The atmospheric PM 2.5 , PM 2.5 /PM 10 , PCDD/Fs-WHO 2005 -TEQ, and PCDD/F (polychlorinated dibenzo-p-dioxins and dibenzofuran) phase distributions of 23 cities in southern China, during 2014-2016, were investigated in this study. In general, the cities with higher latitudes had higher PM 2.5 concentrations than those with lower latitudes. During 2014-2016, the lowest three-year average concentrations of PM 2.5 occurred at Sanya and Haikou and were 16.4 and 21.7 µg m -3 , respectively; while the highest concentrations of PM 2.5 was occurred at Wuhan and Luzhou and were 68.8 and 63.1 µg m -3 , respectively. During 2015-2016, the PM 2.5 concentrations of most of cities decreased, but those of five cities (Chengdu, Luzhou, Nanchang, Qujing and Quanzhou) increased, indicting that the air quality of these five cities was still not well controlled. The average R M values of the 23 cities were 5.20, 4.49 and 4.13 in 2014, 2015 and 2016, respectively, which revealed that the PM 2.5 concentrations in the cities of southern China slowly decreased, although they were still far above the WHO air quality regulated standard (10 µg m -3). In general, a city with a higher PM 2.5 concentration was also had a higher PM 2.5 /PM 10 ratio. Among the 23 cities, the six highest three-year averages of total-PCDD/Fs-WHO 2005 -TEQ concentrations were 0.0665, 0.0633, 0.0625, 0.0600, 0.0528 and 0.0526 pg-WHO 2005 -TEQ m -3 in Chengdu, Wuhan, Nanjing, Hefei, Luzhou and Hangzhou, respectively. During 2014, the six cities (Hefei, Nanjing, Wuhan, Guiyang, Shanghai and Chengdu) with the lowest temperatures in winter (an average of 5.4°C), their average particle phase fractions of total-PCDD/Fs-WHO 2005 -TEQ that were approximately 76%, 53%, 71% and 93% in the spring, summer, fall and winter, respectively; while, the six cities (Haikou, Fuzhou, Guangzhou, Nanning, Nanchang and Changsha) with the highest temperatures in summer (an average of 16.5°C), had average particle phase fractions of total-PCDD/Fs-WHO 2005 -TEQ that were approximately 61%, 42%, 57% and 81% in the spring, summer, fall and winter, respectively. The results of this study provide information showing the trends of both atmospheric PM 2.5 and PCDD/Fs in the cities of southern China. In addition, this study provided the overview relating to the PM 2.5 and PCDD/Fs in ambient air of southern China, which was not reported in previous studies. The results of this study were of great importance to present the trends of air quality in China. It is also useful for the establishment of control strategies in the future.

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During 2014During -2016, this study investigated the atmospheric PM 2.5 , R M , PM 2.5 /PM 10 , PCDD/Fs-WHO 2005 -TEQ, and PM 2.5 -bound total-PCDD/Fs-WHO 2005 -TEQ content of 22 cities in northern China. In general, the more highly industrialized cities had higher PM 2.5 concentrations. The lowest three-year average concentrations of PM 2.5 occurred at Lhasa and Qiqihar, and were 25.2 and 36.7 µg m -3 , respectively, while the highest concentrations of PM 2.5 occurred at Baoding and Shijiazhuang, and were 106 and 102 µg m -3 , respectively. From 2015 to 2016, the PM 2.5 concentrations of most cities decreased, but those of several others (Shijiazhuang, Taiyuan, Yinchuan, Lhasa, Sinning, Urumqi, Weinan and Xian) increased, suggesting that the air quality of these was still not well controlled. The average of R M values of the 22 cities were 7.2, 6.5, and 6.1 in 2014, 2015 and 2016, respectively, which means the PM 2.5 concentrations in northern China were much higher than the WHO air quality regulated standard (10 µg m -3 ). A city with a higher PM 2.5 concentration always had a higher PM 2.5 /PM 10 ratio. Among the 22 cities, the six highest three-year averages of total-PCDD/Fs-WHO 2005 . The PM 2.5 concentrations, R M values and PCDD/Fs-WHO 2005 -TEQ concentrations in the cities of northern China are higher than those in the south, indicating that the air quality in the north is worse than in the south. The results of this study provide a theoretical basis for proposing air pollution control strategies and improving the atmospheric environment in China.

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Atmospheric deposition is an important pathway for air pollutants entering the environment. In order to better understand both dry and wet deposition of PCDD/Fs in ambient air, two cities -Guangzhou and Nanjing in Southern China, were investigated.