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PM is the key pollutant in atmospheric pollution in China. With new national air quality standards taking effect, PM has become a major issue for future pollution control. To effectively prevent and control PM, its emission sources must be precisely and thoroughly understood. However, there are few publications reporting comprehensive and systematic results of PM source apportionment in the country. Based on PM sampling during 2009 in Shenzhen and follow-up investigation, positive matrix factorization (PMF) analysis has been carried out to understand the major sources and their temporal and spatial variations. The results show that in urban Shenzhen (University Town site), annual mean PM concentration was 42.2 μg m, with secondary sulfate, vehicular emission, biomass burning and secondary nitrate as major sources; these contributed 30.0%, 26.9%, 9.8% and 9.3% to total PM, respectively. Other sources included high chloride, heavy oil combustion, sea salt, dust and the metallurgical industry, with contributions between 2%-4%. Spatiotemporal variations of various sources show that vehicular emission was mainly a local source, whereas secondary sulfate and biomass burning were mostly regional. Secondary nitrate had both local and regional sources. Identification of secondary organic aerosol (SOA) has always been difficult in aerosol source apportionment. In this study, the PMF model and organic carbon/elemental carbon (OC/EC) ratio method were combined to estimate SOA in PM. The results show that in urban Shenzhen, annual SOA mass concentration was 7.5 μg m, accounting for 57% of total organic matter, with precursors emitted from vehicles as the major source. This work can serve as a case study for further in-depth research on PM pollution and source apportionment in China. [ABSTRACT FROM AUTHOR]

Haze in China is primarily caused by high pollution of atmospheric fine particulates (PM 2.5 ). However, the detailed source structures of PM 2.5 light extinction have not been well established, especially for the roles of various organic aerosols, which makes haze management lack specified targets. This study obtained the mass concentrations of the chemical compositions and the light extinction coefficients of fine particles in the winter in Dongguan, Guangdong Province, using high time resolution aerosol observation instruments. We combined the positive matrix factor (PMF) analysis model of organic aerosols and the multiple linear regression method to establish a quantitative relationship model between the main chemical components, in particular the different sources of organic aerosols and the extinction coefficients of fine particles with a high goodness of fit ( R 2 = 0.953). The results show that the contribution rates of ammonium sulphate, ammonium nitrate, biomass burning organic aerosol (BBOA), secondary organic aerosol (SOA) and black carbon (BC) were 48.1%, 20.7%, 15.0%, 10.6%, and 5.6%, respectively. It can be seen that the contribution of the secondary aerosols is much higher than that of the primary aerosols (79.4% versus 20.6%) and are a major factor in the visibility decline. BBOA is found to have a high visibility destroying potential, with a high mass extinction coefficient, and was the largest contributor during some high pollution periods. A more detailed analysis indicates that the contribution of the enhanced absorption caused by BC mixing state was approximately 37.7% of the total particle absorption and should not be neglected. [ABSTRACT FROM AUTHOR]

Over the last decade, the Pearl River Delta (PRD) region has seen substantial improvements in PM 2.5 concentrations, which can be attributed to both local emission reductions and nationwide efforts. To formulate effective strategies for long-term PM 2.5 mitigation in the PRD, it is essential to understand the benefits derived from emission reductions in various regions. In this study, we employed a simulation-based decomposition analysis to evaluate the impact of national and local emission changes on PM 2.5 and its composition in the PRD region from 2006 to 2020. The downturn in annual average PM 2.5 concentrations in the PRD region from 2006 to 2020 primarily stems from local emission reductions, constituting 41–55% of the overall improvement, and nationwide emission reductions (excluding those within the PRD), which add another 10–28% to the improvement. The PM 2.5 improvement associated with local emission reduction primarily originates from industrial sources, power plants, and vehicles. Both local and nationwide emission reductions significantly curtail sulfate concentrations, but their impact on nitrate concentrations are relatively moderate, impeded by the ozone rebound due to the inappropriate reduction ratio of NO x /VOCs emissions, particularly in regions with VOCs-limited regime. Since 2013, as a result of China's accelerated efforts to reduce air pollution, national emission reductions have played a larger role in reducing PM 2.5 concentrations in the PRD region, especially in the autumn and winter seasons when their contributions to PM 2.5 decline can reach 44% and 54%, respectively. Therefore, comprehensive ozone control as well as coordinated regional emission reductions will be crucial for the long-term improvement of PM 2.5 in the PRD. Furthermore, stricter measures remain imperative to reduce emissions from local sources such as vehicles, agricultural sources, non-road sources, and dust sources. • The improvement and the compositional change of PM 2.5 in the PRD region were primarily attributed to emission reductions. • Local emission reductions have played a dominant role in improving PM 2.5 levels, while the influence of nationwide efforts is growing. • Local emission reductions from industry sources, power plants, and vehicles drive PM 2.5 improvement. [ABSTRACT FROM AUTHOR]

