasted at global scale in the next 100 years.
Keywords: Vadose zone; CO2 exchange; δ13CO2; Climatic control; Soil CO2 diffusion;
Modeling emission rates and exposures from outdoor cooking by Rufus Edwards; Marko Princevac; Robert Weltman; Masoud Ghasemian; Narendra K. Arora; Tami Bond (50-60).
Approximately 3 billion individuals rely on solid fuels for cooking globally. For a large portion of these – an estimated 533 million – cooking is outdoors, where emissions from cookstoves pose a health risk to both cooks and other household and village members. Models that estimate emissions rates from stoves in indoor environments that would meet WHO air quality guidelines (AQG), explicitly don't account for outdoor cooking. The objectives of this paper are to link health based exposure guidelines with emissions from outdoor cookstoves, using a Monte Carlo simulation of cooking times from Haryana India coupled with inverse Gaussian dispersion models. Mean emission rates for outdoor cooking that would result in incremental increases in personal exposure equivalent to the WHO AQG during a 24-h period were 126 ± 13 mg/min for cooking while squatting and 99 ± 10 mg/min while standing. Emission rates modeled for outdoor cooking are substantially higher than emission rates for indoor cooking to meet AQG, because the models estimate impact of emissions on personal exposure concentrations rather than microenvironment concentrations, and because the smoke disperses more readily outdoors compared to indoor environments. As a result, many more stoves including the best performing solid-fuel biomass stoves would meet AQG when cooking outdoors, but may also result in substantial localized neighborhood pollution depending on housing density. Inclusion of the neighborhood impact of pollution should be addressed more formally both in guidelines on emissions rates from stoves that would be protective of health, and also in wider health impact evaluation efforts and burden of disease estimates. Emissions guidelines should better represent the different contexts in which stoves are being used, especially because in these contexts the best performing solid fuel stoves have the potential to provide significant benefits.
Keywords: Cookstoves; Exposures; Air quality guidelines; Emissions rates; ISO standards;
The OH-initiated oxidation of atmospheric peroxyacetic acid: Experimental and model studies by Huihui Wu; Yin Wang; Huan Li; Liubin Huang; Dao Huang; Hengqing Shen; Yanan Xing; Zhongming Chen (61-70).
Peroxyacetic acid (PAA, CH3C(O)OOH) plays an important role in atmospheric chemistry, serving as reactive oxidant and affecting radical recycling. However, previous studies revealed an obvious gap between modelled and observed concentrations of atmospheric PAA, which may be partly ascribed to the uncertainty in the kinetics and mechanism of OH-oxidation. In this study, we measured the rate constant of OH radical reaction with PAA (k PAA+OH) and investigated the products in order to develop a more robust atmospheric PAA chemistry. Using the relative rates technique and employing toluene and meta-xylene as reference compounds, the k PAA+OH was determined to be (9.4–11.9) × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm, which is about (2.5–3.2) times larger than that parameter used in Master Chemical Mechanism v3.3.1 (MCM v3.3.1) (3.70 × 10−12 cm3 molecule−1 s−1). Incorporation of a box model and MCM v3.3.1 with revised PAA chemistry represented a better simulation of atmospheric PAA observed during Wangdu Campaign 2014, a rural site in North China Plain. It is found that OH-oxidation is an important sink of atmospheric PAA in this rural area, accounting for ∼30% of the total loss. Moreover, the major terminal products of PAA–OH reaction were identified as formaldehyde (HCHO) and formic acid (HC(O)OH). The modelled results show that both primary and secondary chemistry play an important role in the large HCHO and HC(O)OH formation under experimental conditions. There should exist the channel of methyl H-abstraction for PAA–OH reaction, which may also provide routes to HCHO and HC(O)OH formation.
Keywords: Peroxyacetic acid; OH-oxidation; Rate constant; Reaction channel; Sink;
Influence of NH3 on secondary organic aerosols from the ozonolysis and photooxidation of α-pinene in a flow reactor by Zaeem Bin Babar; Jun-Hyun Park; Ho-Jin Lim (71-84).
This study presents detailed characterizations of a newly-developed flow reactor including (1) residence time distribution measurements, (2) relative humidity (RH) and temperature control, and (3) OH radical exposure range (i.e., atmospheric aging time). Hydroxyl (OH) radical exposures ranged from 8.20 × 1010 to 7.22 × 1011 molecules cm−3 s (0.5–4.9 d of atmospheric aging). In this study, the effects of NH3 gas on the secondary organic aerosol (SOA) formation of α-pinene by dark ozonolysis and photooxidation were investigated using the newly-developed flow reactor. For both dark α-pinene ozonolysis and photooxidation, higher SOA yields were observed in the presence of NH3 than in the absence of NH3. At RH of ∼50%, the SOA yield for ozonolysis and photooxidation in the presence of NH3 increased by 23% and 15% relative to those in the absence of NH3. Similar effects were observed at lower and higher RH conditions. Fourier transform infrared spectroscopy analysis confirmed the presence of nitrogen-containing functional groups in SOA formed in the presence of NH3. The α-pinene SOA formed in the presence of NH3 showed higher absorption and fluorescence for UV-visible radiation than those formed in the absence of NH3.Display Omitted
Keywords: Secondary organic aerosol; α-Pinene; NH3; Flow reactor; Optical properties; Brown carbon;
An investigation on the effect of street morphology to ambient air quality using six real-world cases by Jialei Shen; Zhi Gao; Wowo Ding; Ying Yu (85-101).
Street canyons are vulnerable to air pollution mainly caused by vehicle emissions, which are therefore closely related to pedestrians’ health. Previous studies have showed that air quality in street canyons is associated with street morphology, though the majority of them have focused on idealized street models. This paper attempts to investigate the relationship of street morphology to air quality for 6 irregular real-world cases selected from America, Europe, and China, i.e. Manhattan, Paris, Barcelona, Berlin, London and Nanjing. Each street is analyzed as a set of slices to propose a couple of morphology indices for quantitatively assessing the actual street morphology. Pollutant transport rate of mean flows and turbulent diffusion, net escape velocity and age of air are obtained from computational fluid dynamics (CFD) simulations to assess the ventilations and pollutant dispersion within street canyons with a parallel approaching wind. The results show that the street morphology characteristics, including the street width, lateral openings and intersections, are closely related to the air flows in street canyons. The air quality improves with a decreasing aspect ratio of central street owing to a larger vertical exchange through the street roof, which suggests an open central street is of better air quality. The lateral openings and intersections of streets have important effects on the air flows in street canyons, and the effects are particularly pronounced when the street widths are similar. The street continuity ratio indicates street continuity. It relates to the openings and the symmetry of a street and impacts on the air flows and pollutant dispersion through the lateral openings of the central street. The street spatial closure ratio is determined by the street continuity ratio and the aspect ratio of the central street. When the aspect ratio of central street is not excessively high, higher values of street continuity ratio and spatial closure ratio can lead to a stronger channel flow in street canyons and improve the air quality. The octagon intersections are favorable for air flowing through the lateral openings and improve the channel flows. The oblique intersections can also greatly improve the street ventilations, mainly due to the enhanced air flows through the lateral openings and the increased turbulent diffusion through the street roofs.
Keywords: Street morphology; Urban form; Street ventilation; Pollutant dispersion; Air quality; CFD simulation;
Dynamic evaluation of two decades of WRF-CMAQ ozone simulations over the contiguous United States by Marina Astitha; Huiying Luo; S. Trivikrama Rao; Christian Hogrefe; Rohit Mathur; Naresh Kumar (102-116).
Dynamic evaluation of the fully coupled Weather Research and Forecasting (WRF)– Community Multi-scale Air Quality (CMAQ) model ozone simulations over the contiguous United States (CONUS) using two decades of simulations covering the period from 1990 to 2010 is conducted to assess how well the changes in observed ozone air quality are simulated by the model. The changes induced by variations in meteorology and/or emissions are also evaluated during the same timeframe using spectral decomposition of observed and modeled ozone time series with the aim of identifying the underlying forcing mechanisms that control ozone exceedances and making informed recommendations for the optimal use of regional-scale air quality models. The evaluation is focused on the warm season's (i.e., May–September) daily maximum 8-hr (DM8HR) ozone concentrations, the 4th highest (4th) and average of top 10 DM8HR ozone values (top10), as well as the spectrally-decomposed components of the DM8HR ozone time series using the Kolmogorov-Zurbenko (KZ) filter. Results of the dynamic evaluation are presented for six regions in the U.S., consistent with the National Oceanic and Atmospheric Administration (NOAA) climatic regions. During the earlier 11-yr period (1990–2000), the simulated and observed regional average trends are not statistically significant. During the more recent 2000–2010 period, all observed trends are statistically significant and WRF-CMAQ captures the observed downward trend in the Southwest and Midwest but under-predicts the downward trends in observations for the other regions. Observational analysis reveals that it is the magnitude of the long-term forcing that dictates the maximum ozone exceedance potential; there is a strong linear relationship between the long-term forcing and the 4th highest or the average of the top10 ozone concentrations in both observations and model output. This finding indicates that improving the model's ability to reproduce the long-term component will also enable better simulation of ozone extreme values that are of interest to regulatory agencies.
