Atmospheric Environment (v.153, #C)

Air quality simulations are performed to determine the impact of changes in future climate and emissions on regional air quality in the South Coast Air Basin (SoCAB) of California. The perturbation parameters considered in this study include (1) temperature, (2) absolute humidity, (3) biogenic VOC emissions due to temperature changes, and (4) boundary conditions. All parameters are first perturbed individually. In addition, the impact of simultaneously perturbing more than one parameter is analyzed. Air quality is simulated with meteorology representative of a summertime ozone pollution episode using both a baseline 2005 emissions inventory and a future emissions projection for the year 2023. Different locations within the modeling domain exhibit varying degrees of sensitivity to the perturbations considered. Afternoon domain wide average ozone concentrations are projected to increase by 13–18% as a result of changes in future climate and emissions. Afternoon increases at individual locations range from 10 to 36%. The change in afternoon particulate matter (PM) levels is a strong function of location in the basin, ranging from −7.1% to +4.7% when using 2005 emissions and −8.6% to +1.7% when using 2023 emissions. Afternoon secondary organic aerosol (SOA) concentrations for the entire domain are projected to decrease by over 15%, and the change in SOA levels is not a strong function of the emissions inventory utilized. Temperature increases play the dominant role in determining the overall impact on ozone, PM, and SOA concentrations in both the individual and combined perturbation scenarios.
Keywords: Air quality modeling; Ozone; Particulate matter; Secondary organic aerosols; South Coast Air Basin of California; Climate change;

The development and use of dispersion models that simulate traffic-related air pollution in urban areas has risen significantly in support of air pollution exposure research. In order to accurately estimate population exposure, it is important to generate concentration surfaces that take into account near-road concentrations as well as the transport of pollutants throughout an urban region. In this paper, an integrated modelling chain was developed to simulate ambient Nitrogen Dioxide (NO2) in a dense urban neighbourhood while taking into account traffic emissions, the regional background, and the transport of pollutants within the urban canopy. For this purpose, we developed a hybrid configuration including 1) a street canyon model, which simulates pollutant transfer along streets and intersections, taking into account the geometry of buildings and other obstacles, and 2) a Gaussian puff model, which resolves the transport of contaminants at the top of the urban canopy and accounts for regional meteorology. Each dispersion model was validated against measured concentrations and compared against the hybrid configuration. Our results demonstrate that the hybrid approach significantly improves the output of each model on its own. An underestimation appears clearly for the Gaussian model and street-canyon model compared to observed data. This is due to ignoring the building effect by the Gaussian model and undermining the contribution of other roads by the canyon model. The hybrid approach reduced the RMSE (of observed vs. predicted concentrations) by 16%–25% compared to each model on its own, and increased FAC2 (fraction of predictions within a factor of two of the observations) by 10%–34%.
Keywords: Dispersion modelling; Street canyon; Gaussian model; Hybrid model; SIRANE; CALPUFF; Traffic emissions;

Atmospheric nitrogen deposition to China: A model analysis on nitrogen budget and critical load exceedance by Yuanhong Zhao; Lin Zhang; Youfan Chen; Xuejun Liu; Wen Xu; Yuepeng Pan; Lei Duan (32-40).
We present a national-scale model analysis on the sources and processes of inorganic nitrogen deposition over China using the GEOS-Chem model at 1/2° × 1/3° horizontal resolution. Model results for 2008–2012 are evaluated with an ensemble of surface measurements of wet deposition flux and gaseous ammonia (NH3) concentration, and satellite measurements of tropospheric NO2 columns. Annual total inorganic nitrogen deposition fluxes are simulated to be generally less than 10 kg N ha−1 a−1 in western China (less than 2 kg N ha−1 a−1 over Tibet), 15–50 kg N ha−1 a−1 in eastern China, and 16.4 kg N ha−1 a−1 averaged over China. Annual total deposition to China is 16.4 Tg N, with 10.2 Tg N (62%) from reduced nitrogen (NHx) and 6.2 Tg N from oxidized nitrogen (NOy). Domestic anthropogenic sources contribute 86% of the total deposition; foreign anthropogenic sources 7% and natural sources 7%. Annually 23% of domestically emitted NH3 and 36% for NOx are exported outside the terrestrial land of China. We find that atmospheric nitrogen deposition is about half of the nitrogen input from fertilizer application (29.6 Tg N a−1), and is much higher than that from natural biological fixation (7.3 Tg N a−1) over China. A comparison of nitrogen deposition with critical load estimates for eutrophication indicates that about 15% of the land over China experiences critical load exceedances, demonstrating the necessity of nitrogen emission controls to avoid potential negative ecological effects.
Keywords: Nitrogen deposition; Nitrogen budget; Critical load; Ammonia; Nitrogen oxides;

