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Understanding the compositions and evolution of atmospheric organic vapors is crucial for exploring their impact on air quality. However, the molecular and seasonal characteristics of organic vapors in urban areas, with complex anthropogenic emissions and high variability, remain inadequately understood. In this study, we conducted measurements in urban Beijing during 2021-2022 covering four seasons using a Vocus-PTR, an improved Proton Transfer Reaction-Mass Spectrometry (PTR-MS). During the measurement period, a total of 895 peaks are observed, and 543 of them can be assigned to formulas. The contribution of CxHyOz species is most significant, which compose up to 53.7% of the number and 76.0% of the mass of total organics. With enhanced sensitivity and mass resolution, various sub-ppt level species and organics with multiple oxygens (≥3) were discovered. When counting the species number, 42.2% of the organics measured are at sub-ppt level and 37.8% of the species contain 3-8 oxygens. Organic vapors with multiple oxygens mainly consist of intermediate volatility and semi-volatile compounds, and many of them are found to be the multi-generational oxidation products of various volatile organic precursors. In summer, the fast photooxidation process generates organic vapors with multiple oxygens, and leads to an increase in both their concentration and proportion. While in other seasons, the variations of organic vapors with multiple oxygens are closely correlated with those of organic vapors with 1-2 oxygens, which could be heavily influenced by primary emissions. Organic vapors with low oxygen content (≤ 2 oxygens) are comparable to the results obtained by traditional PTR-MS measurements in both urban Beijing and neighboring regions. [ABSTRACT FROM AUTHOR]

Vehicle emissions have become a major source of air pollution in urban areas, especially for near-road environments, where the pollution characteristics are difficult to be captured by a single-scale air quality model due to the complex composition of the underlying surface. Here we developed a hybrid model CMAQ-RLINE_URBAN to quantitatively analyse the effects of vehicle emissions on urban roadside NO2 concentrations at a high spatial resolution of 50 m × 50 m. To estimate the influence of various street canyons on the dispersion of air pollutants, a Machine Learning-based Street Canyon Flow (MLSCF) scheme was constructed based on Computational Fluid Dynamic and ensemble learning methods. The results indicated that compared with the CMAQ model, the hybrid model improved the underestimation of NO2 concentration at near-road sites with MB changing from -10 µg/m³ to 6.3 µg/m³. The MLSCF scheme obviously increased concentrations at upwind receptors within deep street canyons due to changes in the wind environment caused by the vortex. In summer, the relative contribution of vehicles to NO2 concentrations in Beijing urban areas was 39 % on average, similar to results from CMAQ-ISAM model, but increased significantly with the decreased distance to the road centerline, especially reaching 75 % on urban freeways. [ABSTRACT FROM AUTHOR]

Understanding carbon sources and sinks across the Earth's surface is fundamental in climate science and policy; thus, these topics have been extensively studied but have yet to be fully resolved and are associated with massive debate regarding the sign and magnitude of the carbon budget from global to regional scales. Developing new models and estimates based on state-of-the-art algorithms and data constraints can provide valuable knowledge and contribute to a final ensemble model in which various optimal carbon budget estimates are integrated, such as the annual Global Carbon Budget paper. Here, we develop a new atmospheric inversion system based on the four-dimensional local ensemble transform Kalman filter (4D-LETKF) coupled with the GEOS-Chem global transport model to infer surface-to-atmosphere net carbon fluxes from Orbiting Carbon Observatory-2 (OCO-2) V10r XCO2 retrievals. The 4D-LETKF algorithm is adapted to an OCO-2-based global carbon inversion system for the first time in this work. On average, the mean annual terrestrial and oceanic fluxes between 2015 and 2020 are estimated as -2.02 GtC yr-1 and -2.34 GtC yr-1, respectively, compensating for 21 % and 24 %, respectively, of global fossil CO2 emissions (9.80 GtC yr-1). Our inversion results agree with the CO2 atmospheric growth rates reported by the National Oceanic and Atmospheric Administration (NOAA) and reduce the modelled CO2 concentration biases relative to the prior fluxes against surface and aircraft measurements. Our inversion-based carbon fluxes are broadly consistent with those provided by other global atmospheric inversion models, although discrepancies still occur in the land-ocean flux partitioning schemes and seasonal flux amplitudes over boreal and tropical regions, possibly due to the sparse observational constraints of the OCO-2 satellite and the divergent prior fluxes used in different inversion models. Four sensitivity experiments are performed herein to vary the prior fluxes and uncertainties in our inversion system, suggesting that regions that lack OCO-2 coverage are sensitive to the priors, especially over the tropics and high latitudes. In the further development of our inversion system, we will optimize the data-assimilation configuration to fully utilize current observations and increase the spatial and seasonal representativeness of the prior fluxes over regions that lack observations. [ABSTRACT FROM AUTHOR]

Ship emissions and coastal air pollutions around China are expected to be alleviated with the gradually implemented of domestic ship emission control (DECA) policy. However, there is so far a lack of a comprehensive post assessment on the ship emission response after the policy implementation. This study developed a series of high spatiotemporal ship emission inventories of China's inland rivers and the 200 Nm zone from 2016 to 2019 based on an updated Ship Emission Inventory Model (SEIM v2.0) and analysed the interannual changes of emissions under the influence of both ship activity increase and gradually promoted policy. The route restoration technology in SEIM v2.0 has greatly improved the spatial distribution of ship emissions and the river vessels (RVs) are better distinguished by using the spatial frequency distribution method. From 2016 to 2019, SO2 and PM emissions from ships decreased by 29.6 % and 26.4 %, respectively, while ship NOX emissions increased by 13.0 %. Although the DECA 1.0 policy has been implemented since 2017, it was not until 2019 with the DECA 2.0 that significant emission reduction was achieved, e.g., 33.3 % regarding SO2. Considering the potential emissions brought by continuous growth of maritime trade, however, an even larger emission reduction effect of 39.8 % was achieved in 2019 compared with the scenario without switching cleaner fuel. Although ocean-going vessels (OGVs) contributed to approximately 2/3 of ship emissions in Chinese waters, 2/3 of them came from ships registered in other countries. Containers and bulk carriers are still the dominate contributors to ship emissions, and newly- built, large ships and ships using clean fuel oil are taking an increasingly large proportion in emission structure. The four-year consecutive daily ship emissions were presented for major ports, which timely reflects the response of step-by-step DECA policy on emissions and may provide useful references for port observation experiments and local policy making. In addition, the spatial distribution shows that a number of ships detoured outside the scope of DECA 2.0 in 2019 to save the cost on more expensive low sulphur oil, increasing emissions in farther maritime areas. The multi-year ship emission inventory provide high-quality datasets for air quality and dispersion modellings, as well as verifications for in-situ observation experiments, which may also guide further ship emission control direction in China. [ABSTRACT FROM AUTHOR]

Hydroxymethanesulfonate (HMS) has recently been identified as an abundant organosulfur compound in aerosols during winter haze episodes in northern China. It has also been detected in other regions, although the concentrations are low. Because of the sparse field measurements, the global significance of HMS and its spatial and seasonal patterns remain unclear. Here, we implement HMS chemistry into the GEOS-Chem chemical transport model and conduct multiple global simulations. The developed model accounts for cloud entrainment and gas-aqueous mass transfer within the rate expressions for heterogeneous sulfur chemistry. Our simulations can generally reproduce the available HMS observations, and show that East Asia has the highest HMS concentration, followed by Europe and North America. The simulated HMS shows a seasonal pattern with higher values in the colder period. Photochemical oxidizing capacity affects the competition of formaldehyde with oxidants (such as ozone and hydrogen peroxide) for sulfur dioxide and is a key factor influencing the seasonality of HMS. The highest average HMS concentration (1-3 μg m-3) and HMS/sulfate molar ratio (0.1-0.2) are found in northern China winter. The simulations suggest that aqueous clouds act as the major medium for HMS chemistry while aerosol liquid water may play a role if its rate constant for HMS formation is greatly enhanced compared to cloud water. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) are essential in secondary organic aerosol (SOA) formation due to their dual roles as precursors and oxidant producers. In this work, the VOC species in Xinxiang, a mid-sized city located in Henan Province in central China, were measured and analysed from November 5th to December 3rd, 2018. Based on online monitoring with proton transfer reaction-mass spectrometry (PTR-MS) and canister grab samples, 53 VOC species are obviously detected, and the most abundant categories are oxygenated VOCs (OVOCs) and benzenoids. Compared with field measurements in other regions, the mixing ratios of BTEX (benzene, toluene, ethylbenzene, and xylene), acetaldehyde, and C3 carbonyls are at high levels, indicating intensive anthropogenic emissions in Xinxiang. According to the positive matrix factorization (PMF) model, benzenoids are mainly emitted from solvent evaporation (~47 %), residential heating (~19 %), industrial emission (~16 %), and vehicle exhaust (~10 %), while the contributions from biogenic and secondary sources as well as thermal power generation are minor. However, the emissions of total OVOCs from the six resolved sources are similar. The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) results show that the transport contribution for VOCs is not intensive, but the cities within Henan Province or in the neighbouring provinces may influence the mixing ratios to some extent. The roles of benzenoids and OVOCs in SOA formation are investigated by estimating the mass of oxidation products and rates of OH radical production. Among the observed VOCs, toluene has the largest SOA formation potential (SOAFP), while its weight in SOA formation declines with the aggravation of pollution. On the other hand, the SOA concentration shows a good relationship with OH exposure, which highlights the importance of the atmospheric oxidation capacity, especially in polluted periods. Formaldehyde is the strongest radical contributor, and the contribution of acetaldehyde is also significant in this study. Furthermore, solvent evaporation, industrial emissions, and vehicle exhaust are estimated as the top three anthropogenic contributors with the highest SOAFP and radical contribution rate. [ABSTRACT FROM AUTHOR]

