| PM1 and PM2.5 samples were collected in August,November and December 2020 and April 2021 in Zhengzhou to study the composition characteristics of PM1 and PM2.5 and their effects on aerosol pH and visibility.Analysis of chemical composition characteristics based on characteristic ratios(PM 1/PM2.5,NO3-/SO42-,OC/EC,SOC/OC).The transport paths of the winter air mass and the potential sources of PM1 and PM2.5 and their main components were investigated by hybrid single particle lagrangian integrated trajectory(HYSPLIT)model and potential source contribution factor(PSCF)method,respectively.The pH of PM1 and PM2.5 was calculated by thermodynamic model(ISORROPIA-Ⅱ),and the sensitivity of pH to chemical components was studied.The effect of pH on the gas-solid distribution ε(NO3-)andε(NH4+)of gaseous and particulate nitric acid and ammonia was discussed.Moreover,the contribution of the components to the total extinction coefficient(bext)was calculated using the IMPROVE formula.The main conclusions are as follows:(1)The mean values of PM2.5 and PM1 during the sampling period were 71.9 and 56.2 μg·m-3.respectively,and the average value of PM1/PM2.5 was 0.8,It showed that the sub-micron level particulate matter pollution in Zhengzhou was serious.The mean NO3-/SO42-in PM1 was lower than that in PM2.5,indicating that the contribution of mobile sources to PM2.5 was more significant.The mean OC/EC in PM1 was higher than PM2.5,indicating that coal combustion and biomass combustion contributed more to PM1 than PM2.5.SOC accounted for 40%and 50%of the OC concentration in PM1 and PM2.5,respectively,indicating that SOC contributes more to OC in PM2.5.Watersoluble inorganic ions are the most abundant components in PM1 and PM2.5.The concentration of PM1 and PM2.5 was greatly affected by long-distance transmission in the northwest of Zhengzhou by backward trajectory model.The potential source areas of PM2.5,PM1 and their main chemical components in winter are similar by PSCF method,concentrated in Henan Province.(2)Both PM2.5 and PM1 pH were moderately acidic(4.1±1.0).The seasonal change order of aerosol pH was winter(5.4±0.6,5.3±0.4)>autumn(4.0±0.4,4.2±0.4)>spring(4.0±0.3,4.0±0.4)>summer(2.8±0.4,2.9±0.7).Meanwhile,With the aggravation of pollution,the variation in pH value became smaller,Aerosol pH increases with increasing concentration of TNH3 and Ca2+,and decreases with increasing level of SO42-,TNO3,temperature and relative humidity.The result showed that ε(NH4+)raises with decreasing pH,and total ammonia moves to the granular state.ε(NO3-)reduces with decreasing pH,and the total nitric acid moves towards the gaseous state.(3)PM1 has a greater impact on visibility,which reduces with increasing particle concentration.The seasonal order of extinction coefficient was winter(492.0 Mm1)>autumn(416.8 Mm-1)>spring(306.0 Mm-1)>summer(245.1 Mm-1).the extinction contribution was expressed as nitrate(48.1%)>organic matter(28.9%)>sulfate(16.2%)>EC(4%)during the sampling period,because SO2 has a better emission reduction effect,and nitrate gradually exceeds SO42-in terms of mass concentration and relative contribution rate.The extinction contribution of SNA reached 64.3%.From the characteristics of pollution changes,The variation order of extinction coefficient under different pollution conditions was moderate pollution days(792.7 Mm-1)>mild pollution days(355.8 Mm-1)>clean days(264.5 Mm-1),The extinction contribution of nitrate continued to increase during pollution. |
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