Quantification of furandiones in ambient aerosol by Ibrahim M. Al-Naiema; Hannah M. Roppo; Elizabeth A. Stone (41-46).
Furandiones are products of the photooxidation of anthropogenic volatile organic compounds (VOC), like toluene, and contribute to secondary organic aerosol (SOA). Because few molecular tracers of anthropogenic SOA are used to assess this source in ambient aerosol, developing a quantification method for furandiones holds a great importance. In this study, we developed a direct and highly sensitive gas chromatography-mass spectrometry method for the quantitative analysis of furandiones in fine particulate matter that is mainly free from interference by structurally-related dicarboxylic acids. Our application of this method in Iowa City, IA provides the first ambient measurements of four furandiones: 2,5-furandione, 3-methyl-2,5-furandione, dihydro-2,5-furandione, and dihydro-3-methyl-2,5-furandione. Furandiones were detected in all collected samples with a daily average concentration of 9.1 ± 3.8 ng m−3. The developed method allows for the accurate measurement of the furandiones concentrations in ambient aerosol, which will support future evaluation of these compounds as tracers for anthropogenic SOA and assessment of their potential health impacts.Display Omitted
Keywords: Acid anhydride; Fine particulate matter; Anthropogenic VOC; Secondary organic aerosol; Method development; GCMS; Succinic anhydride; Methylsuccinic anyhydride; Maleic anyhdride; Citraconic anhydride;

Content, mineral allocation and leaching behavior of heavy metals in urban PM2.5 by Simona Mazziotti Tagliani; Monica Carnevale; Giovanna Armiento; Maria Rita Montereali; Elisa Nardi; Marco Inglessis; Fabrizio Sacco; Simonetta Palleschi; Barbara Rossi; Leopoldo Silvestroni; Antonio Gianfagna (47-60).
To clarify the relationship between airborne particulate exposure and negative impacts on human health, focusing on the heavy metal content alone might not be sufficient. To address this issue, in the present work, mineral allocation and leaching behavior of heavy metals in the PM2.5 were investigated. This work, therefore, provides a novel perspective in the field of urban airborne particle investigation that is not currently found in the literature. Four sampling campaigns were performed in the urban area of Rome (Central Italy) during the winter and summer seasons (February and July 2013 and 2014, respectively). The measured concentrations of the regulated elements of As, Cd, Ni and Pb were consistent with those reported by the local Environmental Agency (ARPA Lazio), but non-regulated heavy metals, including Fe, Cu, Cr and Zn, were also found in PM2.5 and analyzed in detail. As a novelty, heavy metals were associated with the host-identified mineral phases, primarily oxides and alloys, and to a lesser extent, other minerals, such as sulfates, carbonates and silicates. Leaching tests of the collected samples were conducted in a buffered solution mimicking the bodily physiological environment. Despite the highest concentration of heavy metals found during the winter sampling period, all of the elements showed a leaching trend leading to major mobility during the summer period. To explain this result, an interesting comparative analysis between the leaching test behavior and innovative mineral allocation was conducted. Both the heavy metal content and mineral allocation in PM2.5 might contribute to the bioavailability of toxic elements in the pulmonary environment. Hence, for regulatory purposes, the non-linear dependency of heavy metal bioavailability on the total metal content should be taken into account.
Keywords: PM2.5; Heavy metals; Bioavailability; Mineral allocation; Rome urban area;