Severe winter hazes accompanied by high concentrations of fine particulate matter (PM2.5) occur frequently in the North China Plain and threaten public health. Organic matter (OM) and sulfate are recognized as major components of PM2.5, while atmospheric models often fail to predict their high concentrations during severe winter hazes due to incomplete understanding of secondary aerosol formation mechanisms. By using a novel combination of single particle mass spectrometer and optimized ion chromatography measurement, here we show that hydroxymethanesulfonate (HMS), formed by the reaction between formaldehyde (HCHO) and dissolved SO2 in aerosol water, is ubiquitous in Beijing winter. The HMS concentration and the molar ratio of HMS to sulfate increased with the deterioration of winter haze. High concentrations of precursors (SO2 and HCHO) coupled with low oxidant levels, low temperature, high relative humidity, and moderately acid pH facilitate the heterogeneous formation of HMS, which could account for up to 15 % of OM in winter haze and lead to 36 % overestimates of sulfate when using traditional ion chromatography measurements. Despite the clean air actions have substantially reduced SO2 emissions, HMS concentration and molar ratio of HMS to sulfate during severe winter hazes increased from 2015 to 2016 with the growth of HCHO concentration. Our findings illustrate the significant contribution of heterogeneous HMS chemistry to severe winter hazes in Beijing, which help to improve the prediction of OM and sulfate, and suggest that the reduction in HCHO can help to mitigate haze pollution. [ABSTRACT FROM AUTHOR]

Two parallel field studies were conducted simultaneously at both urban and rural sites in Beijing from 11/01/2016 to 11/29/2016. Online single-particle chemical composition analysis was used as a tracer system to investigate the impact of heating activities and the formation of haze events. Central heating elevated EC-Nit, EC-Nit-Sul, and ECOC-Nit levels by 1.5–2.0 times due to the increased use of coal in the urban areas. However, in the rural areas, residential heating which mainly consumes low-quality coal and biomass burning elevated ECOC-Nit-Sul, Nak-Nit, and OC-Sul levels by 1.2–1.5 times. Four severe haze events (hourly PM2.5 > 200 µg m−3) occurred at both sites during the studies. In each event, a pattern of transport and accumulation was found. In the first stage, particles were regionally transported from the south or southwest and accumulated under air stagnations, creating the significant secondary formation. Consequently, the boosting of PM2.5 led to severe haze. At both sites, the severe haze occurred due to different patterns of local emission, transport, and secondary processes. At PG, the sulfate-rich residential coal burning particles were dominant. The regional transport between PG and PKU was simulated using the WRF-HYSPLIT model, confirming that the transport from PG to PKU was significant, but PKU to PG occurred occasionally. These cases can explain the serious air pollution in the urban areas of Beijing and the interaction between urban and rural areas. This study can provide references for enhancing our understanding of haze formation in Beijing. [ABSTRACT FROM AUTHOR]

Two single particle aerosol mass spectrometers (SPAMS) were deployed simultaneously at an urban and a rural site in Beijing during an intensive field campaign from 1st to 29th Nov 2016 to investigate the source and process of airborne particles in Beijing. In the first part of this research, we report the single-particle chemical composition, mixing state, and evolution at both sites. 96 % and 98 % of collected particles were carbonaceous at the urban and rural sites, respectively. Five particle categories, including elemental carbon (EC), organic carbon (OC), internal-mixed EC and OC (ECOC), potassium-rich (K-rich), and Metals were observed at both sites. The categories were partitioned into particle types depending on different atmospheric processing stages. Seventeen particle types were shared at both sites. In the urban area, nitrate-containing particle types, such as EC-Nit and ECOC-Nit, were enriched, especially at night; sulfate-containing particles were transported when wind speed was high; ECOC-Nit-Sul were mostly local-aged. In sum, these processed particles took up to 85.3 % in the urban areas. In the rural area, regional particles were abundant, but freshly emitted ECOC and OC had distinct patterns that were pronounced at cooking and heating time. Biomass burning, traffic, and coal burning were major sources of PM2.5 in both rural and urban areas. Besides, the particles from the steel industry located in the south were also identified. In summary, the chemical composition of urban and rural particle types was similar in Beijing; the urban particles were influenced significantly by rural processing and transport. The work is useful to understand the evolution of urban and rural particles in Beijing during winter. [ABSTRACT FROM AUTHOR]

Air quality in China has changed dramatically in response to rapid development of economy and policies. In this work, we investigate the changes of anthropogenic source contribution to ambient fine particulate matter (PM2.5) air pollution and related health impacts in China during 1990-2015 and elucidate the drivers behind the decadal transition. We estimate the contribution of five anthropogenic emitting sectors to ambient PM2.5 exposure and related premature mortality over China during 1990-2015 with 5-yr intervals, by using an integrated model framework of bottom-up emission inventory, chemical transport model, and the Global Exposure Mortality Model (GEMM). The national anthropogenic PM2.5-related premature mortality estimated with GEMM for the nonaccidental deaths due to noncommunicable diseases and lower respiratory infections rose from 1.26 million (95 % CI: 1.05, 1.46) in 1990 to 2.18 million (95 % CI: 1.84, 2.50) in 2005; then, it decreased to 2.10 million (95 % CI: 1.76, 2.42) in 2015. In 1990, the residential sector was the leading source of the PM2.5-related premature mortality [559,000 (95 % CI: 467,000, 645,900), 44 % of total] in China, followed by industry (29 %), power (13 %), agriculture (9 %) and transportation (5 %). In 2015, the industrial sector became the largest contributor of PM2.5-related premature mortality [734,000 (95 % CI: 615,500, 844,900), 35 % of total], followed by residential (25 %), agriculture (23 %), transportation (10 %) and power (6 %). The decadal changes in source contribution to PM2.5-related premature mortality in China represents a combined impact of socioeconomic development and clean air policy. For example, active control measures have successfully reduced pollution from power sector, while contribution from industrial and transportation sector continuously increased due to more prominent growth of activity rates. Transition in fuel consumption dominated the decrease of contribution from residential sector. In the meanwhile, contribution from agriculture sector continuously increased due to persistent NH3 emissions and enhanced formation of secondary inorganic aerosols under a NH3 rich environment. [ABSTRACT FROM AUTHOR]

The clean air actions implemented by the Chinese government in 2013 have led to significantly improved air quality in Beijing. In this work, we combined the in-situ measurements of the chemical components of submicron particles (PM1) in Beijing during the winters of 2014 and 2017 and a regional chemical transport model to investigate the impact of clean air actions on aerosol chemistry and quantify the relative contributions of anthropogenic emissions, meteorological conditions, and regional transport to the changes in aerosol chemical composition from 2014 to 2017. We found that the average PM1 concentration in winter in Beijing decreased by 49.5% from 2014 to 2017 (from 66.2μgm-3 to 33.4μgm-3). Sulfate exhibited a much larger decline than nitrate and ammonium, which led to a rapid transition from sulfate-driven to nitrate-driven aerosol pollution during the wintertime. Organic aerosol (OA), especially coal combustion OA, and black carbon also showed large decreasing rates, indicating the effective emission control of coal combustion and biomass burning. The decreased sulfate contribution and increased nitrate fraction were highly consistent with the much faster emission reductions in sulfur dioxide (SO2) due to phasing out coal in Beijing compared to reduction in nitrogen oxides emissions estimated by bottom-up inventory. The chemical transport model simulations with these emission estimates reproduced the relative changes in aerosol composition and suggested that the reduced emissions in Beijing and its surrounding regions played a dominant role. The variations in meteorological conditions and regional transport contributed much less to the changes in aerosol concentration and its chemical composition during 2014-2017 compared to the decreasing emissions. Finally, we observed that changes in precursor emissions also altered the aerosol formation mechanisms. The decreased SO2 emissions suppressed the rapid formation of secondary sulfate through heterogeneous reactions. The observed explosive growth of sulfate at a relative humidity (RH) greater than 50% in 2014 was delayed to a higher RH of 70% in 2017. Thermodynamic simulations showed that the decreased sulfate and nitrate concentrations have lowered the aerosol water content, particle acidity, and ammonium particle fraction. The results in this study demonstrated the response of aerosol chemistry to the stringent clean air actions and identified that the anthropogenic emission reductions are a major driver, which could help to further guide air pollution control strategies in China. [ABSTRACT FROM AUTHOR]

Non-methane volatile organic compounds (NMVOC) are important ozone and secondary organic aerosol precursors and play important roles in tropospheric chemistry. In this work, we estimated the total and speciated NMVOC emissions from China’s anthropogenic sources during 1990–2017 by using a bottom-up emission inventory framework, and investigated the main drivers behind the trends. We found that, anthropogenic NMVOC emissions in China have been increased continuously since 1990 due to the dramatic growth in activity rates and absence of effective control measures. We estimated that, anthropogenic NMVOC emissions in China increased from 9.76 Tg in 1990 to 28.5 Tg in 2017, mainly driven by persistent growth from the industry sector and solvent use. In the meanwhile, emissions from the residential and transportation sectors declined after 2005, partly offset the total emission increase. During 1990–2017, mass-based emissions of alkanes, alkenes, alkynes, aromatics, oxygenated VOCs (OVOC) and other species increased by 274 %, 88 %, 4 %, 387 %, 91 %, and 231 % respectively. Following the growth in total NMVOC emissions, the corresponding ozone formation potential (OFP) increased form 38.2 Tg-O3 in 1990 to 99.7 Tg-O3 in 2017. We estimated that aromatics accounted for the largest share (43 %) of total OFP, followed by alkenes (37 %) and OVOC (10 %). Growth in China's NMVOC emissions were mainly driven by the transportation sector before 2000, while industrial sector and solvent use dominated the emission growth during 2000–2010. After 2010, although emissions from the industry sector and solvent use kept growing, strict control measures on transportation and fuel transition in residential stoves have successfully slowed down the increase trend, especially after the implementation of China's clean air action since 2013. However, compared to large emission decreases of other criteria air pollutants in China (e.g., SO2, NOx, and primary PM) during 2013–2017, the relatively flat trend in NMVOC emissions and OFP revealed the absence of effective control measures, which might have contributed to the increase of ozone during the same period. Given their high contributions to emissions and OFP, tailored control measures for solvent use and industrial sources should be developed, and collaborative control strategies should be designed to mitigate both PM2.5 and ozone pollution simultaneously. [ABSTRACT FROM AUTHOR]

