Seasonal Characteristics Of Reactive Oxygen Species In Fine Particulate Matter At Atmospheric Background Station In The Yangtze River Delta (Lin'an)

The role of particulate matter(PM)in causing adverse health effects on the human body has been confirmed by many studies,because its redox components cause excessive production of reactive oxygen species(ROS)in situ in the human body.In order to explore the oxidation potential(OP)of the water-soluble components of PM_2.5 and PM₁ in the background area of the Yangtze River Delta,we collected PM_2.5 and PM₁ in Lin'an from July 14 to August 31,2018(summer),from January 2 to February 28,2019(winter).The optical properties and reactive oxygen species(DTT,AA and·OH)in particulate matter samples were analyzed.The results showed that WSOC(water-soluble organic carbon)and mass concentration had similar seasonal characteristics,and both showed a trend that winter is greater than summer.The light absorption of particulate matter samples in Lin'an Regional Atmospheric Background Station had a significant decreasing trend with the increase of wavelength.The light absorption of particulate matter in winter was higher than that in summer.Through parallel factor analysis,two humus-like chromophores(C1,C2)and one protein-like chromophore(C3)were identified in WSOC.The increase in the proportion of C2 in PM_2.5 in winter indicates that unsaturated carbon materials are more likely to be generated in winter.C3 has obvious seasonal characteristics,and it accounts for more than 20%of the particulate matter in summer,which is much higher than that in winter.The average activity levels of PM_2.5 DTT,AA and·OH in Lin'an Regional Atmospheric Background Station in winter and summer were as follows,summer:OP^DTTv,0.71 nmol·min^-1·m^-3;OP^AAv,0.37 nmol·min^-1·m^-3;OP^·OHv,2.41 ng·h·m^-3;winter:OP^DTTv,1.24 nmol·min^-1·m^-3;OP^AAv,0.32 nmol·min^-1·m^-3;OP^·OHv,3.42 ng·h·m^-3.As a site of atmospheric background values in the Yangtze River Delta,compared with European and American countries,the concentration of particulate matter and OP values in Lin'an Regional Atmospheric Background Station were still at a high level of exposure.The OP^DTT and OP^·OH values in winter in Lin'an Regional Atmospheric Background Station were significantly greater than those in summer,while the OP^AA values in summer were slightly greater than those in winter.The values of OP^DTTm,OP^AAmand OP^·OHm in winter were significantly lower than those in summer.PM₁-DTTv accounted for more than 80%of PM_2.5-DTTv value,both PM₁-AAv accounted for PM_2.5-AAv and PM₁-·OHv accounted for more than 60%of PM_2.5-·OHv,which made a great contribution to the oxidation potential of PM_2.5.The mass concentration in Lin'an Regional Atmospheric Background Station had a great influence on the production of·OH free radicals.Winter WSOC,organic substances with light absorption properties and humus-like chromophores were important conditions that affect OP^DTTv.However,these were not important conditions that affect OP^AAv.In addition,humus-like chromophores with lower oxidation degree dominated the OP value of particulate matter in Lin'an Regional Atmospheric Background Station in summer,while in winter,humus-like chromophores with higher oxidation degree dominate the OP value of particulate matter in Lin'an Regional Atmospheric Background Station,and protein-like chromophores had nothing to do with the OP value of particulate matter.Part of the reasons that affect OP^DTT,OP^AA and OP^·OHv values in summer in Lin'an Regional Atmospheric Background Station were similar,due to the effect of photochemical products on OP levels.The backward trajectory analysis showed that the summer air masses in Lin'an Regional Atmospheric Background Station mainly came from the ocean and the transportation of local air masses.Air masses in winter mainly came from cities.Among them,air masses from Shanghai had the greatest impact on air pollution in Lin'an Regional Atmospheric Background Station.