Evolution And Cause Of Heavy Pollution In The Atmospheric Boundary Layer Of Shijiazhuang In Summer

In the summer and autumn,there is a phenomenon of“double high" atmospheric combined pollution of ozone(O3)and particulate matter in Shijiazhuang,but the mechanism of its pollution is still unclear.In this study,we conducted a one-month observation(from 15th June to 14th July,2016)of pollutants in Shijiazhuang(37053'N,114°38'E),a severe polluted city in NCP.On the one hand,the online instrument was used to continuously collect the concentration of near-surface O3 and its precursors,and miniaturized ozonesonde was carried on a tethered balloon to obtain the vertical distribution of the O3 concentration.On the other hand,the particulate matter in the actual atmosphere is obtained by a medium-flow air particulate sampler,and the chemical components(water-soluble ions,carbon components and metal elements)in PM2.5 and PMi are quantitatively analyzed by off-line analysis.In addition,we analyzed the main source of particulate matter by PMF.The following main conclusions were drawn.Photochemical pollution in Shijiazhuang is serious in summer,and the O3 concentration exceeded the standard by approximately 60%in this study.High temperatures and southeasterly winds lead to elevated O3 values.At moderate relative humidity(40%-50%)and medium boundary layer heights(1200-1500 m),the O3 concentration was the highest.Further analysis shows that the evolution of the boundary layer makes the O3 generation sensitivity changed.When O3 generation is controlled by NOx and VOCs,the O3 concentration is the highest,and the meteorological conditions correspond to the above.The vertical profiles of O3 were also measured by a tethered balloon.The results showed that a large amount of O3 was stored in the residual layer,and the concentration was positively correlated with the O3 concentration measured the previous day.During the daytime of the following day,the contribution of O3 stored in the residual layer to the boundary layer reached 27%±7%on average.The particulate matter pollution in Shijiazhuang in summer is also serious,and the over-standard rate of PM2.5 is 93%.The chemical components of PMi and PM2.5 are mainly SO42-,NO3-?NH4+ and OM,accounting for 14%,8%?11%?11%to PMi and 13%?8%?10%.9%to PM2.5.The sources of PMi and PM2.5 are similar,mainly secondary nitrate,secondary sulfate,industrial pollution,vehicle emissions,dust,biomass burning and coal combustion.The contribution to PMi is 2g%.30%.10%,9%,8%,8%,6%,respectively.The contribution to PM2.5 is 29%,33%,12%,13%,8%,2%,4%,respectively.According to the analysis of typical pollution period,PMi and PM2.5 increased simultaneously during the explosive growth,but PMi growth was slow in sustained growth,and PM2.5 continued to increase.SNA is the main reason for it.By analyzing the chemical components of different pollution levels,it was found that the main chemical components(carbon components and SNA)in PMi and PM2.5 increased simultaneously during the explosive growth.In the later stage of pollution,the carbon component,nitrate and ammonium salts are less changed,and the sulfate is increased rapidly.Therefore,the prevention and control strategies of PMi and PM2.5 are different.Inorganic gaseous precursors are still the key of PM2.5 prevention in summer,especially SO2.