Keywords: Model evaluation; WRF-CMAQ; Spectral decomposition; Ozone trends; Ozone design value; Decadal simulations;
Evaluating the effectiveness of joint emission control policies on the reduction of ambient VOCs: Implications from observation during the 2014 APEC summit in suburban Beijing by Kun Li; Junling Li; Weigang Wang; Shengrui Tong; John Liggio; Maofa Ge (117-127).
Ambient volatile organic compounds (VOCs) at a suburban Beijing site were on-line detected using proton transfer reaction-mass spectrometry (PTR-MS) during autumn of 2014, near the location of the Asia-Pacific Economic Cooperation (APEC) summit. During the APEC summit, the Chinese government enacted strict emission control policies. It was found that VOC concentrations only slightly decreased during the first emission control period (EC I), when control policies were performed in Beijing and 5 cities along the Tai-hang Mountains. However, most of the VOCs (10 out of 12 non-biogenic species) significantly decreased (more than 40%) during the second emission control period (EC II), when control policies were carried out in 16 cities including Beijing, Tianjin, 8 cities of Hebei province and 6 cities of Shandong province. Also the ratio of toluene and benzene decreased during EC II, likely because the emission control policies changed the proportions of different anthropogenic sources. Using the positive matrix factorization (PMF) source apportionment method, five factors are analyzed: (1) vehicle + fuel, (2) solvent, (3) biomass burning, (4) secondary, and (5) background + long-lived. Among them, vehicle + fuel, solvent and biomass burning contribute most of the VOCs concentrations (60%–80%) during the polluted periods and are affected most by emission control policies. During EC II, the reductions of vehicle + fuel, solvent, biomass burning and secondary species were all no less than 50%. Overall, when emission control policies were carried out in many North China Plain (NCP) cities (i.e. EC II), the VOC concentrations of suburban Beijing markedly decreased. This indicates the cross-regional joint-control policies have a large influence on reductions of organic gas species. The findings of this study have vital implications for helping formulate effective emission control policies in China and other countries.
Keywords: Volatile organic compounds; Asia-pacific economic cooperation; Emission control; Proton transfer reaction-mass spectrometry; Positive matrix factorization;
Bayesian identification of a single tracer source in an urban-like environment using a deterministic approach by Fei Xue; Xiaofeng Li; Weirong Zhang (128-138).
This paper presents a two-step deterministic approach for identifying an unknown point source with a constant emission rate in built-up urban areas. The analytic form of the marginal posterior probability density function of the source location is derived to estimate the source location. The emission rate is then estimated using the conditional posterior distribution. Such a procedure deconstructs the calculation of the joint posterior distribution of the source parameters into calculations of two separate distributions and can thus be easily calculated directly and accurately without stochastic sampling. The proposed method is tested using real data obtained in two wind tunnel scenarios of contaminant dispersion in typical urban geometries represented by block arrays. Computational fluid dynamics (CFD) modeling and the adjoint equations are used to calculate the building-resolving source-receptor relationship required in the identification. The estimated source parameters in both cases are close to true values. In both cases, the source locations are identified with errors less than half of the block size, and the emission rates are well estimated, with only slight overestimation. Moreover, in this paper, we test two potential performance indicators for a posteriori evaluation of the credibility of a certain estimation. One indicator is the size of the highest probability density region, and the other is the angle between the observed and predicted concentration vectors, which is derived from the analytic form of the marginal posterior distribution of the source location. Synthetic concentration data are generated to test the validity of both indicators. It is found that the former is not appropriate for denoting the credibility of estimations but that the latter shows a strong correlation with estimation performance and is likely to be an effective performance indicator for Bayesian source term estimation.
Keywords: Source term estimation; Bayesian inference; Performance evaluation; Urban dispersion; CFD;
8-Year ground-based observational analysis about the seasonal variation of the aerosol-cloud droplet effective radius relationship at SGP site by Yanmei Qiu; Chuanfeng Zhao; Jianping Guo; Jiming Li (139-146).
Previous studies have shown the negative or positive relationship between cloud droplet effective radius ( r e ) and aerosol amount based on limited observations, indicative of the uncertainties of this relationship caused by many factors. Using 8-year ground-based cloud and aerosol observations at Southern Great Plain (SGP) site in Oklahoma, US, we here analyze the seasonal variation of aerosol effect on low liquid cloud r e . It shows positive instead of negative AOD- r e relationship in all seasons except summer. Potential contribution to AOD- r e relationship from the precipitable water vapor (PWV) has been analyzed. Results show that the AOD- r e relationship is indeed negative in low PWV condition regardless of seasonality, but it turns positive in high PWV condition for all seasons other than summer. The most likely explanation for the positive AOD-re relationship in high PWV condition for spring, fall and winter is that high PWV could promote the growth of cloud droplets by providing sufficient water vapor. The different performance of AOD- r e relationship in summer could be related to the much heavier aerosol loading, which makes the PWV not sufficient any more so that the droplets compete water with each other. By limiting the variation of other meteorological conditions such as low tropospheric stability and wind speed near cloud bases, further analysis shows that higher PWVs not only help change AOD- r e relationship from negative to positive, but also make cloud depth and cloud top height higher.
Keywords: Low clouds; Aerosol-cloud interaction; Precipitable water vapor; SGP site;
A candidate framework for PM2.5 source identification in highly industrialized urban-coastal areas by Vinícius Lionel Mateus; Adriana Gioda (147-164).
The variability of PM sources and composition impose tremendous challenges for police makers in order to establish guidelines. In urban PM, sources associated with industrial processes are among the most important ones. In this study, a 5-year monitoring of PM2.5 samples was carried out in an industrial district. Their chemical composition was strategically determined in two campaigns in order to check the effectiveness of mitigation policies. Gaseous pollutants (NO2, SO2, and O3) were also monitored along with meteorological variables. The new method called Conditional Bivariate Probability Function (CBPF) was successfully applied to allocate the observed concentration of criteria pollutants (gaseous pollutants and PM2.5) in cells defined by wind direction-speed which provided insights about ground-level and elevated pollution plumes. CBPF findings were confirmed by the Theil-Sen long trend estimations for criteria pollutants. By means of CBPF, elevated pollution plumes were detected in the range of 0.54–5.8 μg m−3 coming from a direction associated to stacks. With high interpretability, the use of Conditional Inference Trees (CIT) provided both classification and regression of the speciated PM2.5 in the two campaigns. The combination of CIT and Random Forests (RF) point out NO 3 − and Ca+2 as important predictors for PM2.5. The latter predictor mostly associated to non-sea-salt sources, given a nss-Ca2+ contribution equal to 96%.
Keywords: Coastal urban atmosphere; Conditional bivariate probability function; Conditional inference trees; Secondary inorganic aerosols; PM2.5; Steelworks;
A study of the combined impact of boundary layer height and near-surface meteorology on the CO diurnal cycle at a low mountaintop site using simultaneous lidar and in-situ observations by S. Pal; T.R. Lee; S.F.J. De Wekker (165-179).