Comparisons of methods to obtain insoluble particles in snow for transmission electron microscopy by Yong Ren; Xiongfei Zhang; Hailun Wei; Liang Xu; Jian Zhang; Jiaxing Sun; Xin Wang; Weijun Li (61-69).
Most studies of insoluble particles in snow have been focused on their mass concentration. Little is understood about the physicochemical properties of individual insoluble particles in snow. However, the information is essential to trace sources of the particles, to understand ice nuclei, and to quantify critical aerosol particles (e.g., black carbon) in snow analyzed by bulk methods. The lack of individual particle analyses of snow meltwater stems from the difficulty of producing feasible samples of the snow-borne insoluble particles. In this study, we examined six sample preparation methods and compared their results using transmission electron microscopy (TEM). The results are the following: (1) Drop-by-drop method (DDM) is the easiest method to make TEM samples but cannot remove the influence of the dissolved substances in snow meltwater. (2) Direct filtration method (DFM) was infeasible because the water penetration of carbon film on copper TEM grids is low. (3) Filtration and transfer method (FTM) is through using ultrasonication to transfer insoluble particles on the nuclepore polycarbonate membranes to TEM grids. The drawback of this method is that ultrasonication breaks individual particles into fragments. (4) Freeze-drying method (FDM) can result in new particles from the drying dissolved substances, which interferes with the identification of insoluble particles. (5) Dilution-gravity separation method (DGM) can obtain different substances based on their specific gravity in long standing water. The method can effectively reduce soluble substances but lose insoluble carbonaceous particles (e.g., soot and organic particles). (6) Tangential flow filtration and dilution (TFF-D) through concentrating and desalting dissolved substances is to remove the dissolved substances but keep insoluble particles in snow meltwater. The TFF-D method not only can be suitable for electron microscopy to study individual insoluble particles in snow meltwater but also for any offline microscopic observation such as Raman spectroscopy and mass spectrometry.
Keywords: Snow; Transmission electron microscopy; Tangential flow filtration and dilution; Ice nuclei;

Seasonal trends, chemical speciation and source apportionment of fine PM in Tehran by Mohammad Arhami; Vahid Hosseini; Maryam Zare Shahne; Mostafa Bigdeli; Alexandra Lai; James J. Schauer (70-82).
Frequent air pollution episodes have been reported for Tehran, Iran, mainly because of critically high levels of fine particulate matter (PM2.5). The composition and sources of these particles are poorly known, so this study aims to identify the major components and heavy metals in PM2.5 along with their seasonal trends and associated sources. 24-hour PM2.5 samples were collected at a main residential station every 6 days for a full year from February 2014 to February 2015. The samples were analyzed for ions, organic carbon (including water-soluble and insoluble portions), elemental carbon (EC), and all detectable elements. The dominant mass components, which were determined by means of chemical mass closure, were organic matter (35%), dust (25%), non-sea salt sulfate (11%), EC (9%), ammonium (5%), and nitrate (2%). Organic matter and EC together comprised 44% of fine PM on average (increased to >70% in the colder season), which reflects the significance of anthropogenic urban sources (i.e. vehicles). The contributions of different components varied considerably throughout the year, particularly the dust component that varied from 7% in the cold season to 56% in the hot and dry season. Principal component analyses were applied, resulting in 5 major source factors that explained 85% of the variance in fine PM. Factor 1, representing soil dust, explained 53%; Factor 2 denotes heavy metals mainly found in industrial sources and accounted for 18%; and rest of factors, mainly representing combustion sources, explained 14% of the variation. The levels of major heavy metals were further evaluated, and their trends showed considerable increases during cold seasons. The results of this study provide useful insight to fine PM in Tehran, which could help in identifying their health effects and sources, and also adopting effective control strategies.Display Omitted
Keywords: PM2.5; Toxic metals; Dust; PCA; CMC; Tehran;

Effect of spatial outliers on the regression modelling of air pollutant concentrations: A case study in Japan by Shin Araki; Hikari Shimadera; Kouhei Yamamoto; Akira Kondo (83-93).
Land use regression (LUR) or regression kriging have been widely used to estimate spatial distribution of air pollutants especially in health studies. The quality of observations is crucial to these methods because they are completely dependent on observations. When monitoring data contain biases or uncertainties, estimated map will not be reliable. In this study, we apply the spatial outlier detection method, which is widely used in soil science, to observations of PM2.5 and NO2 obtained from the regulatory monitoring network in Japan. The spatial distributions of annual means are modelled both by LUR and regression kriging using the data sets with and without the detected outliers respectively and the obtained results are compared to examine the effect of spatial outliers. Spatial outliers remarkably deteriorate the prediction accuracy except for that of LUR model for NO2. This discrepancy of the effect might be due to the difference in the characteristics of PM2.5 and NO2. The difference in the number of observations makes a limited contribution to it. Although further investigation at different spatial scales is required, our study demonstrated that the spatial outlier detection method is an effective procedure for air pollutant data and should be applied to it when observation based prediction methods are used to generate concentration maps.
Keywords: Land use regression; Variogram; Kriging; PM2.5; NO2;

