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SubseasonalcharacteristicsandthemeteorologicalcausesofsurfaceO3indifferentEastAsiansummermonsoonperiodsovertheNorthChinaPlainduring-

Abstract

Inrecentyears,surfaceozone(O3)hasincreasedrapidlyovertheNorthChinaPlain(NCP),whichisharmfultohumanhealthandcropyields.SummertimeO3overtheNCPisremarkablyinfluencedbytheEastAsiansummermonsoon(EASM),whilethedistinctionsoftheirrelationsindifferentmonsoonperiodsarestillvague.Inthisstudy,wedividedthewholemonsoonseasonintothepre-floodperiod,theMeiyufloodperiod,andthepost-floodperiod.Foreachmonsoonperiod,weexaminedthecharacteristicsandvariationsofO3fromtoandtheassociatedatmosphericcirculationsindividually.Basedonamultiplelinearregressionmodel,wefurtherquantifiedthemeteorologicalcontributionstotheyear-by-yearvariationandincreasingtrendinO3duringdifferentmonsoonperiods.Wefoundthatthemaximumdaily8h-averageO3concentration(O3_MDA8)exhibitssubseasonalvariationsonthemeanlevel(72.5,76.7,and63.8ppb)andtrends(3.2,4.0,and1.7ppbyr-1)duringthethreemonsoonperiods.Meteorologicalvariationsaccountfor58.9%and58.6%oftheO3uptrendsintheMeiyufloodandthepre-floodperiodsbutexertadverseeffectsontheO3increaseinthepost-floodperiod(-27.4%).Thepositivemeteorology-driventrendinthepre-floodperiodisattributedtoincreasedradiationandtemperature,andthatintheMeiyufloodperiodiscontributedbytherisesinradiationandrelativehumidity.Whileinthepost-floodperiod,thedecreasingtrendmainlyresultsfromtheincreasedprecipitation.Thesubseasonaldiscrepancyisrelatedtothedistinctdominanceofwaveactivitiesinthemid-and-highlatitudesandthewesternPacificsubtropicalhigh(WPSH)indifferentmonsoonperiods.Theanomalouslyhighpressureconducestothehigh-levelO3overtheNCPinthepre-floodperiod.FrequentO3pollutionintheMeiyufloodperiodiscausedbythestrongwaveamplitudesinthemid-and-highlatitudesandawestwardstretchedandintensifiedWPSH.Whileinthepost-floodperiod,theeast-westshiftofWPSHmodulatestheprecipitationandO3variationsovertheNCPregion.Amongthethreeperiods,wehighlightedtheMeiyufloodperiodforthehighestO3levelandthemostdrasticincreasingtrend,duringwhichmorestrictemissioncontrolshouldbeimplemented.

Reference

Gao,L.,Wang,T.,Ren,X.,Ma,D.,Zhuang,B.,Li,S.,Xie,M.,Li,M.,andYang,X.-Q.:SubseasonalcharacteristicsandthemeteorologicalcausesofsurfaceO3indifferentEastAsiansummermonsoonperiodsovertheNorthChinaPlainduring-,AtmosphericEnvironment,,