Accurate identification of key VOCs sources contributing to O3 formation along the Liaodong Bay based on emission inventories and ambient observations.

In order to achieve the precise control of the volatile organic compounds (VOCs) species with high ozone (O3) formation contribution from key sources in Panjin and Yingkou, two coastal industrial cities with severe O3 pollution along the Liaodong Bay, northeast China, the ambient concentrations of 99 VOCs species were measured online at urban-petrochemical (XLT), suburban-industrial (PP), and rural (XRD) sites in July 2019, contemporary monthly anthropogenic VOCs emission inventories were developed. The source contribution of ambient VOCs resolved by positive matrix factorization (PMF) model was comparable with emission inventories, and the location of VOCs sources were speculated by potential source contribution function (PSCF). 17.5 Gg anthropogenic VOCs was emitted in Panjin and Yingkou in July 2019 with potential to form 54.7 Gg-O3 estimated by emission inventories. The average VOC mixing ratios of 47.1, 26.7, and 16.5 ppbv was observed at XLT, PP, and XRD sites, respectively. Petroleum industry (22 %), organic chemical industry (21 %), and mobile vehicle emission (19 %) were identified to be the main sources contributing to O3 formation at XLT site by PMF, while it is organic chemical industry (33 %) and solvent utilization (28 %) contributed the most at PP site. Taking the subdivided source contributions of emission inventories and source locations speculated by PSCF into full consideration, organic raw chemicals manufacturing, structural steel coating, petroleum refining process, petroleum products storage and transport, off-shore vessels, and passenger cars were identified as the key anthropogenic sources. High O3-formation contribution sources, organic chemical industry and solvent utilization were located in the industrial parks at the junction of the two cities and the southeast of Panjin, and petroleum industry distributed in the whole Panjin and offshore areas. These results identify the key VOCs species and sources and speculate the potential geographical location of sources for precisely controlling ground-level O3 along the Liaodong Bay.

Emission trends of industrial VOCs in China since the clean air action and future reduction perspectives.

Spatiotemporal change patterns of China's industrial VOCs emissions were explored in response to integrated air quality control policies during 2013-2019, and future emissions predicted under the two different scenarios targeting 2030. China's industrial VOCs emissions were decreased to 15.72 Tg in 2019, of which chemical industry, industrial painting, petroleum industry, coal-coking industry, and other industries respectively accounted for 31.0%, 23.9%, 15.6%, and 13.0%, 16.3%, after peaking at 16.40 Tg in 2016. VOC emissions from the petroleum industry and industrial painting showed a continuous increase, with emissions increasing by 0.46 Tg and 0.71 Tg. VOC emissions from the chemical industries increased by 0.91 Tg during 2013-2016 and decreased by 0.72 Tg during 2016-2019. Industrial VOCs emissions in the Beijing-Tianjin-Hebei, Shandong Peninsula, and Central Plain in 2019 respectively reduced by 12.0%, 3.2%, and 8.7% compared to 2013 due to stringent control measures and closure/relocation of highly polluting enterprises. By contrast, industrial VOCs emissions in the West Coast of the Strait and the Central Guizhou increased by 38.1% and 31.8% during 2013-2019. In summary, China's industrial high VOCs emission areas were shifting from key areas to its surrounding areas, resulting in little change in total VOCs emissions. The coal-coking industry, architectural painting, petroleum refining, and pharmaceutical industry will have the most considerable reduction responsibility to reduce VOCs emissions in the future. Guangdong, Jiangsu, Shandong, and Zhejiang will share the highest reduction responsibility, accounting for approximately 40% of national emission reduction.

Significant contrasts in aerosol acidity between China and the United States.

Aerosol acidity governs several key processes in aerosol physics and chemistry, thus affecting aerosol mass and composition and ultimately climate and human health. Previous studies have reported aerosol pH values separately in China and the United States (USA), implying different aerosol acidity between these two countries. However, there is debate about whether mass concentration or chemical composition is the more important driver of differences in aerosol acidity. A full picture of the pH difference and the underlying mechanisms responsible is hindered by the scarcity of simultaneous measurements of particle composition and gaseous species, especially in China. Here we conduct a comprehensive assessment of aerosol acidity in China and the USA using extended ground-level measurements and regional chemical transport model simulations. We show that aerosols in China are significantly less acidic than in the USA, with pH values 1-2 units higher. Based on a proposed multivariable Taylor series method and a series of sensitivity tests, we identify major factors leading to the pH difference. Compared to the USA, China has much higher aerosol mass concentrations (gas + particle, by a factor of 8.4 on average) and a higher fraction of total ammonia (gas + particle) in the aerosol composition. Our assessment shows that the differences in mass concentrations and chemical composition play equally important roles in driving the aerosol pH difference between China and the USA - increasing the aerosol mass concentrations (by a factor of 8.4) but keeping the relative component contributions the same in the USA as the level in China increases the aerosol pH by ~1.0 units and further shifting the chemical composition from US conditions to China's that are richer in ammonia increases the aerosol pH by ~0.9 units. Therefore, China being both more polluted than the USA and richer in ammonia explains the aerosol pH difference. The difference in aerosol acidity highlighted in the present study implies potential differences in formation mechanisms, physicochemical properties, and toxicity of aerosol particles in these two countries.