Evaluations of air pollutants and trace gas measurements over mountaintop sites and their application in inverse transport models to estimate regional scale fluxes are oftentimes challenging due to the influences associated with atmospheric transport at both local and regional scales. The objective of this study is to investigate the diurnal cycle pattern of CO mixing ratio over a low mountaintop influenced by: (1) two different convective boundary layer (CBL) regimes (shallow and deep) and associated growth rates over the mountaintop, (2) the combined effect of a deep CBL with and without diurnal wind shift, and (3) slope flows and associated air mass transport. For this purpose, we used simultaneous measurements of lidar-derived CBL heights, standard meteorological variables, and CO2 and CO mixing ratio from Pinnacles, a mountaintop monitoring site in the Appalachian Mountains. We used both water vapor and CO2 mixing ratio as tracers for upslope flow air masses. We used case studies to focus on two different scenarios of daytime CO mixing ratio variability: (1) a gradual increase in the morning with a maximum in the afternoon, and (2) a gradual decrease in the morning with a minimum in the late afternoon. The second scenario is similar to the CO variability observed atop tall towers in flat terrain.Using the lidar-derived CBL height evolution and in situ CO, CO2 and meteorological measurements over the mountaintop, we found that the CBL height dynamics, regional scale wind shift, and upslope flow air masses arriving at the mountaintop in the morning affect the CO mixing ratio variability during the remaining part of the diurnal cycle. These findings help introduce a conceptual framework that can explain and differentiate the opposite patterns (i.e. daytime increase versus daytime decrease) in the CO diurnal cycles over a mountaintop site affected by upslope flows and provide new roadmaps for monitoring and assimilating trace gas mixing ratios into applications requiring regionally-representative measurements.Display Omitted
Keywords: Air pollution; Carbon monoxide; Convective boundary layer height; Lidar; Mountaintop; Upslope flow;
Ozone, water vapor, and temperature anomalies associated with atmospheric blocking events over Eastern Europe in spring - summer 2010 by S.A. Sitnov; I.I. Mokhov; A.R. Lupo (180-194).
Using data from the AIRS satellite instrument (V6, L3), ozone, water vapor (WV), and temperature anomalies associated with the relatively short spring atmospheric blocking event and anomalously prolonged summer block over European Russia (ER) in 2010 are analyzed. Within the domain of the blocking anticyclones, negative total column ozone (TCO) anomalies and positive total column water vapor (TCWV) anomalies reaching the values of −25 and −32 Dobson Units (DU) and 10 and 11 kg m−2 during the spring and summer blocks are observed, respectively. Conversely, within the regions adjacent to the anticyclones to the west and east, positive TCO anomalies (77 and 45 DU) and negative TCWV anomalies (−3 and −4 kg m−2) are found. These TCO and TCWV anomalies are conditioned by the regional atmospheric circulation associated with the strong omega-type blocking. The TCO deficit and TCWV surplus within the atmospheric blocking domain are explained primarily by the poleward advection of subtropical air with low TCO and high TCWV content and tropopause uplift. The TCO and TCWV anomalies are also associated with quasi-stationary Rossby wave trains that accompanied these blocking events. An analysis of the anomaly vertical structure shows that the marked TCO decrease is primarily due to the lower stratospheric ozone decrease, while the strong TCWV increase is mainly the result of an increase of lower tropospheric WV content. The possible role of photochemical ozone destruction in the lower stratosphere due to WV advection within the blocked regions is also discussed. Vertical profiles of the thermal anomalies during both atmospheric blocking events reveal dipole-like structures characterized by positive temperature anomalies in the troposphere and negative anomalies in the lower stratosphere.
Keywords: Ozone; Water vapor; Temperature; Atmospheric blocking; AIRS;
A methodology to link national and local information for spatial targeting of ammonia mitigation efforts by E.J. Carnell; T.H. Misselbrook; A.J. Dore; M.A. Sutton; U. Dragosits (195-204).
The effects of atmospheric nitrogen (N) deposition are evident in terrestrial ecosystems worldwide, with eutrophication and acidification leading to significant changes in species composition. Substantial reductions in N deposition from nitrogen oxides emissions have been achieved in recent decades. By contrast, ammonia (NH3) emissions from agriculture have not decreased substantially and are typically highly spatially variable, making efficient mitigation challenging. One solution is to target NH3 mitigation measures spatially in source landscapes to maximize the benefits for nature conservation. The paper develops an approach to link national scale data and detailed local data to help identify suitable measures for spatial targeting of local sources near designated Special Areas of Conservation (SACs). The methodology combines high-resolution national data on emissions, deposition and source attribution with local data on agricultural management and site conditions.Application of the methodology for the full set of 240 SACs in England found that agriculture contributes ∼45 % of total N deposition. Activities associated with cattle farming represented 54 % of agricultural NH3 emissions within 2 km of the SACs, making them a major contributor to local N deposition, followed by mineral fertiliser application (21 %). Incorporation of local information on agricultural management practices at seven example SACs provided the means to correct outcomes compared with national-scale emission factors. The outcomes show how national scale datasets can provide information on N deposition threats at landscape to national scales, while local-scale information helps to understand the feasibility of mitigation measures, including the impact of detailed spatial targeting on N deposition rates to designated sites.
Keywords: Ammonia; Dry deposition; Emission abatement; Nitrogen; UK;
Elements and inorganic ions as source tracers in recent Greenland snow by Alexandra M. Lai; Martin M. Shafer; Jack E. Dibb; Chris M. Polashenski; James J. Schauer (205-215).
Atmospheric transport of aerosols leads to deposition of impurities in snow, even in areas of the Arctic as remote as Greenland. Major ions (e.g. Na+, Ca2+, NH4 +, K+, SO4 2−) are frequently used as tracers for common aerosol sources (e.g. sea spray, dust, biomass burning, anthropogenic emissions). Trace element data can supplement tracer ion data by providing additional information about sources. Although many studies have considered either trace elements or major ions, few have reported both. This study determined total and water-soluble concentrations of 31 elements (Al, As, Ca, Cd, Ce, Co, Cr, Dy, Eu, Fe, Gd, K, La, Mg, Mn, Na, Nb, Nd, Pb, Pr, S, Sb, Si, Sm, Sn, Sr, Ti, V, U, Y, Zn) in shallow snow pits at 22 sampling sites in Greenland, along a transect from Summit Station to sites in the northwest. Black carbon (BC) and inorganic ions were measured in colocated samples. Sodium, which is typically used as a tracer of sea spray, did not appear to have any non-marine sources. The rare earth elements, alkaline earth elements (Mg, Ca, Sr), and other crustal elements (Fe, Si, Ti, V) were not enriched above crustal abundances relative to Al, indicating that these elements are primarily dust sourced. Calculated ratios of non-sea salt Ca (nssCa) to estimated dust mass affirm the use of nssCa as a dust tracer, but suggest up to 50% uncertainty in that estimate in the absence of other crustal element data. Crustal enrichment factors indicated that As, Cd, Pb, non-sea-salt S, Sb, Sn, and Zn were enriched in these samples, likely by anthropogenic sources. Principal component analysis indicated more than one crustal factor, and a variety of factors related to anthropogenically enriched elements. Analysis of trace elements alongside major tracer ions does not change interpretation of ion-based source attribution for sources that are well-characterized by ions, but is valuable for assessing uncertainty in source attribution and identifying sources not represented by major ions.
Keywords: Greenland; Snow; Chemical composition; Trace elements; Dust;
The innovative concept of three-dimensional hybrid receptor modeling by A. Stojić; S. Stanišić Stojić (216-223).
The aim of this study was to improve the current understanding of air pollution transport processes at regional and long-range scale. For this purpose, three-dimensional (3D) potential source contribution function and concentration weighted trajectory models, as well as new hybrid receptor model, concentration weighted boundary layer (CWBL), which uses a two-dimensional grid and a planetary boundary layer height as a frame of reference, are presented. The refined approach to hybrid receptor modeling has two advantages. At first, it considers whether each trajectory endpoint meets the inclusion criteria based on planetary boundary layer height, which is expected to provide a more realistic representation of the spatial distribution of emission sources and pollutant transport pathways. Secondly, it includes pollutant time series preprocessing to make hybrid receptor models more applicable for suburban and urban locations. The 3D hybrid receptor models presented herein are designed to identify altitude distribution of potential sources, whereas CWBL can be used for analyzing the vertical distribution of pollutant concentrations along the transport pathway.
Keywords: PSCF; CWT; Three-dimensional hybrid receptor models; PM2.5; VOC;
Simulated nutrient dissolution of Asian aerosols in various atmospheric waters: Potential links to marine primary productivity by Lingyan Wang; Yanfeng Bi; Guosen Zhang; Sumei Liu; Jing Zhang; Zhaomeng Xu; Jingling Ren; Guiling Zhang (224-238).
