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5 in Baoding were ranked asExpressway less then Secondary roads less then Branch roads less then Major Roads. ③ Further study results of K2.5 characteristics demonstrated that the average K2.5 was higher than 0.15 g·VKT-1 (the value recommended by US EPA) in Baoding City, which would cause an underestimate of road dust emissions and increase the uncertainty of the emissions inventory if the recommended value from the EPA were adopted. The K2.5 in Baoding City is relatively high, indicating that the road dust contains a significant number of micro particles, increasing the contribution of road dust to urban atmospheric PM2.5.The atmosphere is a significant medium for the transportation and diffusion of volatile and semi-volatile pollutants. Furthermore, the atmosphere is the primary exposure route for pollutants to enter the human body. Therefore, the study of the environmental fate of pollutants in the atmosphere is essential. In this study, 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed in snow samples and air samples within 24 hours after a snowfall, and the temporal trend of PAHs in the atmosphere was comprehensively studied. The results indicated that the detection rate of the 16 PAHs in snow was 100%, and the concentration of phenanthrene (538.3 ng·L-1) was the highest, followed by naphthalene (509.1 ng·L-1) and fluoranthene (429.9 ng·L-1), indicating that snowfall can remove PAHs from the atmosphere. After the snowfall, a falling-rising-falling temporal trend of the concentrations of PAHs in the atmosphere was observed. Higher concentrations appeared during rush hour, with the largest automobile exhaust emissions, while lower concentrations appeared during periods with the lowest human activity. The results indicated that the atmospheric concentrations of PAHs were predominantly influenced by human activities. Within 24 hours after snowfall, the ratio of PAHs between the gas phase and particle phase, which depends primarily on the physical and chemical properties of PAHs, had not changed substantially. The diagnostic ratios indicated that within 24 hours after snowfall, the PAHs in the atmosphere originated mostly from the emissions of solid fuel and liquid fuel combustion.In order to reveal the chemical composition characteristics and pollution sources of fine particulate matter (PM2.5) in autumn and winter in Yuncheng, PM2.5 samples were continuously collected using a four-channel small-flow particulate sampler from October 15, 2018 to March 15, 2019. The study prediminantly analyzed the chemical components of water-soluble ions, elemental carbon, organic carbon, and metal elements. Additionally, the chemical mass reconstruction method of particulate matter and the positive matrix factorization model (PMF) were combined for an in-depth discussion. During the sample period, the PM2.5 mass concentrations range was 29.37-370.11 μg·m-3, and 101 days during the sampling period exhibited concentrations that were higher than the secondary standard in China's Ambient Air Quality Standards (GB 3095-2012), with an exceeding rate of 70.63%. These results indicate that the air pollution in Yuncheng in autumn and winter is serious. According to the air quality index (AQI), the collected scal mass reconstruction demonstrate that among the different pollution levels of atmospheric PM2.5 in Yuncheng, the mass percentages of secondary inorganic salt, sea salt, heavy metals, mineral dust, construction dust, organic matter, and elemental carbon were 36%, 2%, 2%, 8%, 1%, 33%, and 5% (clean days), 41%, 1%, 1%, 5%, 0.01%, 31%, and 5% (light-moderate pollution), and 41%, 1%, 1%, 4%, 0.004%, 34%, and 4% (heavy-severe pollution). The proportion of secondary inorganic ions increased and mineral dust decreased with the deterioration of air quality. The PMF analysis results suggest that secondary related sources, coal combustion sources, vehicle exhaust sources, biomass burning, and secondary organic matter are the predominant sources of PM2.5 during serious air pollution in Yuncheng.A six-day ozone pollution episode in Guangzhou in early October 2018 was analyzed with the application of a Lagrangian photochemical trajectory model to trace the sources of ozone, quantify the contributions of different regions, and evaluate the effects of emission reduction measures targeted at different emission sectors and different precursors on ozone pollution. The results showed that during the ozone pollution episode, the maximum daily 8 h ozone exceeded 160 μg·m-3 and the highest value reached 271 μg·m-3. The average concentrations of nitrogen oxides and volatile organic compounds (VOCs) were (77.7±42.8) μg·m-3 and (71.9±56.2) μg·m-3, respectively. Aromatics and alkenes were the dominant reactive VOCs, with contributions of 38% and 30% to·OH reactivity and 51% and 16% to ozone formation potential, respectively. The ozone pollution in Guangzhou during this episode was affected by three types of air masses, with the primary source regions of Guangzhou, Guangdong Province, and regions outside Guangdong Province. For all three air mass types, ozone production in these source region was controlled by VOCs. Sensitivity tests showed that, in the primary source regions, reducing the emissions of VOCs is more effective than reducing NOx in terms of reducing ozone concentrations. Under the condition of full emission reduction, regulating traffic emissions could substantially reduce ozone levels by 14.6%-21.0% in Guangzhou, which was a more significant reduction than regulating controlled industry (8.4%-15.3%), power plant (0.9%-6.2%) and residential (2.3%-4.7%) emissions. However, the traffic emission reduction is not as effective (induced ozone reduction less then 10%) when the emissions reduction ratio is lower than 90%. In addition, biogenic emissions in the Pearl River Delta also substantially contributed to the ozone levels under certain circumstances, as indicated by the ozone reduction up to 19% when biogenic emissions were shut off.Based on the atmospheric pollutant data from twelve monitoring sites in the Guangdong-Hong Kong-Macao Pearl River Delta Regional Air Quality Monitoring Network, the mass concentration trends of atmospheric photochemical oxidants (Ox, NO2+O3) and PM2.5 during 2013-2017 were studied. The complex nonattainment pollution of Ox and PM2.5 is defined as the daily average mass concentration of NO2 and PM2.5 and daily maximum 8 h average (O3 MDA8) mass concentration of O3 simultaneously that exceeds the Chinese grade Ⅱ national air quality standard. The characteristics and meteorological factors that influence the complex nonattainment pollution of Ox and PM2.5 at different types of areas were analyzed. The results indicate that from 2013 to 2017, the annual average mass concentration of PM2.5 in the Pearl River Delta (PRD) region decreased from (44±7) μg·m-3 to (32±4) μg·m-3, which met the annual standard for three consecutive years. learn more The annual average mass concentration of Ox decreased from (127±14) μg·m-3 in 2013 to (114±12) μg·m-3 in 2016 and then showed a general rebound trend to (129±13) μg·m-3 in 2017 when O3 concentrations increased significantly (10 μg·m-3).