PM_2.5 And Simulated Polychlorinated Dibenzo-p-dioxins And Dibenzofurans?PCDD/Fs? In The Ambient Air Of Major Chinese Northern Cities

Polychlorinated dibenzo-p-dioxins and dibenzofurans?PCDD/Fs?are groups of persistent organic pollutants?POPs?that are widely distributed in the environment,which means they are stable,accumulate easily in the fatty tissue of living organisms and show high toxicity at very low levels.PM_2.5 refer to those particulate matters whose aerodynamic diameter less than 2.5?m.Due to the characters of small siza,large specific surface area and wide range of sources,they are harmful to human and other mammals.In addition,this sort of matters are excellent carrier of POPs like PCDD/Fs.In this work,21 northern cities in China were investigated.PM_2.5 concentration datas during 2015²017 were collected,valid models got from previous studies were used to simulate the gas-particulate distribution and dry-wet deposition process of PCDD/Fs.In this way,the circumstance of air pollution in northern China can be roughly estimated.According to the results,in 21northern cities,the mass concentration of PM_2.5 was higher in spring and winter than summer and fall.Beijing-Tianjin-Hebei region is pollutanted seriously among the northern part of China.Although the annual PM_2.5concentration still above the Chinese and WHO standard,it still showed an obvious decrease during 2015-2017.The result of correlation analyze showed that PM_2.5 and PM₁₀in northern China may had similar sources.The distribution of simulated PCDD/Fs and TEQ had seasonal variation that the concentration was higher in spring and winter than in summer and autumn.The seriously pollutanted area is similar to the seriously pollutanted area of PM_2.5,which is Beijing-Tianjin-Hebei region.During 2015²017,PCDD/Fs and TEQ concentration showed a decrease,while they still higher than the concentration in some parts of the world which were illustrated in other papers.The particulate fraction decerased before increasing.One possible reason is that the gas-particulate fraction of SVOCs like PCDD/Fs is influenced by ambient temperature,the fraction of compounds distribute in the particulate matters increases with increasing of temperature.Moreover,the fraction of particulate increases with increasing of number of chlorine in the compound.Simulated the dry-wet deposition process of PCDD/Fs and TEQ in the ambient air ofBeijing,Shijiazhuang and Harbin,the results showed that dry deposition flux was highest in the winter and fall and lowest in the spring and summer.As for wet deposition flux,it was higher in summer than spring due to the differences between the rainfall.Simulated and estimated the total deposition process of dry and wet deposition,it could be seen from the results that dry deposition was the major pathway of the removal of PCDD/Fs and TEQ in the ambient air.It could be an efficitive way to control the particulate matters emission when controlling the the total deposition of PCDD/Fs and TEQ.