To probe the bioavailability and environmental mobility of aerosol nutrient elements (N, P, Si) in atmospheric water (rainwater, cloud and fog droplets), ten total suspended particulate (TSP) samples were collected at Fulong Mountain, Qingdao from prevailing air mass trajectory sources during four seasons. Then, a high time-resolution leaching experiment with simulated non-acidic atmospheric water (non-AAW, Milli-Q water, pH 5.5) and subsequently acidic atmospheric water (AAW, hydrochloric acid solution, pH 2) was performed. We found that regardless of the season or source, a monotonous decreasing pattern was observed in the dissolution of N, P and Si compounds in aerosols reacted with non-AAW, and the accumulated dissolved curves of P and Si fit a first-order kinetic model. No additional NO3 − + NO2 − dissolved out, while a small amount of NH4 + in Asian dust (AD) samples was released in AAW. The similar dissolution behaviour of P and Si from non-AAW to AAW can be explained by the Transition State Theory. The sources of aerosols related to various minerals were the natural reasons that affected the amounts of bioavailable phosphorus and silicon in aerosols (i.e., solubility), which can be explained by the dissolution rate constant of P and Si in non-AAW with lower values in mineral aerosols. The acid/particle ratio and particle/liquid ratio also have a large effect on the solubility of P and Si, which was implied by Pearson correlation analysis. Acid processing of aerosols may have great significance for marine areas with limited P and Si and post-acidification release increases of 1.1–10-fold for phosphorus and 1.2–29-fold for silicon. The decreasing mole ratio of P and Si in AAW indicates the possibility of shifting from a Si-limit to a P-limit in aerosols in the ocean, which promotes the growth of diatoms prior to other algal species.
Keywords: Nutrient dissolution; Asian aerosol; Solubility; Atmospheric water; Yellow Sea;
Effects of industrial and agricultural waste amendment on soil greenhouse gas production in a paddy field in Southeastern China by Weiqi Wang; Suvadip Neogi; Derrick Y.F. Lai; Congsheng Zeng; Chun Wang; Dongping Zeng (239-249).
Controlling the production and subsequent emissions of greenhouse gases (GHGs) from paddy fields is crucial to minimize the climatic impacts arising from crop production. The application of chemical or biological amendments is one possible way to limit the production of GHGs in paddy soils. Yet, few existing studies have examined the impacts of applying fertilizers originated from industrial and agricultural wastes on soil GHG production and its governing factors in subtropical paddy fields. In this study, we examined the effects of various agricultural and industrial amendments, including biochar, steel slag, shell slag, gypsum slag, and slag-derived silicate and calcium fertilizers, on the production potential of GHGs in an early paddy field in southeast China. The mean CO2 production rates from soils amended with steel slag as well as silicate and calcium fertilizers were significantly higher than those of the controls by 13.4% and 18.6%, respectively (P < 0.05). Mean soil CH4 production rates from the plots amended with steel slag, biochar, shell slag, and gypsum slag were significantly lower than those of the controls by 42.5%, 36.1%, 60.8%, and 61.8%, respectively (P < 0.05). Meanwhile, we found no significant difference in mean soil N2O production rates between the control and any of the treatments (P > 0.05). Overall, the soil production rate of CO2 was positively correlated with that of CH4 (P < 0.05), but negatively correlated with that of N2O (P < 0.05). When compared to the controls, the ratio of soil CO2:CH4 production increased significantly in the plots receiving biochar, and silicate and calcium fertilizer amendments (P < 0.05), while that of CO2:N2O production increased significantly only in the biochar-amended plots. Soil CH4:N2O production ratio decreased significantly in the plots amended with steel slag and gypsum slag, as compared to the controls (P < 0.05). Our results suggest that the application of biochar, shell slag and gypsum slag would help reduce greenhouse gas production and mitigate climate change impacts of rice cultivation, largely attributable to the reduction in methanogenesis.
Keywords: Rice paddy; Greenhouse gas production; Steel slag; Biochar; Shell slag; Gypsum slag;
Application of VUV-PIMS coupled with GC-MS in chemical characterization, identification and comparative analysis of organic components in both vehicular-derived SOA and haze particles by Peng Zhang; Pengkun Ma; Haixu Zhang; Jinian Shu; Bo Yang; Zhen Li (250-258).
Gasoline vehicle exhaust is a significant source of volatile organic compounds (VOCs) in megacities. In this study, chemical characterization of secondary aerosol particles from the oxidation of gasoline vehicular exhaust by O3, OH, and NO3 radicals and the airborne aerosol particles collected during a heavy haze episode (23–25 December 2015) in Beijing were elaborately investigated. The secondary organic aerosols (SOAs) collected from the exhaust and airborne aerosol particles were characterized with a newly built vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) after thermal desorption, and identified by gas chromatography mass spectrometry (GC-MS). The obtained photoionization mass spectra revealed that the SOAs from the oxidation of gasoline vehicular exhaust and airborne aerosol particles possess a series of common characteristic mass peaks at m/z 98, 112, 126, and 140. The components at m/z 98, 112, 126, 140 were further identified to be carbonyl species after PFBHA derivatization followed by GC-MS analyses. The carbonyl species from exhaust SOAs were found to be responsible for 51.7%, 57.5%, 36.3%, and 27.9% of the chemical components in haze particles at m/z 98, 112, 126, and 140, respectively, which indicates that these SOA components from the oxidation of gasoline vehicular exhaust are a major factor that affects the air quality in Beijing. Among the exhaust SOAs, the carbonyl species detected simultaneously in two (P(O3/OH)) or three kinds of exhaust oxidation reactions (P(O3/NO3/OH)) make a significant contributions to these carbonyl species in haze particles (10.6% for m/z 98, 18.3% for m/z 112, 23.4% for m/z 126, and 20.5% for m/z 140). These results implies that the unsaturated VOCs (i.e. alkenes) from exhaust may be one kind of important SOA precursor and that their chemical degradation in the atmosphere may have an important impact on urban air quality in heavy polluted cities such as Beijing, especially during severe winter haze weather.Display Omitted
Keywords: Gasoline vehicle exhaust; Secondary organic aerosols; Haze; OH/NO3/O3; Derivatization;
Influence of biomass burning on mixing state of sub-micron aerosol particles in the North China Plain by Simonas Kecorius; Nan Ma; Monique Teich; Dominik van Pinxteren; Shenglan Zhang; Johannes Gröβ; Gerald Spindler; Konrad Müller; Yoshiteru Iinuma; Min Hu; Hartmut Herrmann; Alfred Wiedensohler (259-269).
Particulate emissions from crop residue burning decrease the air quality as well as influence aerosol radiative properties on a regional scale. The North China Plain (NCP) is known for the large scale biomass burning (BB) of field residues, which often results in heavy haze pollution episodes across the region. We have been able to capture a unique BB episode during the international CAREBeijing-NCP intensive field campaign in Wangdu in the NCP (38.6°N, 115.2°E) from June to July 2014. It was found that aerosol particles originating from this BB event showed a significantly different mixing state compared with clean and non-BB pollution episodes. BB originated particles showed a narrower probability density function (PDF) of shrink factor (SF). And the maximum was found at shrink factor of 0.6, which is higher than in other episodes. The non-volatile particle number fraction during the BB episode decreased to 3% and was the lowest measured value compared to all other predefined episodes. To evaluate the influence of particle mixing state on aerosol single scattering albedo (SSA), SSA at different RHs was simulated using the measured aerosol physical-chemical properties. The differences between the calculated SSA for biomass burning, clean and pollution episodes are significant, meaning that the variation of SSA in different pollution conditions needs to be considered in the evaluation of aerosol direct radiative effects in the NCP. And the calculated SSA was found to be quite sensitive on the mixing state of BC, especially at low-RH condition. The simulated SSA was also compared with the measured values. For all the three predefined episodes, the measured SSA are very close to the calculated ones with assumed mixing states of homogeneously internal and core-shell internal mixing, indicating that both of the conception models are appropriate for the calculation of ambient SSA in the NCP.
Keywords: Biomass burning; Sub-micron aerosol particles; Mixing state;
Contribution of time-activity pattern and microenvironment to black carbon (BC) inhalation exposure and potential internal dose among elementary school children by Hyeran Jeong; Donguk Park (270-279).