Numerical air quality forecasting over eastern China: An operational application of WRF-Chem by Guangqiang Zhou; Jianming Xu; Ying Xie; Luyu Chang; Wei Gao; Yixuan Gu; Ji Zhou (94-108).
The Regional Atmospheric Environmental Modeling System for eastern China (RAEMS) is an operational numerical system to forecast near surface atmospheric pollutants such as PM2.5 and O3 over the eastern China region. This system was based on the fully online coupled weather research and forecasting/chemistry (WRF-Chem) model. Anthropogenic emissions were based on the multi-resolution emission inventory for China (MEIC), and biogenic emissions were online calculated using model of emissions of gases and aerosols from nature (MEGAN2). Authorized by the China Meteorological Administration (CMA), this system started to provide operational forecast in 2013. With a large domain covering eastern China, the system produces daily 72-hr forecast. In this work, a comprehensive evaluation was carried out against measurements for two full years (2014–2015). Evaluation results show that the RAEMS is skillful in forecasting temporal variation and spatial distribution of major air pollutants over the eastern China region. The performance is consistent in different forecast length of 24 h, 48 h, and 72 h. About half of cities have correlation coefficients greater than 0.6 for PM2.5 and 0.7 for daily maximum 8-h averaged (DM8H) ozone. The forecasted PM2.5 is generally in good agreement with observed concentrations, with most cities having normalized mean biases (NMB) within ±25%. Forecasted ozone diurnal variation is very similar to that of observed, and makes small peak time error for DM8H ozone. It also shows good capability in capturing ozone pollution as indicated by high critical success indexes (CSI). The modeling system also exhibits acceptable performance for PM10, NO2, SO2, and CO. Meanwhile, degraded performance for PM2.5 is found under heavy polluted conditions, and there is a general over estimation in ozone concentrations.
Keywords: Air quality modeling; Air quality forecasting; WRF-Chem; PM2.5; Ozone;

Letter to the editor: Critical assessments of the current state of scientific knowledge, terminology, and research needs concerning the ecological effects of elevated atmospheric nitrogen deposition in China by Yuepeng Pan; Yongwen Liu; Gregory R. Wentworth; Lin Zhang; Yuanhong Zhao; Yi Li; Xuejun Liu; Enzai Du; Yunting Fang; Hongwei Xiao; Hongyuan Ma; Yuesi Wang (109-116).
Keywords: Nitrogen deposition; Bulk deposition; Wet deposition; Dry deposition; China;

Gaseous mercury flux from salt marshes is mediated by solar radiation and temperature by Tom Sizmur; Gordon McArthur; David Risk; Robert Tordon; Nelson J. O'Driscoll (117-125).
Salt marshes are ecologically sensitive ecosystems where mercury (Hg) methylation and biomagnification can occur. Understanding the mechanisms controlling gaseous Hg flux from salt marshes is important to predict the retention of Hg in coastal wetlands and project the impact of environmental change on the global Hg cycle. We monitored Hg flux from a remote salt marsh over 9 days which included three cloudless days and a 4 mm rainfall event. We observed a cyclical diel relationship between Hg flux and solar radiation. When measurements at the same irradiance intensity are considered, Hg flux was greater in the evening when the sediment was warm than in the morning when the sediment was cool. This is evidence to suggest that both solar radiation and sediment temperature directly influence the rate of Hg(II) photoreduction in salt marshes. Hg flux could be predicted from solar radiation and sediment temperature in sub-datasets collected during cloudless days (R2 = 0.99), and before (R2 = 0.97) and after (R2 = 0.95) the rainfall event, but the combined dataset could not account for the lower Hg flux after the rainfall event that is in contrast to greater Hg flux observed from soils after rainfall events.
Keywords: Mercury; Salt marsh; Wetland; Sediment; Dynamic flux chamber;

