| Continuously monitoring of PM2.5 and ozone concentrations in the air of Shanghai was carried out from May 27,2018 to March 31,2019.During the monitoring period,the PM2.5 concentrations in Shanghai ranged from?6.04 ?g/m3?to?220.74 ?g/m3?,with an average concentration of?39.35±35.74 ?g/m3?.The mass level range of O3-8h was?6.27 ?g/m3?to?252.91 ?g/m3?,and the average value was?86.49±41.65 ?g/m3?.High PM2.5 concentration was found in autumn and winter,while the low PM2.5 concentration was found in spring and in summer.The variation of O3-8h value was different with that of PM2.5,showing high concentration in spring and summer,and low concentration in autumn and winter.Our data showed that the PM2.5 was still the major air pollutant in Shanghai compared with ozone.Cluster analysis data showed that the air masses from the northwest and northern regions carried high concentrations of PM2.5.Cluster statistical results showed that PM2.5 pollution from air masses in the northern region was seasonal,and the sources of pollution were presumed to be industrial emissions and combustion products.Compared with northern China,the seasonality of PM2.5 concentration in northwest China was weaker.It was speculated that the pollution episodes were mainly caused by dust mineral particles and combustion products such as coal combusion.The air mass cluster from the south carried the highest concentration of ozone because it passed through coastal provinces with well-developed traffic and were richer in ozone precursors and sunlight than other regions.The analysis results of PSCF and CWT showed that Shanxi,Gansu,Ningxia Hui Autonomous Region,Inner Mongolia,and northeastern Xinjiang were the main potential sources of PM2.5.Zhejiang Province,Fujian Province,Guangdong Province,and South China Sea were the major potential areas for ozone.Twenty elements?Na,Mg,Al,P,S,Cl,K,Ca,Ti,V,Cr,Mn,Fe,Ni,Cu,Zn,Br,Sr,Ba,Pb?in the PM2.5 samples which were divided by season and source area were analyzed.The high mass level of Ca in PM2.5 samples in summer and autumn might be related to the water accumulation improvement project on Shangda Road during sampling time.According to the concentration of soil dust,there was a higher concentration of soil dust in the northwest than in the north.The average concentration of K in autumn samples was much higher than that in other seasons,which was due to the high emissions of burning fuel such as crop residues and coal in the northeast and northern regions of China,while the air mass arriving in Shanghai at this time was mainly in the north.There was no significant difference in the seasonal variation of S mass concentration,which indicateed that S in Shanghai's atmosphere might not be caused by coal combustion.The average concentrations of trace elements Ti,V,Mn,Fe,Cu,Zn,Sr and Pb were lower than those in previous studies.The concentrations of Mn,Cu,Zn,and Pb reached their maximum in winter.The possible reason was that there were several important industrial parks in the north,and the low wind speed and low temperature in Shanghai in winter might cause poor air diffusion.The ozone concentration in Shanghai was positively correlated with the concentrations of Ba?r = 0.64;p <0.05?and V?r = 0.30;p> 0.05?in PM2.5,and negatively correlated with other chemical elements.As VOCs,Ba and V are all related to vehicle emissions and fossil fuel combustion,this indirectly proved that ozone in Shanghai's atmosphere was a VOC-limited regime.In general,the high levels of ozone in Shanghai's atmosphere were mainly caused by the combined effect of local to regional ozone precursor emissions and trans-regional ozone transmission.The oxidation potential and cytotoxicity of water-soluble PM before and after ozone oxidation were tested by using DTT analysis and MTT analysis,respectively.The changes of oxidation potential and cell mortality were consistent with the increase of ozone exposure time.Within 2 hours of exposure to ozone,the oxidation potential and cell mortality of water-soluble PM changed rapidly,and after 2 hours,they remained almost unchanged.After being oxidized by ozone for 2 hours,the oxidation potential and cell mortality of water-soluble PM increased to 40.9% and 41.4%,respectively. |
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