| Atmospheric oxidizing capacity(AOC)determine the removal rates of most primary pollutants and the production rates of secondary pollutants.Understanding of the AOC and radical chemistry are the key point to regional secondary pollution and global climate change.Rapidly growing economies and high population density cause severe photochemical pollution and strong AOC in East China,especily in Jing-Jin-Ji、Yangtze River Delta and Pearl River Delta.Therefore,in order to comprehensively understand the AOC in North and South China background atmosphere,intensive field campaign were carried out at Hok Tsui and Dongying.O3,CO,NOx,HONO,SO2,PAN,VOC,OVOCs and meteorological parameters were simultaneously measured.Also photochemical model,cluster analysis of backward trajectories and weighted potential source contribution function based on the HYSPLIT model were used.Our research find out the pollution characteristic,space-time variation characteristic,atmospheric oxidizing capacity and radical chemistry in North and South China background atmosphere.Level of O3,CO,NOx in Sourth China background atmosphere were higher than other abroad rural sites,especially secondary pollutants like O3 and PAN.A clear seasonal pattern with stronger intensity in late summer compared to autumn and winter was showed.At the end of summer,extremely high level of 03 was oserved at 160 ppbv.In autumn,high level of trace gas would last for a long time.While in winter,most pullutants were much lower expect some long-lived trace gas like CO.Ddiurnal variations also showed apparent seasonal pattern.In late summer,due to the effect of urban plume from Pearl River Delta,diurnal amplitude was more tempestuously.Whlie in antumn and winter,the site was influenced by long scale transported airmass,diurnal amplitude were stable.In contrast,primary and secondary pollutants in North China background atmosphere were higher than that in South China background atmosphere.Primary trace gas like NOx、CO、SO2 and HONO in winter were higher than that in summer while secondary pollutant like O3 in winter was lower than summer.What is different with South China background atmosphere is that diurnal variation in summer and winter were basically the same.Primary trace gas were drop off after sunrise,O3 gradually increase and peaked at noon.So North and South China background atmosphere were both suffered severe photochemical pullution,especily North China background atmosphere.We also find out that peak of AOC in North China background atmosphere was up to 2.1×108 molecules cm-3 s-1,1.5 times than South China background atmosphere.Such high level of AOC was higher than some abroad rural sites and even some megacity sites.OH was the major contributer to daytime AOC in South and North China background atmosphere,followed by NO3 in South China background atmosphere while O3 in North China background atmosphere.In South China background atmosphere,reactions with NO2 dominated the OH loss in summer,while reactions with CO made larger contributions in autumn and winter.During the whole year,OVOCs also play a important role.In North China background atmosphere,reactions with OVOCs dominated the OH loss both in summer and winter.Overall,OVOCs play a significant role in East China background atmosphere,especialy in North China.Primary source of ROx radicals were analysized,results show that photolysis of O3 presented the major ROx source in South China background atmosphere,followed by HONO,HCHO and OVOCs photolysis.The second largest ROx source was HONO photolysis in summer compared to HCHO photolysis in autumn and winter.In North China background atmosphere,HONO photolysis presented the major ROx source in summer,followed by photolysis of HCHO and OVOCs.OVOCs photolysis was the major ROx source in winter,followed by photolysis of HCHO.Cycling rate in North China background atmosphere were several times than South China,while the remove rate were lower,imply more complex chemistry mechanism in North China background atmosphere. |
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