Air pollutants and toxic emissions of various mileage motorcycles for ECE driving cycles by Jiun-Horng Tsai; Pei-Hsiu Huang; Hung-Lung Chiang (126-134).
Motorcycles were selected to determine their fuel consumption and exhaust emissions following ECE driving cycles. Exhaust constituents including CO2, CO, NOx, total hydrocarbons (THC) and hydrocarbon species (27 paraffins, 9 olefins, 16 aromatics and 15 carbonyls) were investigated for this work. The age of 10– 90% of the selected motorcycles ranged from 2.5 to 12.4 years, and their mileage ranged from 5400 to 39,300 km. CO emission ranged from 1.4 to 6.4 g/km (median value: 2.98 g/km), THC from 0.41 to 1.54 g/km (median value: 0.98 g/km), NOx from 0.16 to 0.28 g/km (median value: 0.21 g/km), CO2 from 58.9 to 62.2 g/km (median value: 60.5 g/km) and fuel consumption from 30.7 to 36.4 km/L (median value: 33.4 km/L), corresponding to the percentage cumulative data from 10 to 90% of the selected motorcycles. Results indicated that the motorcycle exhaust emission and fuel consumption depended on their mileage and ages. An increase in mileage of 1000 km resulted in an increase of 103 mg for CO emission and 14.7 mg for hydrocarbon emission and a reduction of 1.52 mg NOx emission and 0.11 km per liter fuel consumption. For various VOC groups, a mileage increase of 1000 km corresponding to the increased exhaust emission of paraffins was 6.71 mg, olefins 1.90 mg, aromatics 7.04 mg, carbonyls 0.283 mg and 67 VOC species 15.9 mg. Fuel consumption and emissions of CO and hydrocarbon increased in motorcycles over the guaranteed mileage of 15,000 km.
Keywords: Volatile organic compounds (VOCs); Mileage; Four-stroke motorcycle;

Growing season methane emissions from a permafrost peatland of northeast China: Observations using open-path eddy covariance method by Xueyang Yu; Changchun Song; Li Sun; Xianwei Wang; Fuxi Shi; Qian Cui; Wenwen Tan (135-149).
The mid-high latitude permafrost peatlands in the Northern Hemisphere is a major natural source of methane (CH4) to the atmosphere. Ecosystem scale CH4 emissions from a typical permafrost peatland in the Great Hing'an Mountains were observed during the growing season of 2014 and 2015 using the open-path eddy covariance method. Relevant environmental factors such as temperature and precipitation were also collected. There was a clear diurnal variation in methane emissions in the second half of each growing season, with significantly higher emission rates in the wet sector of study area. The daily CH4 exchange ranged from 1.8 mg CH4 m−2 d−1 to 40.2 mg CH4 m−2 d−1 in 2014 and ranged from −3.9 to 15.0 mg CH4 m−2 d−1 in 2015. There were no peaks of CH4 fluxes during the spring thawing period. However, large peaks of CH4 emission were found in the second half of both growing seasons. The CH4 emission after Jul 25th accounted for 77.9% of total growing season emission in 2014 and 85.9% in 2015. The total CH4 emission during the growing season of 2014 and 2015 was approximately 1.52 g CH4 m−2 and 0.71 g CH4 m−2, respectively. CH4 fluxes during the growing seasons were significantly correlated with thawing depth (R 2  = 0.71, P < 0.01) and soil temperatures (R 2  = 0.75, P < 0.01) at 40 cm depth. An empirical equation using these two major variables was modified to estimate growing season CH4 emissions in permafrost peatlands. Our multiyear observations indicate that the time-lagged volume of precipitation during the growing season is a key factor in interpreting locally inter-annual variations in CH4 emissions. Our results suggested that the low temperature in the deep soil layers effectively restricts methane production and emission rates; these conditions may create significant positive feedback under global climate change.
Keywords: Permafrost peatlands; Methane emission; Micrometeorological measurement; Influencing factors; Eddy covariance;