The aims of this study were to quantify the contributions of activities or microenvironments (MEs) to daily total exposure to and potential dose of black carbon (BC). Daily BC exposures (24-h) were monitored using a micro-aethalometer micoAeth AE51 with forty school-aged children living in an urban area in Korea from August 2015 to January 2016. The children's time-activity patterns and the MEs they visited were investigated by means of a time-activity diary (TAD) and follow-up interviews with the children and their parents. Potential inhaled dose was estimated by multiplying the airborne BC concentrations (μg/m3) we monitored for the time the children spent in a particular ME by the inhalation rate (IR, m3/h) for the time-activity performed. The contribution of activities and MEs to overall daily exposure to and potential dose of BC was quantified. Overall mean daily potential dose was equal to 24.1 ± 10.6 μg/day (range: 6.6–46.3 μg/day). The largest contribution to BC exposure and potential dose (51.9% and 41.7% respectively) occurred in the home thanks to the large amount of time spent there. Transportation was where children received the most intense exposure to (14.8%) and potential dose (20.2%) of BC, while it accounted for 7.6% of daily time. School on weekdays during the semester was responsible for 20.3% of exposure and 22.5% of potential dose. Contribution to BC exposure and potential dose was altered by several time-activity parameters, such as type of day (weekdays vs. weekends; school days vs. holidays), season, and gender. Traveling by motor vehicle and subway showed more elevated exposure or potential dose intensity on weekdays or school days, probably influenced by the increased surrounding traffic volumes on these days compared to on weekends or holidays. This study may be used to prioritize targets for minimizing children's exposure to BC and to indicate outcomes of BC control strategies.
Keywords: Black carbon (BC); Exposure; Potential inhaled dose; Time-activity pattern; Microenvironment (ME); Contribution; Intensity;
Isotopic signatures of anthropogenic CH4 sources in Alberta, Canada by M. Lopez; O.A. Sherwood; E.J. Dlugokencky; R. Kessler; L. Giroux; D.E.J. Worthy (280-288).
A mobile system was used for continuous ambient measurements of stable CH4 isotopes (12CH4 and 13CH4) and ethane (C2H6). This system was used during a winter mobile campaign to investigate the CH4 isotopic signatures and the C2H6/CH4 ratios of the main anthropogenic sources of CH4 in the Canadian province of Alberta. Individual signatures were derived from δ13CH4 and C2H6 measurements in plumes arriving from identifiable single sources. Methane emissions from beef cattle feedlots (n = 2) and landfill (n = 1) had δ13CH4 signatures of −66.7 ± 2.4‰ and −55.3 ± 0.2‰, respectively. The CH4 emissions associated with the oil or gas industry had distinct δ13CH4 signatures, depending on the formation process. Emissions from oil storage tanks (n = 5) had δ13CH4 signatures ranging from −54.9 ± 2.9‰ to −60.6 ± 0.6‰ and non-detectable C2H6, characteristic of secondary microbial methanogenesis in oil-bearing reservoirs. In contrast, CH4 emissions associated with natural gas facilities (n = 8) had δ13CH4 signatures ranging from −41.7 ± 0.7‰ to −49.7 ± 0.7‰ and C2H6/CH4 molar ratios of 0.10 for raw natural gas to 0.04 for processed/refined natural gas, consistent with thermogenic origins. These isotopic signatures and C2H6/CH4 ratios have been used for source discrimination in the weekly atmospheric measurements of stable CH4 isotopes over a two-month winter period at the Lac La Biche (LLB) measurement station, located in Alberta, approximately 200 km northeast of Edmonton. The average signature of −59.5 ± 1.4‰ observed at LLB is likely associated with transport of air after passing over oil industry sources located south of the station.
Keywords: Methane isotopic signature; AirCore; Oil and natural gas industry; Plume mapping;
Long-term quantitative field study of New Particle Formation (NPF) events as a source of Cloud Condensation Nuclei (CCN) in the urban background of Vienna by C. Dameto de España; A. Wonaschütz; G. Steiner; B. Rosati; A. Demattio; H. Schuh; R. Hitzenberger (289-298).
Many studies have indicated New Particle Formation (NPF) events as an important source of CCN in the atmosphere. However, most of these studies are based on indirect determination of CCN concentrations or were of rather short duration. In this study, we present long-term measurements of CCN concentrations and particle number size distributions performed in the urban background of Vienna, Austria, spanning a period of two years. NPF events occurred on 70 of the 539 measurement days. For 38 of these events, concurrent CCN concentrations (measured at 0.5% supersaturation) are available. Direct comparisons of absolute CCN concentrations before and after an event, however, are inconclusive as other influences can lead to changes in CCN concentrations. In this study, we developed criteria to take local emissions of ultrafine particles, atmospheric mixing conditions and changes in air mass into account. A new normalization procedure (CCN/PM2.5) is introduced to account for dilution and concentration effects due to changes in boundary layer height. Other possible influences, such as weather conditions and traffic emissions were accounted for by tracking wind direction and velocity, as well as black carbon (BC) mass concentrations. On 15 event days, all criteria to exclude other influences were met. On 14 days, NPF was found to be a source of CCN (at 0.5% supersaturation), with concentration increases by up to 143%.
Keywords: Long-term CCN study; Cloud condensation nuclei; New particle formation events; Urban aerosol;
CCN characteristics over a tropical coastal station during south-west monsoon: observations and closure studies by V. Jayachandran; Vijayakumar S. Nair; S. Suresh Babu (299-308).
Number concentration measurements of cloud condensation nuclei (CCN) at five supersaturation values between 0.2 and 1.0% were made from a coastal site (Thiruvananthapuram) of peninsular India using a single column CCN counter during the summer monsoon period (June–September) of 2013 and 2014. The CCN concentration over this site showed diurnal variations of high values during nighttime and low values during daytime in association with the change in mesoscale circulation patterns. The inter-annual variations of CCN (CCN0.4% = 2,232 ± 672 cm−3 during August 2013 and CCN0.4% = 941 ± 325 cm−3 during August 2014) are mostly associated with the varying intensity of monsoon rainfall. The variation of CCN number concentration with supersaturation is found to be steeper during nighttime (indicating a less CCN active aerosol system) than during daytime (CCN active system). The CCN activation ratio estimated using simultaneous measurements of CCN and aerosol number (CN) concentration clearly depict the role of land-sea breeze circulations with higher values during daytime than the nighttime. The CCN number concentration predicted for different supersaturations, from measured aerosol number size distribution using Kohler theory, indicate the importance of the change in aerosol composition associated with different airmasses in a coastal environment.
Keywords: Cloud condensation nuclei; Aerosol-cloud interaction; Activation ratio; CCN prediction;
Regional and hemispheric influences on temporal variability in baseline carbon monoxide and ozone over the Northeast US by Y. Zhou; H. Mao; K. Demerjian; C. Hogrefe; J. Liu (309-324).
Interannual variability in baseline carbon monoxide (CO) and ozone (O3), defined as mixing ratios under minimal influence of recent and local emissions, was studied for seven rural sites in the Northeast US over 2001–2010. Annual baseline CO exhibited statistically significant decreasing trends (−4.3 to −2.3 ppbv yr−1), while baseline O3 did not display trends at any site. In examining the data by season, wintertime and springtime baseline CO at the two highest sites (1.5 km and 2 km asl) did not experience significant trends. Decadal increasing trends (∼2.55 ppbv yr−1) were found in springtime and wintertime baseline O3 in southern New Hampshire, which was associated with anthropogenic NOx emission reductions from the urban corridor. Biomass burning emissions impacted summertime baseline CO with ∼38% variability from wildfire emissions in Russia and ∼22% from Canada at five sites and impacted baseline O3 at the two high elevation sites only with ∼27% variability from wildfires in both Russia and Canada. The Arctic Oscillation was negatively correlated with summertime baseline O3, while the North Atlantic Oscillation was positively correlated with springtime baseline O3. This study suggested that anthropogenic and biomass burning emissions, and meteorological conditions were important factors working together to determine baseline O3 and CO in the Northeast U.S. during the 2000s.
Keywords: Baseline CO; Baseline O3; Temporal variability; Northeast U.S.; Emission; Meteorology;
Impact of evolving isoprene mechanisms on simulated formaldehyde: An inter-comparison supported by in situ observations from SENEX by Margaret R. Marvin; Glenn M. Wolfe; Ross J. Salawitch; Timothy P. Canty; Sandra J. Roberts; Katherine R. Travis; Kenneth C. Aikin; Joost A. de Gouw; Martin Graus; Thomas F. Hanisco; John S. Holloway; Gerhard Hübler; Jennifer Kaiser; Frank N. Keutsch; Jeff Peischl; Ilana B. Pollack; James M. Roberts; Thomas B. Ryerson; Patrick R. Veres; Carsten Warneke (325-336).