A five-year Clean Air Action Plan was implemented in 2013 to reduce air pollutant emissions and improve ambient air quality in Beijing. Assessments of this Action Plan is an essential part of the decision-making process to review the efficacy of the Plan and to develop new policies. Both statistical and chemical transport modelling were applied to assess the efficacy of this Action Plan. However, inherent uncertainties in these methods mean that new and independent methods are required to support the assessment process. Here, we improved a novel machine learning-based random forest technique to quantify the effectiveness of Beijing's Acton Plan by decoupling the impact of meteorology on ambient air quality. Our results demonstrate that meteorological conditions have an important impact on the year to year variations in ambient air quality. Further analysis show that the favorable meteorological conditions in winter 2017 contributed to a lower PM2.5 mass concentration (58 μg m−3) than predicted from the random forest model (61 μg m−3), which is higher than the target of the Plan (2017 annual PM2.5 < 60 μg m−3). However, over the whole period (2013 to 2017), impact of meteorological conditions on the trend of ambient air quality are small. It is the primary emission control, because of the Action Plan, that has led to the significant reduction in PM2.5, PM10, NO2, SO2 and CO from 2013 to 2017, which are approximately 34 %, 24 %, 17 %, 68 %, and 33 % after meteorological correction. The marked decrease in PM2.5 and SO2 is largely attributable to a reduction in coal combustion. Our results indicate that the Action Plan is highly effective in reducing the primary pollution emissions and improving air quality in Beijing. The Action Plan offers a successful example for developing air quality policies in other regions of China and other developing countries. [ABSTRACT FROM AUTHOR]

Beijing has suffered from heavy local emissions as well as regional transport of air pollutants, resulting in severe atmospheric fine particle (PM2.5) pollution. This study developed a combined method to investigate source types of PM2.5 and its source regions during winter 2016 in Beijing, which include receptor model, footprint, and an air quality model. The receptor model was performed with high-time resolution measurements of trace elements, water soluble ions, organic carbon, and elemental carbon using online instruments during the wintertime campaign of the Air Pollution and Human Health-Beijing (APHH-Beijing) program in 2016. Source types and their contributions estimated by the receptor model (Positive Matrix Factorization, PMF) using online measurement were linked with source regions identified by the footprint model, and the regional transport contribution was estimated by an air quality model (the Nested Air Quality Prediction Model System, NAQPMS) to analyze the specific sources and source regions during haze episodes. Our results show that secondary and biomass burning sources were dominated by regional transport while the coal combustion source showed an increased local contribution, suggesting that strict control strategies for local coal combustion in Beijing and a reduction of biomass burning and gaseous precursor emissions in surrounding areas were essential to improve air quality in Beijing. The combination of PMF with footprint results revealed that the secondary source was mainly associated with southern footprints. The northern footprint was characterized by a high dust source contribution (11%) while industrial sources increased with the eastern footprint. The results demonstrated the power of combining receptor model-based source apportionment with other models in understanding the formation of haze episodes and to identify specific sources from different source regions affecting air quality in Beijing. [ABSTRACT FROM AUTHOR]

Since January 1st, 2017, ships berth at the core ports of three designated Domestic Emission Control Area (DECA) in China should use fuel with sulphur content less than or equal to 0.5%. In order to evaluate the impacts of switching fuel, a measurement campaign (SEISO-Bohai) was conducted from 28 December 2016 to 15 January 2017 at JingTang Harbor, an area within the 7th busiest port in the world, including meteorological monitoring, pollutants monitoring, aerosol sampling and fuel sampling. During the campaign, 16 ship plumes were captured by the on-shore measurement sites, and 4 plumes indicates the usage of high SF fuel. The average reduction of average ΔNOx / ΔSO2 ratio from high sulphur plumes (3.26) before January 1st to low sulphur plumes (12.97) after January 1st shows a direct SO2 emission reduction of 75%, consistent with the sulphur content reduction (79%). Average concentrations of PM2.5, NOx, SO2, O3 and CO during campaign were 147.85 μg m-3, 146.93 ppb, 21.91 ppb, 29.68 ppb and 2.21 ppm, respectively, among which NOx reached a maximum hourly concentration of 692.6 ppb and SO2 165.5 ppb. Mean concentrations of carbonaceous and dominant ionic species in particles were 6.52 (EC), 23.10 (OC), 22.04 (SO42-), 25.95 (NO3-) and 13.55 (NH4+) μg m-3. Although the carbonaceous species in particles were not significantly affected by fuel switching, the gas and particle pollutants in ambient air exhibited clear and effective improvements from implementation of low sulphur fuel. Comparison with the prevailing atmospheric conditions and wind map of SO2 variation concluded the prompt SO2 reduction by 70% in ambient air after fuel switching. Given the high humidity in site, this SO2 reduction will abate the amount of secondary aerosols and improve the acidity of particulate matter. Based on enrichment factors of elements in PM2.5, vanadium was identified as marker for residual fuel ship emissions, decreasing significantly by 97.1% from 309.9 ng m-3 before fuel switching and 9.1 ng m-3 after, which indicated a crucial improvement due to the implementation of low sulphur fuel. Ship emissions were proven to be significantly influential both directly and indirectly on port environment and coastal areas around Bohai Bay, in where the population density reaches 650 per square kilometre. The results from this study provide positive impact on air quality of fuel switching and indication of new method on identification of ship fuel type. [ABSTRACT FROM AUTHOR]

In 2013, China's government published the Air Pollution Prevention and Control Action Plan (APPCAP) with a specific target for Beijing, which aims to reduce annual mean PM2.5 concentrations in Beijing to 60m−3 in 2017. During 2013–2017, the air quality in Beijing was significantly improved following the implementation of various emission control measures locally and regionally, with the annual mean PM2.5 concentration decreasing from 89.5m−3 in 2013 to 58m−3 in 2017. As meteorological conditions were more favourable to the reduction of air pollution in 2017 than in 2013 and 2016, the real effectiveness of emission control measures on the improvement of air quality in Beijing has frequently been questioned. In this work, by combining a detailed bottom-up emission inventory over Beijing, the MEIC regional emission inventory, and the WRF-CMAQ model, we attribute the improvement in Beijing's PM2.5 air quality in 2017 (compared to 2013 and 2016) to the following factors: changes in meteorological conditions, reduction of emissions from surrounding regions, and seven specific categories of local emission control measures in Beijing. We collect and summarize data related to 32 detailed control measures implemented during 2013–2017, quantify the emission reductions associated with each measure using the bottom-up local emission inventory in 2013, aggregate the measures into seven categories, and conduct a series of CMAQ simulations to quantify the contribution of different factors to the PM2.5 changes. We found that, although changes in meteorological conditions partly explain the improved PM2.5 air quality in Beijing in 2017 compared to 2013 (3.8m−3, 12.1% of total), the rapid decrease in PM2.5 concentrations in Beijing during 2013–2017 was dominated by local (20.6m−3, 65.4%) and regional (7.1m−3, 22.5%) emission reductions. The seven categories of emission control measures, i.e., Coal-fired boiler control, Clean fuels in the residential sector, Optimized industrial structure, Fugitive dust control, Vehicle emission control, Improved end-of-pipe control, and Integrated treatment of VOCs, reduced the PM2.5 concentrations in Beijing by 5.9, 5.3, 3.2, 2.3, 1.9, 1.8, and 0.2m−3, respectively, during 2013–2017. We also found that if the meteorological conditions in 2017 had remained the same as those in 2016, the annual mean PM2.5 concentrations would have increased from 58m−3 to 63m−3, exceeding the target established in the APPCAP. Despite the remarkable impacts from meteorological condition changes, local and regional emission reductions still played dominant roles in the PM2.5 decrease in Beijing during 2016–2017, and Clean fuels in the residential sector, Coal-fired boiler control, and Optimized industrial structure were the three most effective local measures (contributing reductions of 2.1, 1.9 and 1.5m−3, respectively). Our study confirms the effectiveness of clean air actions in Beijing and its surrounding regions and reveals that a new generation of control measures and strengthened regional joint emission control measures should be implemented for continued air quality improvement in Beijing because the major emitting sources have changed since the implementation of the clean air actions. [ABSTRACT FROM AUTHOR]

With the fast development of seaborne trade and relatively more efforts on reducing emissions from other sources in China, shipping emissions contribute more and more significantly to air pollution. In this study, based on a shipping emission inventory with high spatial and temporal resolution within 200 nautical miles (Nm) to the Chinese coastline, the Community Multiscale Air Quality (CMAQ) model was applied to quantify the impacts of the shipping sector on the annual and seasonal concentrations of PM2.5 for the base year 2015 in China. Emissions within 12 Nm accounted for 51.2 %-56.5 % of the total shipping emissions, and the distinct seasonal variations in spatial distribution were observed. The modeling results showed that shipping emissions increased the annual averaged PM2.5 concentrations in eastern China up to 5.2 µg/m³, and the impacts in YRD (Yangtze River Delta) and PRD (Pearl River Delta) were much greater than those in BTH (Beijing-Tianjin-Hebei). Shipping emissions influenced the air quality in not only coastal areas but also the inland areas hundreds of kilometers (up to 960 km) away from the sea. The impacts on the PM2.5 showed obvious seasonal variability, and patterns in the north and south of the Yangtze river were also quite different. In addition, since the onshore wind can carry ship pollutants to inland areas, the daily contributions of shipping emissions in onshore flow days were about 1.8-2.7 times higher than that in rest of days. A source-oriented CMAQ was used to estimate the contributions of shipping emissions from maritime areas within 0-12 Nm, 12-50 Nm, 50-100 Nm and 100-200 Nm to PM2.5 concentrations. The results indicated that shipping emissions within 12 Nm were the dominant contributor with contributions 30-90 % of the total impacts induced by emissions with 200 Nm. While a relative high contribution (40-60 %) of shipping emissions within 20-100 Nm was observed in the north of PRD region and south of Lianyungang, due to the major water traffic lanes far from land. [ABSTRACT FROM AUTHOR]