MODIS 3 km and 10 km aerosol optical depth for China: Evaluation and comparison by Qingqing He; Ming Zhang; Bo Huang; Xuelian Tong (150-162).
The recently released Moderate Resolution Imaging Spectrometer (MODIS) Collection 6 introduced a fine scale aerosol optical depth (AOD) distribution, the 3 km product, which is expected to perform well in analyzing aerosols and identifying local air pollution, especially in the severely polluted atmosphere of China. However, few detailed evaluations of regional variations have been conducted. In this paper, we evaluate MODIS 3 km and 10 km AOD products for China against ground-based measurements and compare their performance with respect to spatial and temporal variations. The ground validations indicate that the two products are generally correlated well to ground-based observations. Spatially, the 3 km product slightly outperform the 10 km product in well-developed areas of southern China. Temporally, both products perform worse during spring and summer. Atmospheric clouds and underlying surface are two key factors that influence the accuracy and number of retrievals for both products. The comparison analysis reveals the newly introduced AOD product clearly shows good relationships with the coarse resolution retrievals in spatial and temporal variation but significant differences regarding details. The 3 km AOD product provides better aerosol gradients, more retrievals in bare areas of western China and some spikes of diurnal variation in cloudy days. Seasonal comparisons show the 3 km AOD product is higher than the 10 km product in all seasons, especially during spring and summer. Although the 3 km product for China generally performs slightly worse than the 10 km product, the added information of the MODIS 3 km AOD product shows potential for studying local aerosol characterization, and may facilitate studies of air pollution.
Keywords: MODIS; AERONET; Aerosol optical depth; Validation; Spatiotemporal comparison; China;

Evaluation of summertime surface ozone in Kanto area of Japan using a semi-regional model and observation by Tran Thi Ngoc Trieu; Daisuke Goto; Hisashi Yashiro; Ryo Murata; Kengo Sudo; Hirofumi Tomita; Masaki Satoh; Teruyuki Nakajima (163-181).
Surface ozone is an air pollutant and harmful to human life. The spatial distribution of the air pollution has been estimated by chemical transport models, but still there are large uncertainties depending on detailed condition of the region. In this study, we extended Goto et al. (2015a) for implementing a chemical transport model to simulate short-lived gases such as ozone over Kanto area (around Tokyo in Japan) for August 2010. Comparison of simulation results with observed data indicated that the model had ability to capture observed ozone diurnal cycles over the target region with high correlation coefficients (0.69–0.81). The simulation result showed a vital role of meteorological conditions in the model performance. The correlation coefficients were much higher (0.78–0.87) and biases were lower (<35%) when the meteorological conditions were stable. In contrast, dominance of local pressure system and an associated complex wind field were main reasons for overestimated surface ozone concentrations in the unstable weather conditions.This study helped achieve a better understanding of the chemistry transport model performance under unstable meteorological conditions in the Kanto area. Maximal association between meteorological factors and surface ozone distribution was revealed. In addition, uncertainty of emission inventories of ozone precursors especially the underestimate NOx level certainly contributed to high level surface ozone during nighttime in this study.
Keywords: Stretch NICAM; Emission inventories; Surface ozone; Chemical transport model; Overestimated;

Effects of climate change, CO2 and O3 on wheat productivity in Eastern China, singly and in combination by Fulu Tao; Zhaozhong Feng; Haoye Tang; Yi Chen; Kazuhiko Kobayashi (182-193).
Air pollution and climate change are increasing threats to agricultural production and food security. Extensive studies have focused on the effect of climate change, but the interactive effects of multiple global change factors are poorly understood. Here, we incorporate the interactions between climate change, carbon dioxide (CO2) and ozone (O3) into an eco-physiological mechanistic model based on three years of O3 Free-Air Concentration Elevation (O3-FACE) experiments. We then investigate the effects of climate change, elevated CO2 concentration ([CO2]) and rising O3 concentration ([O3]) on wheat growth and productivity in eastern China in 1996–2005 (2000s) and 2016–2025 (2020s) under two climate change scenarios, singly and in combination. We find the interactive effects of climate change, CO2 and O3 on wheat productivity have spatially explicit patterns; the effect of climate change dominates the general pattern, which is however subject to the large uncertainties of climate change scenarios. Wheat productivity is estimated to increase by 2.8–9.0% due to elevated [CO2] however decline by 2.8–11.7% due to rising [O3] in the 2020s, relative to the 2000s. The combined effects of CO2 and O3 are less than that of O3 only, on average by 4.6–5.2%, however with O3 damage outweighing CO2 benefit in most of the region. This study demonstrates a more biologically meaningful and appropriate approach for assessing the interactive effects of climate change, CO2 and O3 on crop growth and productivity. Our findings promote the understanding on the interactive effects of multiple global change factors across contrasting climate conditions, cast doubt on the potential of CO2 fertilization effect in offsetting possible negative effect of climate change on crop productivity as suggested by many previous studies.Display Omitted
Keywords: Air pollution; Climate change; CO2 fertilization; Crop; Ozone; Risk;