Isoprene oxidation schemes vary greatly among gas-phase chemical mechanisms, with potentially significant ramifications for air quality modeling and interpretation of satellite observations in biogenic-rich regions. In this study, in situ observations from the 2013 SENEX mission are combined with a constrained 0-D photochemical box model to evaluate isoprene chemistry among five commonly used gas-phase chemical mechanisms: CB05, CB6r2, MCMv3.2, MCMv3.3.1, and a recent version of GEOS-Chem. Mechanisms are evaluated and inter-compared with respect to formaldehyde (HCHO), a high-yield product of isoprene oxidation. Though underestimated by all considered mechanisms, observed HCHO mixing ratios are best reproduced by MCMv3.3.1 (normalized mean bias = −15%), followed by GEOS-Chem (−17%), MCMv3.2 (−25%), CB6r2 (−32%) and CB05 (−33%). Inter-comparison of HCHO production rates reveals that major restructuring of the isoprene oxidation scheme in the Carbon Bond mechanism increases HCHO production by only ∼5% in CB6r2 relative to CB05, while further refinement of the complex isoprene scheme in the Master Chemical Mechanism increases HCHO production by ∼16% in MCMv3.3.1 relative to MCMv3.2. The GEOS-Chem mechanism provides a good approximation of the explicit isoprene chemistry in MCMv3.3.1 and generally reproduces the magnitude and source distribution of HCHO production rates. We analytically derive improvements to the isoprene scheme in CB6r2 and incorporate these changes into a new mechanism called CB6r2-UMD, which is designed to preserve computational efficiency. The CB6r2-UMD mechanism mimics production of HCHO in MCMv3.3.1 and demonstrates good agreement with observed mixing ratios from SENEX (−14%). Improved simulation of HCHO also impacts modeled ozone: at ∼0.3 ppb NO, the ozone production rate increases ∼3% between CB6r2 and CB6r2-UMD, and rises another ∼4% when HCHO is constrained to match observations.
Keywords: Formaldehyde; Isoprene; Gas-phase chemical mechanisms; Box model; SENEX; Air quality;
Evaluation of the chemical composition and correlation between the calculated and measured odour concentration of odorous gases from a landfill in Beijing, China by Chuandong Wu; Jiemin Liu; Peng Zhao; Wenhui Li; Luchun Yan; Martin Piringer; Günther Schauberger (337-347).
Odorous gases emitted from landfills have always been a public concern, but studies evaluating the odour contribution and the correlation between the odour concentrations are limited. The objectives of this study were to assess the odour contribution and to correlate the measured odour concentration C OD with the calculated odour concentration SOAV, which was calculated as sum of individual odour activity value (OAV). Odorous air samples from a landfill in Beijing were collected seasonally and measured by both gas chromatography and an olfactometer. Different from previous studies, we measured the odour threshold of 51 detected compounds using a uniform methodology to minimize the imprecision of citing odour threshold from disparate literature. The odour threshold is used to convert the individual chemical concentration into the OAV, which is used as a surrogate of the odour concentration. Evaluation of the OAV revealed that hydrogen sulfide (65.9%), dimethyl sulfide (14.4%) and trimethylamine (8.6%) contributed the most to the odour at the landfill. Moreover, the correlation between the calculated odour concentration SOAV and the measured odour concentration C OD resulted in a linear regression equation of C OD = 6.28 SOAV (r = 0.914, n = 24, p < 0.01). Based on the scaling factor K = 6.28, the average ratio of calculated odour concentration to measured odour concentration could be improved from less than 0.2 to 1.1. By the calibration of the calculated odour concentration SOAV, it is possible to use continuous measurements of chemical concentrations to derive odour concentration for this site for monitoring purposes.Display Omitted
Keywords: Landfill; Ammonia; Odour threshold; Odour activity value; Odour concentration;
Concentrations and nitrogen isotope compositions of free amino acids in Pinus massoniana (Lamb.) needles of different ages as indicators of atmospheric nitrogen pollution by Yu Xu; Huayun Xiao (348-359).
Free amino acid δ15N values and concentrations of current-year new (new), current-year mature (middle-age) and previous-year (old) Pinus massoniana (Lamb.) needles were determined for five sites with different distances from a highway in a forest in Guiyang (SW China). Needle free amino acid concentrations decreased with increasing distance from the highway, and only the free amino acid concentrations (total free amino acid, arginine, γ-aminobutyric acid, valine, alanine and proline) in the middle-aged needles demonstrated a strong correlation with distance from the highway, indicating that free amino acid concentrations in middle-aged needles may be a more suitable indicator of nitrogen (N) deposition compared to new and old needles. Needle free amino acid δ15N values were more positive near the highway compared to the more distant sites and increased with increasing needle age, indicating that N deposition in this site may be dominated by isotopically heavy NOx-N from traffic emissions. In sites beyond 400 m from the highway, the δ15N values of total free amino acids, histidine, glutamine, proline, alanine, aspartate, isoleucine, lysine, arginine and serine in each age of needle were noticeably negative compared to their respective δ15N values near the highway. This suggested that needle free amino acid δ15N values from these sites were more affected by 15N-depleted atmospheric NHx-N from soil emissions. This result was further supported by the similarity in the negative moss δ15N values at these sites to the δ15N values of soil-derived NHx-N. Needle free amino acid δ15N values therefore have the potential to provide information about atmospheric N sources. We conclude that needle free amino acid concentrations are sensitive indicators of N deposition and that the age-related free amino acid δ15N values in needles can efficiently reflect atmospheric N sources. This would probably promote the application of the combined plant tissue amino acid concentration and δ15N analyses in N deposition bio-monitoring.
Keywords: Pinus massoniana Lamb.; Needles; Age; Free amino acid δ15N; Atmospheric N sources;
Observations of particle extinction, PM2.5 mass concentration profile and flux in north China based on mobile lidar technique by Lihui Lv; Wenqing Liu; Tianshu Zhang; Zhenyi Chen; Yunsheng Dong; Guangqiang Fan; Yan Xiang; Yawei Yao; Nan Yang; Baolin Chu; Man Teng; Xiaowen Shu (360-369).
Fine particle with diameter <2.5 μm (PM2.5) have important direct and indirect effects on human life and activities. However, the studies of fine particle were limited by the lack of monitoring data obtained with multiple fixed site sampling strategies. Mobile monitoring has provided a means for broad measurement of fine particles. In this research, the potential use of mobile lidar to map the distribution and transport of fine particles was discussed. The spatial and temporal distributions of particle extinction, PM2.5 mass concentration and regional transport flux of fine particle in the planetary boundary layer were investigated with the use of vehicle-based mobile lidar and wind field data from north China. Case studies under different pollution levels in Beijing were presented to evaluate the contribution of regional transport. A vehicle-based mobile lidar system was used to obtain the spatial and temporal distributions of particle extinction in the measurement route. Fixed point lidar and a particulate matter sampler were operated next to each other at the University of Chinese Academy of Science (UCAS) in Beijing to determine the relationship between the particle extinction coefficient and PM2.5 mass concentration. The correlation coefficient (R2) between the particle extinction coefficient and PM2.5 mass concentration was found to be over 0.8 when relative humidity (RH) was less than 90%. A mesoscale meteorological model, the Weather Research and Forecasting (WRF) model, was used to obtain profiles of the horizontal wind speed, wind direction and relative humidity. A vehicle-based mobile lidar technique was applied to estimate transport flux based on the PM2.5 profile and vertical profile of wind data. This method was applicable when hygroscopic growth can be neglected (relatively humidity<90%). Southwest was found to be the main pathway of Beijing during the experiments.
Keywords: Vehicle-based mobile lidar; Fine particle; PM2.5 profile; Flux;
Source apportionment of PM2.5 across China using LOTOS-EUROS by R. Timmermans; R. Kranenburg; A. Manders; C. Hendriks; A. Segers; E. Dammers; Q. Zhang; L. Wang; Z. Liu; L. Zeng; H. Denier van der Gon; M. Schaap (370-386).
