ABSTRACT
The effects of 9 precipitation events in Suzhou City in Anhui Province, China, on the air quality index (AQI), PM2.5, and dry deposition flux of PCDD/Fs (polydibenzo-p-dioxins and polydibenzofurans) were investigated. A total of 7 precipitation events were positive contributes to the reduction of AQI;among them, the AQI were between 23 and 216, with an average of 75, the PM2.5 concentrations were between 5.0 and 169 mu g m-3, with an average of 25 mu g m-3, while the total-PCDD/F-TEQ dry deposition flux ranged from 149 to 1034 pg WHO2005-TEQ m-2 day-1 and averaged 315 pg WHO2005-TEQ m-2 day-1. By comparing the average AQI and PM2.5, respectively, during and after rainfall with that before rainfall, the results indicated that the average reduction fractions of AQI were 26% and 44%, respectively, while those of PM2.5 were 58% and 43%. In addition, the effect of precipitation on the average reduction fraction of total PCDD/F-TEQ dry deposition flux was 31%. However, in the other 2 AQI elevation events, the AQI were between 23 and 100, and averaged 51;when comparing the average AQI and PM2.5 concentrations, during and after the rain with that before the rain, the increases in AQI were 42% and 49%, respectively, while the increases in PM2.5 concentration were 26% and 29%, respectively. The above results show that, on the whole, rain and snow improved the air quality. This is because rainwater removes particles or dissolved gaseous pollutants from the atmosphere and brings aerosols to the ground. However, in some cases, the increase of source emissions and atmospheric vertical convection, the effect of precipitation or air humidity increased the AQI and elevated the concentration of PM2.5, and dry deposition flux of PCDD/Fs. The results of this study provide useful information for both scientific communities and air quality management.
ABSTRACT
This study mainly involved conducting an atmospheric sensitivity analysis of the dry deposition and PM2.5-bound content of total PCDD/Fs-WHO2005-TEQ, respectively. The results for Fuzhou and Xiamen cities showed that the total PCDD/F mass concentration was the factor most positively correlated to the dry deposition flux: When Delta P/P ranged from -50% to 0%, Delta S/S ranged from -66.0% to 0%, but when Delta P/P increased from 0% to +50%, Delta S/S increased from 0% to +66.0%, respectively. The second factor positively correlated with the deposition flux was the PM2.5 concentration: When Delta P/P ranged from -50% to 0%, Delta S/S ranged from -63.3% to 0%;when Delta P/P increased from 0% to +50% and +100%, Delta S/S ranged from 0% to +20.8 and -0.9%, respectively. Ambient air temperature was found to be less sensitive to dry deposition fluxes in total PCDD/Fs-WHO2005-TEQ: When Delta P/P ranged from -50% to -17% and 0%, Delta S/S ranged from -17.0% to +5.6% and 0%;when Delta P/P increased from 0% to +50%, Delta S/S increased from 0% to -84.5%, respectively. The sensitivity analysis for PM2.5-bound total PCDD/Fs-WHO2005-TEQ content had similar results to those for dry deposition flux. In addition, in 2018, 2019, and 2020, the annual average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content at Fuzhou and Xiamen was 0.430, 0.127, 0.303, and 0.426 ng-WHO2005-TEQ g(-1) in the spring, summer, autumn and winter, respectively, which showed that summer had the lowest content, while spring and winter had the highest. The results of this study provided useful information for gaining a deeper understanding of both dry deposition and particle-bound of PCDD/Fs in the ambient air.
ABSTRACT
In this study, the atmospheric total-PCDD/Fs-WHO2005-TEQ concentrations, gas-particle partitioning, PM2.5 concentration, PM2.5-bound total PCDD/Fs-WHO2005-TEQ content and dry deposition flux in Shanghai and Nanjing were investigated from 2018-2020. In Shanghai, the total PCDD/Fs-WHO2005-TEQ concentration dropped from 0.0291 pg-WHO2005-TEQ m–3 from 2018–2019 to 0.0250 pg-WHO2005-TEQ m–3 in 2020, while in Nanjing, it dropped from 0.0423 pg-WHO2005-TEQ m–3 to 0.0338 pg-WHO2005-TEQ m–3. The average concentrations of PCDD/Fs-WHO2005-TEQ in spring and winter in Shanghai and Nanjing were 47.6% and 53.8% higher than those in summer, respectively. From 2018-2019, the average particle phase fractions of total-PCDD/Fs-WHO2005-TEQ in Shanghai and Nanjing were 50.3% and 57.5%, respectively, while in 2020, they were 47.8% and 55.1%, respectively. From 2018-2019, the average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content was 0.342 and 0.493 ng-WHO2005-TEQ g–1 in Shanghai and Nanjing, respectively, while in 2020, it was 0.312 and 0.489 ng-WHO2005-TEQ g–1, respectively. In Shanghai and Nanjing, the average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content in spring and winter was 77.5% and 73.2% higher than that in summer, respectively. From 2018–2019, the dry deposition flux of total-PCDD/Fs-WHO2005-TEQ was 316.3 and 460.5 pg WHO2005-TEQ m–2 month–1 in Shanghai and Nanjing, respectively, while in 2020, it was 272.5 and 368.4 pg WHO2005-TEQ m–2 month–1, respectively. The average dry deposition flux of total-PCDD/Fs-WHO2005-TEQ in spring and winter was 47.6% and 53.8% higher than that summer in Shanghai and Nanjing, respectively. The above results indicate that COVID-19 in 2020 had a positive effect on air quality improvement in PCDD/Fs. On average, more than 98.88% of the total PCDD/Fs-WHO2005-TEQ dry deposition flux was primarily contributed by the particle phase. This was attributed to the fact that dry deposition of particle phase PCDD/Fs was mainly due to gravitational settling accompanied by higher dry deposition velocities, while the gas phase PCDD/Fs were deposited mostly by diffusion at a lower dry deposition velocity. © The Author(s).