Aerosol size distribution and new particle formation events in the suburb of Xi'an, northwest China by Yan Peng; Xiaodong Liu; Jin Dai; Zhao Wang; Zipeng Dong; Yan Dong; Chuang Chen; Xingmin Li; Na Zhao; Chao Fan (194-205).
Particle number concentration and size distribution are important for better understanding the characteristics of aerosols. However, their measurements are scarce in western China. Based on the first measurement of particle number size distribution (10–487 nm) in the suburb of Xi'an, northwest China from November 2013 to December 2014, the seasonal, monthly and diurnal average particle number concentrations were investigated, and the characteristics of new particle formation (NPF) events and their dependencies on meteorological parameters also discussed. The results showed that the annual average particle number concentrations in the nucleation (NNUC), Aitken (NAIT), and Accumulation (NACC) size ranges were 960 cm−3, 4457 cm−3, 3548 cm−3, respectively. The mean total particle number concentration (NTOT) was 8965 cm−3 and largely dominated by particles in Aitken mode. The number concentration was dominated by particles around 67.3 nm in spring, summer and fall, while about 89.8 nm in winter. The percentage of the ultrafine size range (UFP, particles of diameter below 100 nm) to total particle number concentration was 63.2%, 69.6%, 62.2% and 58.1% in four seasons. The diurnal variation of the nucleation mode particles was mainly influenced by NPF events in summer, while by both traffic densities and NPF events in spring, fall and winter. The diurnal variation of the number concentration of Aitken mode particles correlated with the traffic emission in spring, fall and winter, while in summer it more correlated with contribution of the growth of the nucleation mode particles. The burst of nucleation mode particles typically started in the daytime (08:15–16:05, LST). The growth rates of nucleated particles ranged from 2.8 to 10.7 nm h-1 with an average of 5.0 ± 1.9 nm h-1. Among observed 66 NPF events from 347 effective measurement days, 85 percent of their air masses came from north or northwest China, resulting in a low concentration of pre-existing particles, and only 15 percent came southerly from Qingling Mountains. Based on their growth rate, 64 and 36 percent of their subsequent particles, corresponding to types 1 and 2 NPF events, grew and seldom grew after the burst of nucleation mode particles. For type 1 NPF event, the nucleated particles could grow up to 40 nm or larger when surface winds shifted from westerly to easterly or southeasterly (from village areas). For type 2 NPF events, the particles kept almost unchanged when the winds stayed westerly. This implied that the surface wind direction with different emissions might play an important role in new particle growth in suburb of Xi'an.
Keywords: Atmospheric aerosol; Size distribution; New particle formation; Meteorological parameters;