China's population is exposed to high levels of particulate matter (PM) due to its strong economic growth and associated urbanization and industrialization. To support policy makers to develop cost effective mitigation strategies it is of crucial importance to understand the emission sources as well as formation routes responsible for high pollution levels. In this study we applied the LOTOS-EUROS model with its module to track the contributions of predefined source sectors to China for the year 2013 using the MEIC emission inventory. It is the first application of the model system to a region outside Europe. The source attribution was aimed to provide insight in the sector and area of origin of PM2.5 for the cities of Beijing and Shanghai. The source attribution shows that on average about half of the PM2.5 pollution in both cities originates from the municipality itself. About a quarter of the PM2.5 comes from the neighbouring provinces, whereas the remaining quarter is attributed to long range transport from anthropogenic and natural components. Residential combustion, transport, and industry are identified as the main sources with comparable contributions allocated to these sectors. The importance of the sectors varies throughout the year and differs slightly between the cities. During winter, urban contributions from residential combustion are dominant, whereas industrial and traffic contributions with a larger share of regional transport are more important during summer. The evaluation of the model results against satellite and in-situ observations shows the ability of the LOTOS-EUROS model to capture many features of the variability in particulate matter and its precursors in China. The model shows a systematic underestimation of particulate matter concentrations, especially in winter. This illustrates that modelling particulate matter remains challenging as it comes to components like secondary organic aerosol and suspended dust as well as emissions and formation of PM during winter time haze situations. All in all, the LOTOS-EUROS system proves to be a powerful tool for policy support applications outside Europe as the intermediate complexity of the model allows the assessment of the area and sector of origin over decadal time periods.
Keywords: PM2.5; Beijing; Shanghai; Chemistry transport model; Model evaluation;
Light absorption and the photoformation of hydroxyl radical and singlet oxygen in fog waters by R. Kaur; C. Anastasio (387-397).
The atmospheric aqueous-phase is a rich medium for chemical transformations of organic compounds, in part via photooxidants generated within the drops. Here we measure light absorption, photoformation rates and steady-state concentrations of two photooxidants – hydroxyl radical (•OH) and singlet molecular oxygen (1O2*) – in 8 illuminated fog waters from Davis, California and Baton Rouge, Louisiana. Mass absorption coefficients for dissolved organic compounds (MACDOC) in the samples are large, with typical values of 10,000–15,000 cm2 g-C−1 at 300 nm, and absorption extends to wavelengths as long as 450–600 nm. While nitrite and nitrate together account for an average of only 1% of light absorption, they account for an average of 70% of •OH photoproduction. Mean •OH photoproduction rates in fogs at the two locations are very similar, with an overall mean of 1.2 (±0.7) μM h−1 under Davis winter sunlight. The mean (±1σ) lifetime of •OH is 1.6 (±0.6) μs, likely controlled by dissolved organic compounds. Including calculated gas-to-drop partitioning of •OH, the average aqueous concentration of •OH is approximately 2 × 10−15 M (midday during Davis winter), with aqueous reactions providing approximately one-third of the hydroxyl radical source. At this concentration, calculated lifetimes of aqueous organics are on the order of 10 h for compounds with •OH rate constants of 1 × 1010 M−1 s−1 or higher (e.g., substituted phenols such as syringol (6.4 h) and guaiacol (8.4 h)), and on the order of 100 h for compounds with rate constants near 1 × 109 M−1 s−1 (e.g., isoprene oxidation products such as glyoxal (152 h), glyoxylic acid (58 h), and pyruvic acid (239 h)). Steady-state concentrations of 1O2* are approximately 100 times higher than those of •OH, in the range of (0.1–3.0) × 10−13 M. Since 1O2* is a more selective oxidant than •OH, it will only react appreciably with electron-rich species such as dimethyl furan (lifetime of 2.0 h) and substituted polycyclic aromatic hydrocarbons (e.g., 9,10-dimethylbenz[a]anthracene with a lifetime of 0.7 h). Comparing our current Davis samples with Davis fogs collected in the late 1990s shows a decrease in dissolved organic carbon content, similar mass absorption coefficients, lower •OH concentrations, but very similar 1O2* concentrations.
Keywords: Photooxidants; Atmospheric aqueous photochemistry; Aqueous secondary organic aerosol;
Allocating emissions to 4 km and 1 km horizontal spatial resolutions and its impact on simulated NOx and O3 in Houston, TX by Shuai Pan; Yunsoo Choi; Anirban Roy; Wonbae Jeon (398-415).
A WRF-SMOKE-CMAQ air quality modeling system was used to investigate the impact of horizontal spatial resolution on simulated nitrogen oxides (NOx) and ozone (O3) in the Greater Houston area (a non-attainment area for O3). We employed an approach recommended by the United States Environmental Protection Agency to allocate county-based emissions to model grid cells in 1 km and 4 km horizontal grid resolutions. The CMAQ Integrated Process Rate analyses showed a substantial difference in emissions contributions between 1 and 4 km grids but similar NOx and O3 concentrations over urban and industrial locations. For example, the peak NOx emissions at an industrial and urban site differed by a factor of 20 for the 1 km and 8 for the 4 km grid, but simulated NOx concentrations changed only by a factor of 1.2 in both cases. Hence, due to the interplay of the atmospheric processes, we cannot expect a similar level of reduction of the gas-phase air pollutants as the reduction of emissions. Both simulations reproduced the variability of NASA P-3B aircraft measurements of NOy and O3 in the lower atmosphere (from 90 m to 4.5 km). Both simulations provided similar reasonable predictions at surface, while 1 km case depicted more detailed features of emissions and concentrations in heavily polluted areas, such as highways, airports, and industrial regions, which are useful in understanding the major causes of O3 pollution in such regions, and to quantify transport of O3 to populated communities in urban areas. The Integrated Reaction Rate analyses indicated a distinctive difference of chemistry processes between the model surface layer and upper layers, implying that correcting the meteorological conditions at the surface may not help to enhance the O3 predictions. The model-observation O3 bias in our studies (e.g., large over-prediction during the nighttime or along Gulf of Mexico coastline), were due to uncertainties in meteorology, chemistry or other processes. Horizontal grid resolution is unlikely the major contributor to these biases.
Keywords: Fine resolution emissions; Spatial allocation; Ozone; CMAQ; Process analysis;
Evolution of air pollution source contributions over one decade, derived by PM10 and PM2.5 source apportionment in two metropolitan urban areas in Greece by E. Diapouli; M. Manousakas; S. Vratolis; V. Vasilatou; Th Maggos; D. Saraga; Th Grigoratos; G. Argyropoulos; D. Voutsa; C. Samara; K. Eleftheriadis (416-430).
Metropolitan Urban areas in Greece have been known to suffer from poor air quality, due to variety of emission sources, topography and climatic conditions favouring the accumulation of pollution. While a number of control measures have been implemented since the 1990s, resulting in reductions of atmospheric pollution and changes in emission source contributions, the financial crisis which started in 2009 has significantly altered this picture. The present study is the first effort to assess the contribution of emission sources to PM10 and PM2.5 concentration levels and their long-term variability (over 5–10 years), in the two largest metropolitan urban areas in Greece (Athens and Thessaloniki). Intensive measurement campaigns were conducted during 2011–2012 at suburban, urban background and urban traffic sites in these two cities. In addition, available datasets from previous measurements in Athens and Thessaloniki were used in order to assess the long-term variability of concentrations and sources. Chemical composition analysis of the 2011–2012 samples showed that carbonaceous matter was the most abundant component for both PM size fractions. Significant increase of carbonaceous particle concentrations and of OC/EC ratio during the cold period, especially in the residential urban background sites, pointed towards domestic heating and more particularly wood (biomass) burning as a significant source. PMF analysis further supported this finding. Biomass burning was the largest contributing source at the two urban background sites (with mean contributions for the two size fractions in the range of 24–46%). Secondary aerosol formation (sulphate, nitrate & organics) was also a major contributing source for both size fractions at the suburban and urban background sites. At the urban traffic site, vehicular traffic (exhaust and non-exhaust emissions) was the source with the highest contributions, accounting for 44% of PM10 and 37% of PM2.5, respectively. The long-term variability of emission sources in the two cities (over 5–10 years), assessed through a harmonized application of the PMF technique on recent and past year data, clearly demonstrates the effective reduction in emissions during the last decade due to control measures and technological development; however, it also reflects the effects of the financial crisis in Greece during these years, which has led to decreased economic activities and the adoption of more polluting practices by the local population in an effort to reduce living costs.Display Omitted
Keywords: PM10/PM2.5; PMF analysis; Biomass burning; Long-term source variability; Urban environment; Greek financial crisis;
Vertical variability of aerosol single-scattering albedo and equivalent black carbon concentration based on in-situ and remote sensing techniques during the iAREA campaigns in Ny-Ålesund by K.M. Markowicz; C. Ritter; J. Lisok; P. Makuch; I.S. Stachlewska; D. Cappelletti; M. Mazzola; M.T. Chilinski (431-447).