To tackle the problem of severe air pollution, China has implemented active clean air policies in recent years. As a consequence, the emissions of major air pollutants have decreased and the air quality has substantially improved. Here, we quantified China's anthropogenic emission trends from 2010–2017 and identified the major driving forces of these trends by using a combination of bottom-up emission inventory and Index Decomposition Analysis (IDA) approaches. The relative change rates of China's anthropogenic emissions during 2010–2017 are estimated as follows: −62 % for SO2, −17 % for NOx, +11 % for NMVOC, +1 % for NH3, −27 % for CO, −38 % for PM10, −35 % for PM2.5, −27 % for BC, −35 % for OC, and +18 % for CO2. The IDA results suggest that emission control measures are the main drivers of this reduction, in which the pollution controls on power plants and industries are the most effective mitigation measures. The emission reduction rates markedly accelerated after the year 2013, confirming the effectiveness of China's Clean Air Action that was implemented in 2013. We estimated that during 2013–2017, China's anthropogenic emissions decreased by 59 % for SO2, 21 % for NOx, 23 % for CO, 36 % for PM10, 33 % for PM2.5, 28 % for BC, and 32 % for OC. NMVOC emissions increased by 11 % and NH3 emissions remained stable from 2010–2017, representing the absence of effective mitigation measures for NMVOC and NH3 in current policies. The relative contributions of different sectors to emissions have significantly changed after several years' implementation of clean air policies, indicating that it is paramount to introduce new policies to enable further emission reductions in the future. [ABSTRACT FROM AUTHOR]

Reducing black carbon (BC) emissions has been recognized as an efficient way to simultaneously improve air quality and mitigate climate change. However, the benefits of BC emission controls are not well quantified partly due to a lack of understanding of the changes in BC light absorption as a result of emission reductions. In this work, we discussed the effects of multi-pollutant emission reductions on the BC light absorption based on a field campaign study conducted before, during and after the 2014 APEC (Asia-Pacific Economic Cooperation) meeting in Beijing, China. When emission restrictions were in place during APEC, we found that the reduction in the light absorption of BC-containing particles was driven by both the decrease in BC mass concentration and the weakened light-absorption capability of BC. Compared with that before and after APEC, the daytime light absorption of BC-containing particles during APEC reduced by ~ 56 %, of which ~ 48 % was contributed by the decrease in BC mass concentration and the remain ~ 8 % was contributed by a weakening of light-absorption capability for BC. Based on single particle soot photometer (SP2) measurement and Mie calculation, we estimated that the light-absorption capability of BC-containing particles with ~ 80–200 nm refractory BC (rBC) cores at daytime during APEC was reduced by ~ 6–15 % and ~ 10–20 % compared with that before and after APEC, respectively. The decrease in BC light-absorption capability could be attributed to less coating materials on BC surfaces as a result of a decreased chemical production of secondary aerosols. Compared with that before and after APEC, the mass ratio between the coating materials and rBC core (~ 80–200 nm) during APEC decreased by ~ 10–30 % and ~ 31–53 %, respectively, due to reductions in coating precursor emissions, e.g., SO2 and NO2. The results revealed the benefits of emission control on BC light absorption by simultaneously reducing the mass concentration and light-absorption capability of BC, implying that synergetic reduction in multiple-pollutant emission could benefit both air quality and climate. [ABSTRACT FROM AUTHOR]

Continuous field observations of haze pollution were conducted in winter and summer during 2015 in Zibo, a highly industrialized city in the North China Plain that is adjacent to the Jing-Jin-Ji area. PM2.5 concentration averaged 146.7 ± 85.8 and 82.2 ± 44.3 μg m−3 in winter and summer, respectively. The chemical component contributions to PM2.5 showed obvious seasonal variation. Organics were high in winter, but secondary inorganic aerosols (SIA) were high in summer. From non-haze to haze days, the concentration of SIA increased, implying an important role of secondary processes in the evolution process of the pollution. The diurnal behavior of several pollutants during haze days appeared to fluctuate more, but during non-haze days, it was much more stable, suggesting that complex mechanisms are involved. Specifically, gaseous precursors, mixed layer height (MLH), photochemical activity, and relative humidity (RH) also played important roles in the diurnal variation of the pollutants. Normally, larger gaseous precursor concentrations, photochemical activity, and RH, and lower MLH favored high concentrations. In winter, the formation of sulfate was mainly influenced by RH, indicating the importance of heterogeneous reactions in its formation. In contrast, in summer, photochemistry and SO2 concentration had the largest impact on the sulfate level. We found that Zibo was an ammonia-rich city, especially in winter, meaning that the formation of nitrate was through homogeneous reactions between HNO3 and NH3 in the gas phase, followed by partitioning into the particle phase. The RH, NO2, and Excess NH4+ were the main influencing factors for nitrate in winter, whereas Excess NH4+, RH, and temperature were the key factors in summer. The secondary organic carbon (SOC) level depended on the MLH and photochemistry. In winter, the effect of the MLH was stronger than that of photochemistry, but a reversed situation occurred in summer because of the intensive photochemistry. Our work suggested that the inter-transport between Zibo, one of the most polluted cities in north China, and its adjacent areas should be taken into account when formulating air pollution control policy. [ABSTRACT FROM AUTHOR]

Compared to the severe winter haze episodes in the North China Plain (NCP), haze pollution during summertime has drawn little public attention. In this study, we present the highly time-resolved chemical composition of submicron particles (PM1) measured in Beijing and Xinxiang in the NCP region during summertime to evaluate the driving factors of aerosol pollution. During the campaign periods (30 June to 27 July, 2015, for Beijing and 8 to 25 June, 2017, for Xinxiang), the average PM1 concentrations were 35.0 μg m−3 and 64.2 μg m−3 in Beijing and Xinxiang, respectively. Pollution episodes characterized with largely enhanced nitrate concentrations were observed at both sites. In contrast to the slightly decreased mass fractions of sulfate, semi-volatile oxygenated organic aerosol (SV-OOA), and low-volatile oxygenated organic aerosol (LV-OOA) in PM1, nitrate displayed an almost linearly increased contribution with the aggravation of aerosol pollution in both Beijing and Xinxiang, highlighting the importance of nitrate formation as the driving force of haze evolution in summer. Rapid nitrate production mainly occurred after midnight, with a higher formation rate than that of sulfate, SV-OOA, or LV-OOA. Detailed investigation of nitrate behaviors revealed several factors influencing the rapid nitrate formation in summer: high ammonia emissions in the NCP region, the gas-to-particle equilibrium of ammonium nitrate closely related to variations in temperature and relative humidity, nighttime nitrate production through heterogeneous hydrolysis of dinitrogen pentoxide (N2O5), and regional transport from different air mass origins. Finally, atmospheric particulate nitrate data acquired by mass spectrometric techniques from various field campaigns in Asia, Europe, and North America uncovered a higher concentration and higher fraction of nitrate present in China. Although measurements in Beijing during different years demonstrate a decline in the nitrate concentration in recent years, the nitrate contribution in PM1 still remains high. To effectively alleviate particulate matter pollution in summer, our results call for the urgent need to initiate ammonia emission control measures and further reduce nitrogen oxide emissions over the NCP region. [ABSTRACT FROM AUTHOR]

Emissions from ships at berth played an important role in the exposure of atmospheric pollutants to high density population in port areas, but these emissions were not understood very well. In this study, volatile organic compounds (VOCs) and particle emissions from 20 container ships at berth were sampled and analyzed during the fuel switch period at Jingtang Port in Hebei Province, China. VOCs and particles were analyzed by gas chromatography-mass spectrometer (GC-MS) and the Single Particle Aerosol Mass Spectrometer (SPAMS), respectively. VOCs analysis showed that alkanes and aromatics, especially benzene, toluene and heavier compounds e.g. n-heptane, n-octane, n-nonane, dominated the total identified species. Secondary organic aerosol yields and ozone forming potential were 0.017 ± 0.007 g SOA/g VOCs and 2.63 ± 0.37 g O3/g VOCs, respectively. Both positive and negative ion mass spectra from individual ship were derived and intensity of specific ions could be quantified. Results showed that element carbon (35.74 %), element carbon-organic carbon mixture (33.95 %) and Na-rich particles (21.12 %) were major classes with a total number ratio of 90.7 %. Particles from ship auxiliary engines were in a size range of 0.2 to 2.5 μm, with a peak occurring at around 0.4 μm. The issue of vanadium as tracer element was discussed that V was not a proper tracer when using low sulfur content diesel oil. The average percentage of sulfate particles from shipping emissions before and after switching to marine diesel oil were 23.82 % and 23.61 % respectively. The total results provide robust evidences in port area air quality assessment and source apportionment. [ABSTRACT FROM AUTHOR]

