Research On The Pollution Characteristics And Causes Of PM_2.5 And O₃ In Yuncheng City

In recent years,the air quality problem in Yuncheng City has become increasingly serious,and the pollution of atmospheric particulate matter and ozone is the focus of current attention.Based on the ambient air quality monitoring data,PM_2.5component data,VOCs component data and meteorological data of Yuncheng City from 2018 to 2020,this paper analyzes the pollution characteristics of particulate matter and ozone,and focuses on the effect of atmospheric oxidization on particulate matter.The impact of the heterogeneous chemical reaction of particulate matter on ozone was discussed in detail from the aspects of precursors,pollution periods,meteorological factors,and regional transmission paths,and the causes of the pollution of particulate matter and ozone were obtained.The main conclusions are as follows:（1）The annual variation characteristics of PM_2.5and O₃concentrations in Yuncheng City are:the pollution levels of both increased first and then decreased from 2018 to 2020.The PM_2.5pollution months are mainly January,and the O₃pollution months are mainly June and August.The seasonal variation of PM_2.5concentration is winter>autumn>spring>summer,and the seasonal variation of O₃concentration is completely opposite.The diurnal variation of PM_2.5concentration in winter presents a unimodal distribution,with a peak at 12 noon.The diurnal variation of O₃concentration in winter and summer showed a unimodal distribution,with the peaks appearing at 16:00 and 15:00,respectively.（2）Oxidation of the atmosphere in Yuncheng City is dominated by O₃.In O₃pollution months,PM_2.5was positively correlated with O₃.In PM_2.5polluted months,PM_2.5was negatively correlated with O₃.Due to the strong oxidative properties of the atmosphere in summer,secondary organic aerosols are generated,which in turn promotes the generation of secondary PM_2.5.The generation of secondary PM_2.5increases with the increase of photochemical levels.The effect of O₃on the concentration of secondary PM_2.5is more significant than that of primary PM_2.5.（3）Since the heterogeneous chemical reaction of particulate matter in Yuncheng City and the extinction coefficient of atmospheric aerosols have an impact on the O₃concentration,when the PM_2.5pollution level is below moderate pollution,the O₃concentration will follow the heterogeneous chemical reaction on the surface of the particulate matter.And increased,at this time PM_2.5and O₃were positively correlated.When the concentration of PM_2.5in the atmosphere is high in winter,the mixed absorption aerosol will weaken the photochemical reaction rate of ozone,resulting in a decrease in the concentration of O₃.At this time,PM_2.5is negatively correlated with O₃.（4）The PM_2.5pollution in Yuncheng City is mainly caused by the efficient conversion of secondary ions and the superposition of the formation of secondary organic aerosols.The proportion of water-soluble inorganic ions in PM_2.5is 62.7%,of which SNA accounts for56.93%.The carbonaceous component results showed that the OC was 2 times higher in the heating period than in the non-heating period.The correlation between SOR and RH was higher,and NOR was jointly affected by Ox and RH.The formation process of O₃in summer belongs to the VOCs control area or the VOCs collaborative control area.The main components of VOCs in Yuncheng are OVOCs and alkanes.Acetone,acetaldehyde and propionaldehyde contribute the most to the concentration of OVOCs.OVOCs contributed the most to the formation potential of O₃,followed by alkenes,aromatics,alkanes and alkynes.