Stable hydrogen isotope composition of n-alkanes in urban atmospheric aerosols in Taiyuan, China by Huiling Bai; Yinghui Li; Lin Peng; Xiangkai Liu; Xiaofeng Liu; Chongfang Song; Ling Mu (206-216).
The hydrogen isotope compositions (δD) of n-alkanes associated with particulate matter with a diameter of ≤10 μm from Taiyuan, China, during heating and non-heating periods were measured via gas chromatography–isotope ratio mass spectrometry to reveal the spatial and temporal characteristics of five functional zones and to provide another constraint on atmospheric pollutants. The δD values of n-C16 to n-C31 during the heating and non-heating periods ranged from −235.9‰ to −119.8‰ and from −231.3‰ to −129.2‰, respectively, but these similar spans had different distribution features. During the heating period, the δD distributions between non–central heating and commercial districts were consistent, as were those between residential and industrial districts; the n-alkanes came from two or more types of emission sources. Coal soot might be the primary local emission source, but not the only source. During the non-heating period, the n-alkanes of n-C16 to n-C20 were more depleted in D with the increasing carbon number in all functional zones, but there was no rule for n-C21 to n-C31. Specifically, coal soot and vehicle exhaust might be the primary sources of n-alkanes for non–central heating districts in the heating and non-heating periods, respectively, according to the δD distribution of n-C18 to n-C22; gasoline vehicle exhaust might be an n-alkane source, and the hydrogen isotope fractionation effect during the condensation process should be a pollution mechanism for the commercial district during the heating period; the δD distribution difference of n-C16 to n-C18 between the two periods in the residential and industrial districts was consistent, which indicates a similar source of fossil fuel combustion and a similar isotope fractionation effect during the non-heating period.
Keywords: n-alkanes; Hydrogen isotope composition; PM10; Atmospheric aerosol;

Hygroscopic properties of urban aerosols and their cloud condensation nuclei activities measured in Seoul during the MAPS-Seoul campaign by Najin Kim; Minsu Park; Seong Soo Yum; Jong Sung Park; In Ho Song; Hye Jung Shin; Joon Young Ahn; Kyung-Hwan Kwak; Hwajin Kim; Gwi-Nam Bae; Gangwoong Lee (217-232).
Aerosol physical properties, chemical compositions, hygroscopicity and cloud condensation nuclei (CCN) activities were measured in Seoul, the highly populated capital city of Korea, during the Megacity Air Pollution Studies (MAPS-Seoul) campaign, in May–June 2015. The average aerosol concentration for particle diameters >10 nm was 11787 ± 7421 cm−3 with dominant peaks at morning rush hours and in the afternoon due to frequent new particle formation (NPF) events. The average CCN concentration was 4075 ± 1812 cm−3 at 0.6% supersaturation, with little diurnal variation. The average hygroscopicity parameter ( κ ) value determined using a humidified tandem differential mobility analyzer (HTDMA) ranged 0.17–0.27 for a range of particle diameters (30–150 nm). The κ values derived using the aerosol mass spectrometer (AMS) data with three different methods were 0.32–0.34, significantly higher than those from HTDMA due to the uncertainties in the hygroscopicity values of different chemical compositions, especially organics and black carbon. Factors affecting the aerosol hygroscopicity seemed to be traffic and chemical processes during the NPF events. The CCN concentration predicted based on HTDMA κ data showed very good agreement with the measured one. Because of the overestimation of κ , CCN closure with the predicted CCN concentration based on AMS κ data over-predicted CCN concentration although the linear correlation between measured and predicted CCN concentration was still very good.
Keywords: Aerosol hygroscopicity; Urban aerosol; Cloud condensation nuclei activity; Ground measurement; MAPS-Seoul;

In a recent publication of Atmospheric Environment, Huang et al. (2016) reported nitrogen (N) deposition estimates using the water surrogate surface method. This method may be suitable to evaluate the atmospheric N input to a body of water, wetland or paddy fields rather than dry crop land without sustained waterlogged conditions. Such a method may also result in the potential underestimation of both dry and wet N deposition due to the release of ammonia (NH3) from water evaporation and/or N loss from biological activities, and hence bias the relative contribution of dry deposition to total deposition. Besides the uncertainties regarding the magnitude and pathways of N deposition, the statement by Huang et al. (2016) that “nitrate was the dominant species in N deposition even in cropland” is also questionable. We suggest that reduced species dominate the N deposition in Huang-Huai-Hai Plain (i.e., North China Plain) even in urban and industrial regions due to the abundance of NH3.
Keywords: Nitrogen deposition; Ammonia; Wet deposition; Dry deposition; North China Plain;

Response to discussion of “Atmospheric deposition as an important nitrogen load to a typical agro-ecosystem in the Huang-Huai-Hai Plain” by Huang et al. (2016) by Ping Huang; Jiabao Zhang; Donghao Ma; Zhaofei Wen; Shengjun Wu; Gina Garland; Engil Isadora Pujol Pereira; Anning Zhu; Xiuli Xin; Congzhi Zhang (236-239).