The impacts of black carbon (BC) aerosols on air quality, boundary layer dynamic and climate depend not only on the BC mass concentration but also on the light absorption capability of BC. It well known that the light absorption capability of BC depends on the amount of coating materials (namely other species on BC by condensation and coagulation). However, the difference of light absorption capability of ambient BC-containing particles under different air pollution conditions (e.g., the air clean and polluted conditions) remains unclear due to the complex aging process of BC in the atmosphere. In this work, we investigated the evolution of light absorption capability for BC-containing particles with changing pollution levels in urban Beijing, China. During the campaign period (17 to 30 November 2014), with the growth of PM1 concentration from ~ 10 μg m−3 to ~ 230 μg m−3, we found that the aging degree and light absorption capability of BC-containing particles with refractory BC cores of ~ 75–200 nm increased by 26–73 % and 13–44 % respectively, indicating stronger light absorption capability of BC-containing particles under more polluted conditions due to more coating materials on the BC surface. By using effective emission intensity (EEI) model, we further found that aging during the regional transport plays an important role in the difference among the light absorption capability of BC-containing particles under different air pollution levels. During the pollution episode, ~ 63 % of the BC over Beijing originated from regional sources outside of Beijing. These regionally sourced BC-containing particles were characterized by more coating materials on BC surface due to accelerated aging process within more polluted air, which contributed ~ 78 % of the increase in light absorption capability of BC observed in Beijing during the polluted period (PM1 of ~ 230 μg m−3) comparing to that in the clean period (PM1 of ~ 10 μg m−3). Due to the increase of light absorption capability of BC associated with air pollution, the direct radiative forcing of BC was estimated to be increased by ~ 20 % based on a simple radiation transfer model. Our work identified an amplification of light absorption and direct radiative forcing under more air polluted environment due to more coating pollutants on BC. The air pollution control measures may, on the other hand, break the amplification effect by reducing both emissions of BC and the coating materials and achieve co-benefits of both air quality and climate. [ABSTRACT FROM AUTHOR]

Fine particle associated with haze pollution threatens the health of more than 400 million people in China. It is therefore of great importance to thoroughly investigate and understand its composition. To determine the physicochemical properties in atmospheric fine particles at the micrometer level, we described a sensitive and feasible surface-enhanced Raman scattering (SERS) method using Ag foil as a substrate. This novel method enhanced the Raman signal intensities up to 10,000 a.u. for ν(NO3-) in fine particles with an enhancement factor of at least 56. The SERS effect of Ag foil was further studied experimentally and theoretically and found to have an enhancement factor of the order of ~104. Size-fractionated real particle samples with aerodynamic diameters of 0.4-2.5μm were successfully collected on a heavy haze day, allowing ready observation of morphology and identification of chemical components, such as soot, nitrates, and sulfates. These results suggest that the Ag foil based SERS technique can be effectively used to determine the microscopic characteristics of individual fine particles, which will help to understand haze formation mechanisms and formulate governance policies. [ABSTRACT FROM AUTHOR]

Air quality is a major environmental concern in China, where premature deaths due to air pollution have exceeded 1 million people per year in recent years. Here, using a novel coupling of economic, physical and epidemiological models, we estimate the premature mortality related to anthropogenic outdoor PM2.5 air pollution in seven regions of China in 2010 and show for the first time how the distribution of these deaths in China is determined by a combination of economic activities and physical transport of pollution in the atmosphere. We find that 33% (338 600 premature deaths) of China's PM2.5-related premature mortality in 2010 were caused by pollutants emitted in a different region of the country and transported in the atmosphere, especially from north to south and from east to west. Trade further extended the cross-regional impact; 56% of (568 900 premature deaths) China's PM2.5-related premature mortality was related to consumption in another region, including 423 800 (42% of total) and 145 100 (14 %) premature deaths from domestic consumption and international trade respectively. Our results indicate that multilateral and multi-stage cooperation under a regional sustainable development framework is in urgent need to mitigate air pollution and related health impacts, and efforts to reduce the health impacts of air pollution in China should be prioritized according to the source and location of emissions, the type and economic value of the emitting activities, and the related patterns of consumption. [ABSTRACT FROM AUTHOR]

Bottom-up emission inventories provide primary understanding of sources of air pollution and essential input of chemical transport models. Focusing on SO2 and NOx, we conducted a comprehensive evaluation of two widely-used anthropogenic emission inventories over China, ECLIPSE and MIX, to explore the potential sources of uncertainties and find the clues in improving emission inventories. We first compared the activity rates and emission factors used in two inventories, and investigated the reasons of differences and the impacts on emission estimates. We found that SO2 emission estimates are consistent between two inventories (with 1 % differences), while NOx emissions in ECLIPSE's estimates are 16 % lower than those of MIX. Discrepancies at sectorial and provincial level are much higher. We then examined the impacts of different inventories on model performance, by using the nested GEOS-Chem model. We finally derived top-down NOx emissions by using the NO2 columns from the Ozone Monitoring Instrument (OMI) and compared with the bottom-up estimates. To our knowledge, this is the first work where source-sector comparisons are made along with the remote sensing retrievals and chemical transport modeling. Through the comparison between bottom-up emission inventories and evaluation with top-down information, we summarized the potential directions for further improvement in inventory development. [ABSTRACT FROM AUTHOR]

Satellite nitrogen dioxide (NO2/observations have been widely used to evaluate emission changes. To determine trends in nitrogen oxides (NOx/emission over China, we used a method independent of chemical transport models to quantify the NOx emissions from 48 cities and seven power plants over China, on the basis of Ozone Monitoring Instrument (OMI) NO2 observations from 2005 to 2015. We found that NOx emissions over 48 Chinese cities increased by 52% from 2005 to 2011 and decreased by 21% from 2011 to 2015. The decrease since 2011 could be mainly attributed to emission control measures in power sector; while cities with different dominant emission sources (i.e., power, industrial, and transportation sectors) showed variable emission decline timelines that corresponded to the schedules for emission control in different sectors. The time series of the derived NOx emissions was consistent with the bottom-up emission inventories for all power plants (r = 0:8 on average), but not for some cities (r = 0:4 on average). The lack of consistency observed for cities was most probably due to the high uncertainty of bottom-up urban emissions used in this study, which were derived from downscaling the regional-based emission data to city level by using spatial distribution proxies. [ABSTRACT FROM AUTHOR]

In this study, a regional coupled climate- chemistry modeling system using the dynamical downscaling technique was established by linking the global Community Earth System Model (CESM) and the regional twoway coupled Weather Research and Forecasting - Community Multi-scale Air Quality (WRF-CMAQ) model for the purpose of comprehensive assessments of regional climate change and air quality and their interactions within one modeling framework. The modeling system was applied over east Asia for a multi-year climatological application during 2006-2010, driven with CESM downscaling data under Representative Concentration Pathways 4.5 (RCP4.5), along with a short-term air quality application in representative months in 2013 that was driven with a reanalysis dataset. A comprehensive model evaluation was conducted against observations from surface networks and satellite observations to assess the model's performance. This study presents the first application and evaluation of the two-way coupled WRF-CMAQ model for climatological simulations using the dynamical downscaling technique. The model was able to satisfactorily predict major meteorological variables. The improved statistical performance for the 2m temperature (T2) in this study (with a mean bias of -0.6 °C) compared with the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-models might be related to the use of the regional model WRF and the bias-correction technique applied for CESM downscaling. The model showed good ability to predict PM2.5 in winter (with a normalized mean bias (NMB) of 6.4%in 2013) and O3 in summer (with an NMB of 18.2% in 2013) in terms of statistical performance and spatial distributions. Compared with global models that tend to underpredict PM2.5 concentrations in China, WRF-CMAQ was able to capture the high PM2.5 concentrations in urban areas. In general, the two-way coupled WRF-CMAQ model performed well for both climatological and air quality applications. The coupled modeling system with direct aerosol feedbacks predicted aerosol optical depth relatively well and significantly reduced the overprediction in downward shortwave radiation at the surface (SWDOWN) over polluted regions in China. The performance of cloud variables was not as good as other meteorological variables, and underpredictions of cloud fraction resulted in overpredictions of SWDOWN and underpredictions of shortwave and longwave cloud forcing. The importance of climate-chemistry interactions was demonstrated via the impacts of aerosol direct effects on climate and air quality. The aerosol effects on climate and air quality in east Asia (e.g., SWDOWN and T2 decreased by 21.8Wm-2 and 0.45 °C, respectively, and most pollutant concentrations increased by 4.8-9.5% in January over China's major cities) were more significant than in other regions because of higher aerosol loadings that resulted from severe regional pollution, which indicates the need for applying online-coupled models over east Asia for regional climate and air quality modeling and to study the important climate-chemistry interactions. This work established a baseline for WRF-CMAQ simulations for a future period under the RCP4.5 climate scenario, which will be presented in a future paper. [ABSTRACT FROM AUTHOR]

