Vertical Distribution Characteristics of Lower Troposphere VOCs and Its Potential Effect on Ozone Formation in the Northern Suburb of Nanjing City,Jiangsu Province,China
Ozone pollution shows a trend of increasing,but the potential contribution of volatile organic compounds(VOCs)to ozone formation in the vertical direction is still unclear.The vertical distribution characteristics of VOCs and its impact on ozone formation were studied based the enhanced sounding data in the lower troposphere(0-1 000 m)from October 17 to November 15,2020 observed in the northern suburbs of Nanjing city,Jiangsu province.The results show that ① the volume fraction of VOCs((73.4±26.1)×10-9-(50.4±20.3)×10-9)decreases with the increase of height,and alkanes account for the largest proportion(64.3%-71.6%)at each height,and the proportion of olefin(3.4%-9.9%)gradually decrease with the increase of height;there is no significant change in the proportion of aromatics,halohydrocarbons and acetylene;the VOCs accumulate in the lower layer in the morning and evening with a great gradient,and the proportion of alkane increases due to the traffic emissions and lower boundary layer;the VOCs profiles are uniform in the afternoon.② Affected by atmospheric junction,the alkanes and olefin dominate the photochemical reactions in the mixing layer,with the loss rate of OH radicals(LOH)of 3.3 and 2.7 s-1,accounting for 42.8%and 35.1%,respectively;alkanes and aromatics are the dominant species in the stable boundary layer and residual layer.③ The LOH and ozone formation potential(OFP)of VOCs in the afternoon mixing layer are positively correlated with the ozone volume fraction,which represent the relationship between local VOCs and ozone;however,there is no significant correlation between LOH,OFP and ozone in the stable boundary layer and residual layer in the morning;the contributions of VOCs components with high reaction activity to OFP are occurred in the low layer,and ethene and propene are the representative components;alkane makes greater contribution to the photochemical generation of ozone in the upper atmosphere,and the analysis result of X/E ratio reflects higher aging and the characteristics of regional atmospheric.Limiting chemical plant emissions,and improving vehicle emission standards and fuel quality,are the key to improve ozone pollution in Nanjing.
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