Road traffic is one of the major sources of particulate matters in the atmosphere. Tunnels provide a semi-closed place to measure traffic-derived particles before the particles were photo-chemically modified in the open air. In this study, aerosol particles were collected in a tunnel, and an urban site for comparison at a coastal city in south China. The particles were analyzed by using a transmission electron microscope coupled with an energy-dispersive X-ray spectrometry. There were four groups of particles according to sources: tailpipe-emitted particles, wear debris, road dust, and secondary particles. Tailpipe-emitted particles included soot, organic, and a part of sulfate and metal particles. Wear debris were characterized by their distinct metal components. Road dust was composed of mineral particles and fly ash. Secondary particles were some sulfate particles and mixture particles. Sulfate particles were further divided into two subtypes: with and without organic coating. Sulfate particles with organic coating accounted for 56.2% of total sulfate particles in the tunnel, while the percentage was 36.9% at the urban site, indicating that sulfate particles were more easily coated by organics in the tunnel than the urban site. However, the aging degree of sulfate particles in the tunnel was weaker than that at the urban site, which was attributed to the absence of photochemical reactions in the tunnel environment. Some mixture particles had a core-shell structure (C-S particles). The composition and morphologies of the cores of the C-S particles were similar to those of mineral, metal, and mixture particles. The shells of the C-S particles were mainly composed of organics. The C-S particles were more aged than the sulfate particles with coating in the tunnel environment, suggesting that mineral and metal components could efficiently enhance particle aging in the absence of photochemical reactions. [ABSTRACT FROM AUTHOR]

In recent years, fine particulate matter (PM) pollution and visibility degradation have become severe air quality issues in China. In this study, PM 2.5 pollution over the Pearl River Delta (PRD) region during January, April, August, and November 2009 was simulated using the Community Multiscale Air Quality (CMAQ) model. An in-depth diagnostic analysis, focused on November 2009, was also conducted to reveal the patterns of sulfate and nitrate distribution, and to identify the main factors that influence the formation of sulfate and nitrate under typical meteorological conditions. The CMAQ model reasonably reproduced the observed concentrations, but showed better performance for January and November than it did for April and August, for which there was light-moderate underestimation of SO 2 , NO x , O 3 , PM 10 , and PM 2.5 concentrations, and slight overestimation of daily 8-h maximum concentrations of O 3 . Utilizing a sulfate tracking technique, it was found that on nearly 20 days in November 2009, characterized by northeasterly winds, cross-boundary transport contributed to >75% of the total sulfate budget, while local gas phase oxidation and primary emissions averaged 10% and 8%, respectively. Aqueous sulfate typically contributed less than 1% of the total sulfate budget, except when the winds were directed from the sea and high humidity favored aqueous oxidation, and the percentage contribution reached up to 46%. NH 3 was generally sufficient to fully neutralize H 2 SO 4 ; however, the formation of nitrate over the PRD was limited by the availability of NH 3 . [ABSTRACT FROM AUTHOR]