Currently, the emission inventory of vehicular volatile organic compounds (VOCs) is one of those with the largest errors and uncertainties due to the imperfection of estimation methods and the lack of first-hand basic data. In this study, an updated speciated emission inventory of VOCs and an estimation of intermediate-volatility organic compounds (IVOCs) from vehicles in China at the provincial level, with a target year of 2015, were developed based on a set of state-of-the-art methods and a mass of local measurement data. The activity data for light-duty vehicles were derived from trajectories of more than 70 thousand cars for one year. The annual mileages of trucks were calculated from reported data by more than 2 million trucks in China. The emission profiles were updated using measurement data. Not only vehicular tailpipe emissions (VTEs) but also four kinds of vehicular evaporation emissions (VEEs), including refuelling, hot soak, diurnal and running loss, were taken into account. The results showed that the total vehicular VOCs emissions in China were 4.21 Tg and the IVOCs emissions were 121.23 Gg in the year of 2015. VTEs were still the predominant contributor, but VEEs were already responsible for 39.20 % of VOCs. Since VEES has a much less strict control standard, it should be paid much more attention to. Among VTEs, passenger vehicles contributed most (49.86 %), followed by trucks (28.15 %) and motorcycles (21.99 %). Among VEEs, running loss was the largest contributor (81.05 %). For both VTEs and VEEs, Guangdong, Shandong and Jiangsu province took the first three spots, with a respective contribution of 10.66 %, 8.85 % and 6.54 % to the total amounts of VOCs from vehicles. Totally, 97 VOC species were analysed in this VOCs emission inventory. I-pentane, toluene and formaldehyde were found to be the most abundant species in China's vehicular VOCs emissions. The estimated IVOCs is other "inconvenient truth", providing insights the precursors of secondary organic aerosol (SOA) from vehicles were much more than previous estimation. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosol particles play an important role in regulating earth's climate and their climate effects depend on their mixing state. During the CAREBeijing 2013 campaign, we measured the size-resolved mixing state of refractory BC particles in North China Plain and performed intercomparison between a single particle soot photometer (SP2) and a volatility tandem differential mobility analyzer (VTDMA). The intercomparison shows a good agreement between the optical particle diameter determined by SP2 and the mobility particle diameter determined by VTDMA for non-BC as well as for internally mixed refractory BC particles. The VTDMA shows a higher concentration of refractory particles than that of the SP2, which suggests the existence of a large fraction of low volatile non-BC aerosols. Following parameters were constrained by closure studies to improve the inversion of the mixing state of ambient BC (i.e., coating thickness (CT) and shell/core ratio (Dp / Dc)) by SP2: a) refractive indices (RI) of 1.42 and 1.67-0.56i for non-BC and rBC core components, respectively, b) refractory BC (rBC) core density of 1.2 g cm-3 for internally-mixed BC particles, and c) an effective density range of 0.25-0.45 g cm-3 for externally-mixed BC particles. Moreover, the upper limit of the measurable particle size of SP2 was extended by the leading-edge-only (LEO) fit from ~ 400 nm to ~ 550 nm as confirmed by the VTDMA measurement. Based on the improved inversion from SP2 measurement, we found that non-BC containing particles, internally-mixed BC and externally-mixed BC contribute 85-90 %, 5-7 % and 5-10 % of the total aerosol number in the size range of 200 nm to 350 nm. The number fraction of internally-mixed BC in total BC-containing aerosols (Fin) shows pronounced diurnal cycles with a peak around noon time and an apparent turnover rate up to 6-9 % h-1. Such diurnal cycles are similar to the finding of Cheng et al. (2012) suggesting the competing effect of emissions and aging processes. In this study, the observed internally-mixed BC particles in the polluted regional NCP (North China Plain) background site (Xianghe) suggest a rapid aging process of BC on the regional scale. During the intensive field study period, ~ 80 % of internally-mixed BC particles at 200-300 nm showed a Dp / Dc ratio of more than 2, accompanying with an average value of 2.3-2.8. Meanwhile, the CT of internally-mixed BC particles (200-350 nm) with rBC core size of 80-200 nm was in the range of 50-150 nm. Compared with previous measurements in developed countries, the observed BC particles on regional scale (i.e., internally-mixed BC particles) were more-aged, indicating stronger optical and climate effect of BC on the regional scale in northern China. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) frequently experiences heavy haze pollution, particularly during wintertime. In winter 2015-2016, the NCP region suffered several extremely severe haze episodes with air pollution red alerts issued in many cities. We have investigated the sources and aerosol evolution processes of the severe pollution episodes in Handan, a typical industrialized city in the NCP region, using real-time measurements from an intensive field campaign during the winter of 2015-2016. The average (±1σ) concentration of submicron aerosol (PM1) during 3 December 2015-5 February 2016 was 187.6 (±137.5) μg m-3, with the hourly maximum reaching 700.8 μg m-3. Organic was the most abundant component, on average accounting for 45 % of total PM1 mass, followed by sulfate (15 %), nitrate (14 %), ammonium (12 %), chloride (9 %) and black carbon (BC, 5 %). Positive matrix factorization (PMF) with the multilinear engine (ME-2) algorithm identified four major organic aerosol (OA) sources, including traffic emissions represented by a hydrocarbon-like OA (HOA, 7 % of total OA), industrial and residential burning of coal represented by a coal combustion OA (CCOA, 29 % of total OA), open and domestic combustion of wood and crop residuals represented by a biomass burning OA (BBOA, 25 % of total OA), and formation of secondary OA (SOA) in the atmosphere represented by an oxygenated OA (OOA, 39 % of total OA). Emissions of primary OA (POA), which together accounted for 61 % of total OA and 27 % of PM1, are a major cause of air pollution during the winter. Our analysis further uncovered that primary emissions from coal combustion and biomass burning together with secondary formation of sulfate (mainly from SO2 emitted by coal combustion) are important driving factors for haze evolution. However, the bulk composition of PM1 showed comparatively small variations between less polluted periods (daily PM2.5 ≤ 75 μg m-3) and severely polluted periods (daily PM2.5 > 75 μg m-3), indicating relatively synchronous increases of all aerosol species during haze formation. The case study of a severe haze episode, which lasted 8 days starting with a steady buildup of aerosol pollution followed by a persistently high level of PM1 (326.7-700.8 μg m-3), revealed the significant influence of stagnant meteorological conditions which acerbate air pollution in the Handan region. The haze episode ended with a shift of wind which brought in cleaner air masses from the northwest of Handan and gradually reduced PM1 concentration to < 50 μg m-3 after 12 h. Aqueous-phase reactions under higher relative humidity (RH) were found to significantly promote the production of secondary inorganic species (especially sulfate) but showed little influence on SOA. [ABSTRACT FROM AUTHOR]

Spatial proxies used in bottom-up emission inventories to derive the spatial distributions of emissions are usually empirical and involve additional levels of uncertainty. Although uncertainties in current emission inventories have been discussed extensively, uncertainties resulting from improper spatial proxies have rarely been evaluated. In this work, we investigate the impact of spatial proxies on the representation of gridded emissions by comparing six gridded NOx emission datasets over China developed from the same magnitude of emissions and different spatial proxies. GEOS-Chem-modeled tropospheric NO2 vertical columns simulated from different gridded emission inventories are compared with satellite-based columns. The results show that differences between modeled and satellite-based NO2 vertical columns are sensitive to the spatial proxies used in the gridded emission inventories. The total population density is less suitable for allocating NOx emissions than nighttime light data because population density tends to allocate more emissions to rural areas. Determining the exact locations of large emission sources could significantly strengthen the correlation between modeled and observed NO2 vertical columns. Using vehicle population and an updated road network for the on-road transport sector could substantially enhance urban emissions and improve the model performance. When further applying industrial gross domestic product (IGDP) values for the industrial sector, modeled NO2 vertical columns could better capture pollution hotspots in urban areas and exhibit the best performance of the six cases compared to satellite-based NO2 vertical columns (slope = 1.01 and R² = 0:85). This analysis provides a framework for information from satellite observations to inform bottom-up inventory development. In the future, more effort should be devoted to the representation of spatial proxies to improve spatial patterns in bottom-up emission inventories. [ABSTRACT FROM AUTHOR]

Gridded emission inventories are essential inputs for chemical transport models and climate models. Spatial proxies are applied to allocate emissions from regional totals to spatially resolved grids when the exact locations of emissions are absent, with additional uncertainties arising due to the spatial mismatch between the locations of emissions and spatial proxies. In this study, we investigate the impact of spatial proxies on the accuracy of gridded emission inventories at different spatial resolutions by comparing gridded emissions developed from different spatial proxies (proxy-based inventory) with a highly spatially disaggregated bottom-up emission inventory developed from the extensive use of locations of emitting facilities (bottom-up inventory) in Hebei Province, China. We find that proxy-based inventories are generally comparable to bottom-up inventories for grid sizes larger than 0.25° because spatial errors are largely diminished at coarse resolutions. However, for gridded emissions with finer resolutions, large positive biases in urban centers and negative biases in suburban and rural regions are identified in proxy-based inventories and are then propagated into significant biases in urban-scale chemical transport modeling. Compared to bottom-up inventories, the use of proxy-based emissions exhibits similar modeling results, with biases varying from 3 to 13 % when predicting surface concentrations of different pollutants at 36 km resolution and an additional 8–73 % at 4 km resolution. The resolution dependence of uncertainties in proxy-based gridded inventories can be explained by the decoupling of emission facility locations from spatial surrogates, especially because industry facilities tend to be located away from urban centers. This distance results in a divergence between emission distributions and the allocation of proxies on smaller grids. The decoupling effects are weakened when the grid size increases to cover both urban and rural regions. We conclude that proxy-based inventories are of sufficient quality to support regional and global models (larger than 0.25° in this case study); however, to support urban-scale models with accurate emission inputs, bottom-up inventories incorporating the exact locations of emitting facilities should be developed instead of proxy-based inventories. [ABSTRACT FROM AUTHOR]

The accuracy of China's energy statistics is of great concern because it contributes greatly to the uncertainties in estimates of global emissions. This study attempts to improve the understanding of uncertainties in China's energy statistics and evaluate their impacts on China's emissions during the period of 1990–2013. We employed the Multi-resolution Emission Inventory for China (MEIC) model to calculate China's emissions based on different official data sets of energy statistics using the same emission factors. We found that the apparent uncertainties (maximum discrepancy) in China's energy consumption increased from 2004 to 2012, reaching a maximum of 646 Mtce (million tons of coal equivalent) in 2011 and that coal dominated these uncertainties. The discrepancies between the national and provincial energy statistics were reduced after the three economic censuses conducted during this period, and converging uncertainties were found in 2013. The emissions calculated from the provincial energy statistics are generally higher than those calculated from the national energy statistics, and the apparent uncertainty ratio (the ratio of the maximum discrepancy to the mean value) owing to energy uncertainties in 2012 took values of 30.0, 16.4, 7.7, 9.2 and 15.6 %, for SO2, NOx, VOC, PM2.5 and CO2 emissions, respectively. SO2 emissions are most sensitive to energy uncertainties because of the high contributions from industrial coal combustion. The calculated emission trends are also greatly affected by energy uncertainties – from 1996 to 2012, CO2 and NOx emissions, respectively, increased by 191 and 197 % according to the provincial energy statistics but by only 145 and 139 % as determined from the original national energy statistics. The energy-induced emission uncertainties for some species such as SO2 and NOx are comparable to total uncertainties of emissions as estimated by previous studies, indicating variations in energy consumption could be an important source of China's emission uncertainties. [ABSTRACT FROM AUTHOR]