This work presents a methodology for obtaining vertical profiles of aerosol single scattering properties based on a combination of different measurement techniques. The presented data were obtained under the iAREA (Impact of absorbing aerosols on radiative forcing in the European Arctic) campaigns conducted in Ny-Ålesund (Spitsbergen) during the spring seasons of 2015–2017. The retrieval uses in-situ observations of black carbon concentration and absorption coefficient measured by a micro-aethalometer AE-51 mounted onboard a tethered balloon, as well as remote sensing data obtained from sun photometer and lidar measurements. From a combination of the balloon-borne in-situ and the lidar data, we derived profiles of single scattering albedo (SSA) as well as absorption, extinction, and aerosol number concentration. Results have been obtained in an altitude range from about 400 m up to 1600 m a.s.l. and for cases with increased aerosol load during the Arctic haze seasons of 2015 and 2016. The main results consist of the observation of increasing values of equivalent black carbon (EBC) and absorption coefficient with altitude, and the opposite trend for aerosol concentration for particles larger than 0.3 μm. SSA was retrieved with the use of lidar Raman and Klett algorithms for both 532 and 880 nm wavelengths. In most profiles, SSA shows relatively high temporal and altitude variability. Vertical variability of SSA computed from both methods is consistent; however, some discrepancy is related to Raman retrieval uncertainty and absorption coefficient estimation from AE-51. Typically, very low EBC concentration in Ny-Ålesund leads to large error in the absorbing coefficient. However, SSA uncertainty for both Raman and Klett algorithms seems to be reasonable, e.g. SSA of 0.98 and 0.95 relate to an error of ±0.01 and ± 0.025, respectively.
Keywords: Aerosol; Single-scattering albedo; Black carbon; Micro-aethalometer; Lidar; Arctic haze;
Molecular composition of organic aerosol over an agricultural site in North China Plain: Contribution of biogenic sources to PM2.5 by Xingru Li; Yusi Liu; Dong Li; Guoan Wang; Yu Bai; Heling Diao; Rongrong Shen; Bo Hu; Jinyuan Xin; Zirui Liu; Yuesi Wang; Xueqing Guo; Lili Wang (448-457).
Sugars and biogenic secondary organic aerosols (BSOAs) are substantial components of particulate organic matter, which affects regional and global air quality and climate. Fine particulate matter (PM2.5) samples were collected from 20 June to 30 July 2015 on a diurnal/nocturnal cycle in Yucheng, China in the North China Plain. The PM2.5 samples were analyzed for sugars and SOA tracers derived from biogenic volatile organic compounds (BVOCs) and other compounds, such as water soluble ions, element carbon (EC), organic carbon (OC) and water soluble organic carbon (WSOC). The quantified organic components accounted for 4.7% and 0.4% of the OC and PM2.5, respectively. SOA tracer concentrations were weakly higher during the day (101.6 ± 61.7 ng m−3) than at night (90.2 ± 41.5 ng m−3)(t = 0.610, P > 0.05), whereas sugar showed higher concentrations at night (227.0 ± 196.9 ng m−3) than during the day (177.9 ± 145.4 ng m−3)(t = −1.329, P > 0.05). Anhydro sugar (mannosan, galactosan, and levoglucosan) were the main components of the measured sugars and accounted for 58.5% and 75.6% of the daytime and nighttime measurements. The levoglucosan/mannosan ratios were 20.2 ± 12.9 and 17.6 ± 9.1 for the daytime and nighttime samples, respectively, indicating that crop residues, herbaceous plants and hardwood were the dominant types of biomass burned in the Yucheng region. Isoprene SOA tracers exhibited the highest levels among the measured SOA tracers, followed by α-pinene SOA tracers. The concentration of BSOC estimated using the tracer method was 3.9–1817.5 ng C m−3 and accounted for 0.1–26.0% of the OC. A clear negative correlation (r = 0.53) between isoprene-derived SOA and in-situ pH demonstrated that acid-catalyzed heterogeneous reactions can significantly enhance SOA mass. In addition, isoprene-derived SOA increased with the relative humidity (RH) when the RH was lower than 50%, whereas it decreased when the RH was higher than 50%.
Keywords: Sugars; BSOA; Formation; In-situ pH; Agricultural areas;
Relationships between the potential production of the greenhouse gases CO2, CH4 and N2O and soil concentrations of C, N and P across 26 paddy fields in southeastern China by Weiqi Wang; Jordi Sardans; Chun Wang; Congsheng Zeng; Chuan Tong; Dolores Asensio; Josep Peñuelas (458-467).
Paddy fields are a major global anthropogenic source of greenhouse gases. China has the second largest area under rice cultivation, so determining the relationships between the emission of greenhouse gases and soil carbon content, nutrient availabilities and concentrations and physical properties is crucial for minimizing the climatic impacts of rice agriculture. We examined soil nutrients and other properties, greenhouse-gas production and their relationships in 26 paddy fields throughout the province of Fujian in China, one of the most important provinces for rice production. High P and K concentrations, contents and availabilities were correlated with low rates of CO2 production, whereas high C and N contents were correlated with high rates of CH4 production. Mean annual precipitation (MAP) and rates of gas production were not clearly correlated, at least partly due to the management of flooding that can mask the effect of precipitation. Higher mean annual temperatures and soil Fe contents favored the production of N2O. C, N, P and K concentrations and their ratios, especially the C:K and N:K ratios, and P availability were correlated with CO2 and CH4 production across the province, with higher C:K and N:K ratios correlated positively with increased CO2 production and available P correlated negatively with CH4 production. A management strategy to avoid excessive C accumulation in the soil and to increase P availability and decrease available Fe contents would likely decrease the production of greenhouse gases.
Keywords: Paddy field; CH4 flux; N2O flux; Greenhouse gases; Elemental stoichiometry; Diurnal variation; Nitrogen; Soil nutrients; Phosphorus; Seasonal variation; Warming;
Compositional and surface characterization of HULIS by UV-Vis, FTIR, NMR and XPS: Wintertime study in Northern India by Varun Kumar; Anubha Goel; Prashant Rajput (468-475).
This study (first attempt) characterizes HULIS (Humic Like Substances) in wintertime aerosols (n = 12 during day and nighttime each) from Indo-Gangetic Plain (IGP, at Kanpur) by using various state-of-the art techniques such as UV-VIS, FTIR, 1H NMR and XPS. Based on UV-Vis analysis the absorption coefficient at 365 nm (babs-365) of HULIS was found to average at 13.6 and 28.8 Mm−1 during day and nighttime, respectively. Relatively high babs-365 of HULIS during the nighttime is attributed to influence of fog-processing. However, the power fit of UV-Vis spectrum provided near similar AAE (absorption Angstrom exponent) value of HULIS centering at 4.9 ± 1.4 and 5.1 ± 1.3 during daytime and nighttime, respectively. FTIR spectra and its double derivative revealed the presence of various functional groups viz. alcohols, ketones aldehydes, carboxylic acids as well as unsaturated and saturated carbon bonds. 1H NMR spectroscopy was applied to quantify relative percentage of various types of hydrogen atoms contained in HULIS, whereas XPS technique provided information on surface composition and oxidation states of various elements present. A significantly high abundance of H‒C‒O group has been observed in HULIS (based on 1H NMR); 41.4± 2.7% and 30.9± 2.4% in day and nighttime, respectively. However, aromatic protons (Ar-H) were higher in nighttime samples (19.3± 1.8%) as compared to that in daytime samples (7.5 ± 1.9). XPS studies revealed presence of various species on the surface of HULIS samples. Carbon existed in 7 different chemical states while total nitrogen and sulfur exhibited 3 and 2 different oxidation states (respectively) on the surface of HULIS. This study reports structural information and absorption properties of HULIS which has implications to their role as cloud condensation nuclei and atmospheric direct radiative forcing.Display Omitted
Keywords: HULIS; PM10; NMR; FTIR; XPS; UV-VIS; IGP;
Corrigendum to “Aerosol particle shrinkage event phenomenology in a South European suburban area during 2009–2015” [Atmos. Environ. 160C (2017) 154–164] by E. Alonso-Blanco; F.J. Gómez-Moreno; L. Núñez; M. Pujadas; M. Cusack; B. Artíñano (476).