Understanding the sources and spatiotemporal characteristics of VOCs in the Chengdu Plain, China, through measurement and emission inventory.

In order to evaluate the volatile organic compounds (VOCs) pollution characteristics in Chengdu and to identify their sources, ambient air sample collection and measurement were conducted at 28 sampling sites covering all districts/counties of Chengdu from May 2016 to January 2017. Meanwhile, a county-level anthropogenic speciated VOCs emission inventory was established by "bottom-up" method for 2016. Then, a comparison was made between the VOCs emissions, spatial variations, and source structures derived from the measurement and emission inventory. Ambient measurements showed that the annual average mixing ratios of VOCs in Chengdu were 57.54 ppbv (12.36 to 456.04 ppbv), of which mainly dominated by alkanes (38.8%) and OVOCs (22.0%). The ambient VOCs in Chengdu have distinct spatiotemporal characteristics, with a high concentration in January at the middle-northern part of the city and a low concentration in September at the southwestern part. The spatial distribution of VOCs estimated by the emission inventory was in good agreement with ambient measurements. Comparison of individual VOCs emissions indicated that the emissions of non-methane hydrocarbon species agreed within ±100% between the two methods. Both positive matrix factorization (PMF) model results and emission inventory showed that vehicle emissions were the major contributor of anthropogenic VOCs in Chengdu (31% and 37%), followed by solvent utilization (26% and 27%) and industrial processes (23% and 30%). The large discrepancies were found between the relative contribution of combustion sources, and the PMF resolved more contributions (20%) than the emission inventory (6%). Overall, this study demonstrates that measurement results and emission inventory were in a good agreement. However, to improve the reliability of the emission inventory, we suggest significant revision on source profiles of oxygenated volatile organic compounds (OVOCs) and halocarbons, as well as more detailed investigation should be made in terms of energy consumption in household.

[Impact of a Dust Event on the Size Distribution of Metal Elements in Atmospheric Aerosols at a Coastal Region and over the Ocean].

Size-segregated aerosol samples were collected in the Qingdao coastal region and over the East Sea and the Pacific Northwest from March to April in 2016, and the concentration of metal elements (Al, Na, Fe, Mg, K, Cu, Pb, and Cd) were analyzed. The characteristics and the variation in the size distribution of the metal elements in the samples during dusty weather were discussed, as well as the sources and factors that influence the metals. The results indicated that the concentration of Al, Fe, K, Na, Cu, and Pb in the aerosols in the Qingdao coastal samples increased significantly by 85%-1400%, while the concentration of Cd decreased by 8%; the concentrations of Al, Fe, K, Cu, Pb, and Cd in the samples over the ocean increased by 163%-4580%, while the concentration of Na decreased by 62% during dusty weather. In addition, the size distribution of K changed from a double-peak to a coarse peak mode; that of Pb and Cd changed from a fine peak mode to a double-peak distribution. Cu still presented a double-peak distribution in which the proportion of coarse particles increased; Al, Fe, Mg, and Na showed little variation in their size distribution with a single peak in coarse mode. The dust event had different effects on the size distributions of the metal elements in the coastal and marine aerosol samples. The size distribution of the metal elements (Al, Fe, Mg, Na, and K) in the aerosols collected at the Qingdao coastal site had one peak of 2.1-3.3 µm during dusty weather; the peak moved to 3.3-4.7 µm for marine samples. In addition, the proportion of Al, Fe, Mg, Na, K, Pb, and Cd in the coarse mode decreased by 1%-35% for dust aerosol samples collected in Qingdao coastal region, whereas the proportion of these metals in coarse mode increased by 4%-33% for samples collected over the East Sea. This difference may be related to the hygroscopic growth, transport path, and height of the dust.