The MIX inventory is developed for the years 2008 and 2010 to support the Model Inter-Comparison Study for Asia (MICS-Asia) and the Task Force on Hemispheric Transport of Air Pollution (TF HTAP) by a mosaic of up-to-date regional emission inventories. Emissions are estimated for all major anthropogenic sources in 29 countries and regions in Asia. We conducted detailed comparisons of different regional emission inventories and incorporated the best available ones for each region into the mosaic inventory at a uniform spatial and temporal resolution. Emissions are aggregated to five anthropogenic sectors: power, industry, residential, transportation, and agriculture. We estimate the total Asian emissions of 10 species in 2010 as follows: 51.3 Tg SO2, 52.1 Tg NOx, 336.6 Tg CO, 67.0 Tg NMVOC (non-methane volatile organic compounds), 28.8 Tg NH3, 31.7 Tg PM10, 22.7 Tg PM2.5, 3.5 Tg BC, 8.3 Tg OC, and 17.3 Pg CO2. Emissions from China and India dominate the emissions of Asia for most of the species. We also estimated Asian emissions in 2006 using the same methodology of MIX. The relative change rates of Asian emissions for the period of 2006–2010 are estimated as follows: −8.1 % for SO2, +19.2 % for NOx, +3.9 % for CO, +15.5 % for NMVOC, +1.7 % for NH3, −3.4 % for PM10, −1.6 % for PM2.5, +5.5 % for BC, +1.8 % for OC, and +19.9 % for CO2. Model-ready speciated NMVOC emissions for SAPRC-99 and CB05 mechanisms were developed following a profile-assignment approach. Monthly gridded emissions at a spatial resolution of 0.25°  ×  0.25° are developed and can be accessed from http://www.meicmodel.org/dataset-mix. [ABSTRACT FROM AUTHOR]

We estimated the changes in chemical composition of ambient PM2.5 over China during 2005-2012 using satellite-based aerosol optical depth (AOD) data and the GEOS-Chem chemical transport model, and investigated the driving forces behind the changes by examining the changes in precursor emissions using a bottom-up emission inventory. We found that the national population-weighted mean PM2.5 concentration increased from 63.9 μg/m³ in 2005 to 75.2 μg/m³ in 2007 (+18.19 % per year), and subsequently decreased to 66.9 μg/m³ from 2007 to 2012 (-2.67 % per year), composing a flat trend of population-weighted mean PM2.5 concentration during 2005-2012. Variations in PM2.5 concentrations are mainly driven by the changes in sulfate and nitrate concentrations. Population-weighted mean sulfate concentration increased by 10.72 % from 2005-2006 (from 14.4 μg/m³ to 15.9 μg/m³) and then decreased by 4.30 % per year from 2006-2012, dominating the variations of total PM2.5 concentrations. The decrease of sulfate concentration is partly offset by the increase of nitrate concentration: population-weighted mean nitrate concentration increased by 3.39 % per year during 2005-2012 (from 9.8 μg/m³ to 12.2 μg/m³). The changes in sulfate and nitrate concentrations were in line with the changes in SO2 and NOx emissions during the same period. By examining the emission data from the MEIC emission inventory, we found that the desulfurization regulation enforced around 2005 in power plants was the primary contributor to the SO2 emissions reduction since 2006. In contrast, growth of energy consumption and lack of control measures for NOx resulted in persistent increase in NOx emissions until the installation of denitrification devices on power plants late in 2011, which began to take effect in 2012. The results of this work indicate that the synchronized abatement of emissions for multi-pollutants are necessary for reducing ambient PM2.5 concentrations over China. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) frequently encountered heavy haze pollution in recent years, particularly during wintertime. In 2015-2016 winter, the NCP region suffered several extremely severe haze episodes with air pollution red alerts issued in many cities. In this work, we investigated the sources and aerosol evolution processes of the severe pollution episodes in Handan, a typical industrialized city in the NCP region, using real-time measurements from an intensive field campaign during the winter of 2015-2016. The average (± 1σ) concentration of submicron aerosol (PM1) during December 3, 2015-February 5, 2016 was 187.6 (± 137.5) μg m-3, with the hourly maximum reaching 700.8 μg m-3. Organic was the most abundant component, on average accounting for 45 % of total PM1 mass, followed by sulfate (15 %), nitrate (14 %), ammonium (12 %), chloride (9 %) and BC (5 %). Positive matrix factorization (PMF) with multi-linear engine (ME-2) identified four major organic aerosol (OA) sources, including traffic emissions represented by a hydrocarbon-like OA (HOA, 7 % of total OA), industrial and residential burning of coal represented by a coal combustion OA (CCOA, 29 % of total OA), open and domestic combustion of wood and crop residuals represented by a biomass burning OA (BBOA, 25 % of total OA), and formation of secondary OA (SOA) in the atmosphere represented by an oxygenated OA (OOA, 39 % of total OA). Emissions of primary OA (POA), which together accounted for 61 % of total OA and 27 % of PM1, are a major cause of air pollution in this region during the winter. Our analysis further uncovered that, primary emissions from coal combustion and biomass burning together with secondary formation of sulfate (mainly from SO2 emitted by coal combustion) are important driving factors for haze evolution. However, the bulk composition of PM1 showed comparatively small variations between less polluted periods (daily PM2.5 ≤ 75 μg m-3) and severely polluted periods (daily PM2.5 > 75 μg m-3), indicating relatively synchronous increases of all aerosol species during haze formation. The case study of a severe haze episode, which lasted 8 days starting with a steady build-up of aerosol pollution followed by a persistently high level of PM1 (326.7-700.8 μg m-3), revealed the significant influences of stagnant meteorological conditions on acerbating air pollution problems in the Handan region. The haze episode ended with a shift of wind which brought in cleaner air masses from the northwest of Handan and gradually reduced PM1 concentration to < 50 μg m-3 after 12 hours. Furthermore, aqueous-phase reactions under higher relative humidity (RH) were found to significantly promote the production of secondary inorganic species (especially sulfate), but showed little influence on SOA. [ABSTRACT FROM AUTHOR]

Gridded emission inventories are essential inputs for chemical transport models and climate models. Spatial proxies are applied to allocate emissions from regional totals to spatially resolved grids when the exact locations of emissions are absent, with additional uncertainties arising due to the spatial mismatch between the locations of emissions and spatial proxies. In this study, we investigate the impact of spatial proxies on the accuracy of gridded emission inventories at different spatial resolutions by comparing gridded emissions developed from different spatial proxies (proxy-based inventory) with a highly spatially disaggregated bottom-up emission inventory developed from the extensive use of locations of emitting facilities (bottom-up inventory) in Hebei Province, China. We find that proxy-based inventories are generally comparable to bottom-up inventories for grid sizes larger than 0.25° because spatial errors are largely diminished at coarse resolutions. However, for gridded emissions with finer resolutions, large positive biases in urban centers and negative biases in suburban and rural regions are identified in proxy-based inventories and are then propagated into significant biases in urban-scale chemical transport modeling. Compared to bottom-up inventories, the use of proxy-based emissions exhibits similar modeling results, with biases varying from 3%-13% in predicting surface concentrations of different pollutants at 36 km resolution and an additional 8%-73% at 4 km resolution. The resolution dependence of uncertainties in proxy-based gridded inventories can be explained by the decoupling of emission facility locations from spatial surrogates, especially because industry facilities tend to be located away from urban centers. This distance results in a divergence between emission distributions and the allocation of proxies on smaller grids. The decoupling effects are weakened when the grid size increases to cover both urban and rural regions. We conclude that proxy-based inventories are of sufficient quality to support regional and global models (larger than 0.25° in this case study); however, to support urban-scale models with accurate emission inputs, bottom-up inventories incorporating the exact locations of emitting facilities should be developed instead of proxy-based inventories. [ABSTRACT FROM AUTHOR]

In this study, a regional coupled climate-chemistry modeling system using the dynamical downscaling technique was established by linking the global Community Earth System Model (CESM) and the regional online coupled Weather Research and Forecasting - Community Multiscale Air Quality (WRF-CMAQ) model for the purpose of comprehensive assessments of regional climate change and air quality and their interactions within one modeling framework. The modeling system was applied over East Asia for a multiyear climatological application during 2006-2010 driven with CESM downscaling data under Representative Concentration Pathway 4.5 (RCP 4.5) as well as a short-term air quality application in representative months in 2013 driven with a reanalysis dataset. A comprehensive model evaluation was conducted against observations from surface networks and satellite observations to assess the model's performance. This study presents the first application and evaluation of the online coupled WRF-CMAQ model for climatological simulations using the dynamical downscaling technique. The model was able to satisfactorily predict major meteorological variables. The improved statistical performance for the 2-m temperature (T2) in this study compared with the Coupled Model Inter-comparison Project Phase 5 (CMIP5) multi-models might be related to the use of the regional model WRF and the bias-correction technique applied for CESM downscaling. The model showed good ability to predict PM2.5 in winter and O3 in summer in terms of statistical performance and spatial distributions. Compared with global models that tend to underpredict PM2.5 concentrations in China, WRF-CMAQ was able to capture the high PM2.5 concentrations in urban areas. In general, the online coupled WRF-CMAQ model performed well for both climatological and air quality applications. The coupled modeling system with direct aerosol feedbacks predicted aerosol optical depth relatively well and significantly reduced the overprediction in downward shortwave radiation at the surface (SWDOWN) over polluted regions in China. The performance of cloud variables was not as good as other meteorological variables, and underpredictions of cloud fraction resulted in overpredictions of SWDOWN and underpredictions of shortwave and longwave cloud forcing. The importance of climate-chemistry interactions was demonstrated via the impacts of aerosol direct effects on climate and air quality. The aerosol effects on climate and air quality in East Asia were more significant than in other regions because of higher aerosol loadings that resulted from severe regional pollution, which indicates the need for applying online-coupled models over East Asia for regional climate and air quality modeling and to study the important climate-chemistry interactions. [ABSTRACT FROM AUTHOR]

The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project that includes characterization of chemical and physical attributes of aerosols from filter samples collected worldwide. This paper discusses the ongoing efforts of SPARTAN to define and quantify major ions and trace metals found in fine particulate matter (PM2:5). Our methods infer the spatial and temporal variability of PM2:5 in a cost-effective manner. Gravimetrically weighed filters represent multi-day averages of PM2:5, with a collocated nephelometer sampling air continuously. SPARTAN instruments are paired with AErosol RObotic NETwork (AERONET) sun photometers to better understand the relationship between ground-level PM2:5 and columnar aerosol optical depth (AOD). We have examined the chemical composition of PM2:5 at 12 globally dispersed, densely populated urban locations and a site at Mammoth Cave (US) National Park used as a background comparison. So far, each SPARTAN location has been active between the years 2013 and 2016 over periods of 2-26 months, with an average period of 12 months per site. These sites have collectively gathered over 10 years of quality aerosol data. The major PM2:5 constituents across all sites (relative contribution±SD) are ammoniated sulfate (20%±11%), crustal material (13.4% ±9.9%), equivalent black carbon (11.9%±8.4%), ammonium nitrate (4.7%±3.0%), sea salt (2.3%± 1.6%), trace element oxides (1.0%±1.1%), water (7.2% ±3.3%) at 35% RH, and residual matter (40%±24%). Analysis of filter samples reveals that several PM2:5 chemical components varied by more than an order of magnitude between sites. Ammoniated sulfate ranges from 1.1 µgm-3 (Buenos Aires, Argentina) to 17 µgm-3 (Kanpur, India in the dry season). Ammonium nitrate ranged from 0.2 µgm-3 (Mammoth Cave, in summer) to 6.8 µgm-3 (Kanpur, dry season). Equivalent black carbon ranged from 0.7 µgm-3 (Mammoth Cave) to over 8 µgm-3 (Dhaka, Bangladesh and Kanpur, India). Comparison of SPARTAN vs. coincident measurements from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network at Mammoth Cave yielded a high degree of consistency for daily PM2:5 (r² = 0.76, slopeD1.12), daily sulfate (r² = 0.86, slopeD1.03), and mean fractions of all major PM2:5 components (within 6%). Major ions generally agree well with previous studies at the same urban locations (e.g. sulfate fractions agree within 4% for 8 out of 11 collocation comparisons). Enhanced anthropogenic dust fractions in large urban areas (e.g. Singapore, Kanpur, Hanoi, and Dhaka) are apparent from high Zn : Al ratios. The expected water contribution to aerosols is calculated via the hygroscopicity parameter Kv for each filter. Mean aggregate values ranged from 0.15 (Ilorin) to 0.28 (Rehovot). The all-site parameter mean is 0.20±0.04. Chemical composition and water retention in each filter measurement allows inference of hourly PM2:5 at 35% relative humidity by merging with nephelometer measurements. These hourly PM2:5 estimates compare favourably with a beta attenuation monitor (MetOne) at the nearby US embassy in Beijing, with a coefficient of variation r² = 0.67 (n = 3167), compared to r² = 0.62 when Kv was not considered. SPARTAN continues to provide an open-access database of PM2:5 compositional filter information and hourly mass collected from a global federation of instruments. [ABSTRACT FROM AUTHOR]

The accuracy of China's energy statistics is of great concern because it contributes greatly to the uncertainties in estimates of global emissions. This study attempts to improve the understanding of uncertainties in China's energy statistics and evaluate their impacts on China's emissions during the period of 1990-2013. We employed the Multi-resolution Emission Inventory for China (MEIC) model to calculate China's emissions based on different official datasets of energy statistics using the same emission factors. We found that the apparent uncertainties (maximum discrepancy) in China's energy consumption increased from 2004 to 2012, reaching a maximum of 646 Mtce (million tons of coal equivalent) in 2011, and that coal dominated these uncertainties. The discrepancies between the national and provincial energy statistics were reduced after the three economic censuses conducted during this period, and converging uncertainties were found in 2013. The emissions calculated from the provincial energy statistics are generally higher than those calculated from the national energy statistics, and the apparent uncertainty ratio (the ratio of the maximum discrepancy to the mean value) owing to energy uncertainties in 2012 took values of 30.0%, 16.4%, 7.7%, 9.2% and 15.6%, for SO2, NOx, VOC, PM2.5 and CO2 emissions, respectively. SO2 emissions are most sensitive to energy uncertainties because of the high contributions from industrial coal combustion. The calculated emission trends are also greatly affected by energy uncertainties - from 1996 to 2012, CO2 and NOx emissions, respectively, increased by 191% and 197% according to the provincial energy statistics but by only 145% and 139% as determined from the original national energy statistics. The energy-induced emission uncertainties for some species such as SO2 and NOx are comparable to total uncertainties of emissions as estimated by previous studies, indicating variations at energy consumption could be an important source of China's emission uncertainties. [ABSTRACT FROM AUTHOR]

Extremely severe haze weather events occurred in many cities in China, especially in the east part of the country, in January 2013. Comprehensive measurements including hourly concentrations of PM2.5 and its major chemical components (water-soluble inorganic ions, organic carbon (OC), and elemental carbon (EC)) and related gas-phase precursors were conducted via an online monitoring system in Suzhou, a medium-sized city in Jiangsu province, just east of Shanghai. PM2.5 (particulate matter with an aerodynamic diameter of 2.5 µm or less) frequently exceeded 150 µgm-3 on hazy days, with the maximum reaching 324 µgm-3 on 14 January 2013. Unfavorable weather conditions (high relative humidity (RH), and low rainfall, wind speed, and atmospheric pressure) were conducive to haze formation. High concentrations of secondary aerosol species (including SO42-, NO-3-, NHC4+, and SOC) and gaseous precursors were observed during the first two haze events, while elevated primary carbonaceous species emissions were found during the third haze period, pointing to different haze formation mechanisms. Organic matter (OM), (NH4)2SO4, and NH4NO3 were found to be the major contributors to visibility impairment. High concentrations of sulfate and nitrate might be explained by homogeneous gas-phase reactions under low RH conditions and by heterogeneous processes under relatively high RH conditions. Analysis of air mass trajectory clustering and potential source contribution function showed that aerosol pollution in the studied areas was mainly caused by local activities and surrounding sources transported from nearby cities. [ABSTRACT FROM AUTHOR]

We present a new method to quantify NOx emissions and corresponding atmospheric lifetimes from OMI NO2 observations together with ECMWF wind fields without further model input for sources located in a polluted background. NO2 patterns under calm wind conditions are used as proxy for the spatial patterns of NOx emissions, and the effective atmospheric NOx lifetime is determined from the change of spatial patterns measured at larger wind speeds. Emissions are subsequently derived from the NO2 mass above the background, integrated around the source of interest. Lifetimes and emissions are estimated for 17 power plants and 53 cities located in non-mountainous regions across China and the USA. The derived lifetimes for the ozone season (May-September) are 3.8±1.0 h (mean±standard deviation) with a range of 1.8 to 7.5 h. The derived NOx emissions show generally good agreement with bottom-up inventories for power plants and cities. Regional inventory shows better agreement with top-down estimates for Chinese cities compared to global inventory, most likely due to different downscaling approaches adopted in the two inventories. [ABSTRACT FROM AUTHOR]

The morphology and density of black carbon (BC) cores in internally mixed BC (In-BC) particles affect their mixing state and absorption enhancement. In this work, we developed a new method to measure the morphology and effective density of the BC cores of ambient In-BC particles using a single-particle soot photometer (SP2) and a volatility tandem differential mobility analyzer (VTDMA) during the CAREBeijing-2013 campaign from 8 to 27 July 2013 at Xianghe Observatory. This new measurement system can select size-resolved ambient In-BC particles and measure the mobility diameter and mass of the In-BC cores. The morphology and effective density of the ambient In- BC cores are then calculated. For the In-BC cores in the atmosphere, changes in their dynamic shape factor (X) and effective density (ρeff) can be characterized as a function of the aging process (Dp/Dc) measured by SP2 and VTDMA. During an intensive field study, the ambient In-BC cores had an average shape factor X of ~1.2 and an average density of ~1.2 g cm-3, indicating that ambient In-BC cores have a near-spherical shape with an internal void of ~30 %. From the measured morphology and density, the average shell / core ratio and absorption enhancement (Eab) of ambient BC were estimated to be 2.1-2.7 and 1.6-1.9, respectively, for In-BC particles with sizes of 200-350 nm. When the In-BC cores were assumed to have a void-free BC sphere with a density of 1.8 g cm-3, the shell / core ratio and Eab were overestimated by ~13 and ~17 %, respectively. The new approach developed in this work improves the calculations of the mixing state and optical properties of ambient In-BC particles by quantifying the changes in the morphology and density of ambient In-BC cores during aging. [ABSTRACT FROM AUTHOR]