2020年和2021年南京城区臭氧生成敏感性和VOCs来源变化分析

Changes in O_(3)-VOCs-NO_(x) Sensitivity and VOCs Sources at an Urban Site of Nanjing Between 2020 and 2021

PM_(2.5)和臭氧(O_(3))协同防控是“十四五”期间空气质量提升的重点.O_(3)生成与其前体物挥发性有机物(VOCs)和氮氧化物(NO_(x))呈高度非线性关系.基于南京市城区站点2020年和2021年的4~9月O_(3)、 VOCs和NO_(x)的连续在线监测数据,比较了两年间O_(3)及其前体物浓度的变化,进一步利用基于观测的盒子模型(OBM)和正定矩阵因子分解(PMF)模型分析了O_(3)-VOCs-NO_(x)敏感性和VOCs来源.结果表明,2021年的4~9月O_(3)日最大浓度、 VOCs和NO_(x)浓度的平均值相较于2020年同期约下降7%(P=0.031)、 17.6%(P<0.001)和14.0%(P=0.004).2020年和2021年的O_(3)超标天NO_(x)和人为源VOCs的平均相对增量反应活性(RIR)分别为0.17和0.14, 0.21和0.14,说明O_(3)生成处于VOCs和NO_(x)协同控制区.基于人为源VOCs和NO_(x)削减情景所模拟的O_(3)生成潜势等值线(EKMA曲线)也支撑这一结论.PMF解析结果显示工业和交通排放是VOCs的主要来源,其中与工业排放相关有5个因子,包括工业液化石油气(LPG)使用、苯化工、石化、甲苯相关的工业和溶剂涂料使用,对总VOCs浓度的贡献率为55%~57%.机动车尾气和汽油挥发因子的贡献率之和为43%~45%.进一步计算各因子的RIR值,结果显示石化和溶剂涂料使用的RIR值最高,说明从臭氧防控的角度,需要优先削减这两类源的VOCs排放.随着VOCs和NO_(x)减排措施的实施,O_(3)敏感性和VOCs来源会改变,因此在“十四五”期间仍需持续关注,以及时调整O_(3)防控策略.

The synergistic control of PM_(2.5) and ozone(O_(3))are the focus of air quality improvement during the 14th Five-Year Plan in China.The production of O_(3) shows a highly nonlinear relationship with its precursors volatile organic compounds(VOCs)and nitrogen oxides(NO_(x)).In this study,we conducted online observations of O_(3),VOCs,and NO_(x) at an urban site in downtown Nanjing from April to September of 2020 and 2021.The average concentrations of O_(3) and its precursors between these two years were compared,and then the O_(3)-VOCs-NO_(x) sensitivity and the VOCs sources were analyzed using the observation-based box model(OBM)and positive matrix factorization(PMF),respectively.The results showed that the mean daily maximum O_(3) concentrations,VOCs,and NO_(x) concentrations decreased by 7%(P=0.031),17.6%(P<0.001),and 14.0%(P=0.004)from April to September of 2021 compared with those from the same period in 2020,respectively.The average relative incremental reactivity(RIR)values of NO_(x) and anthropogenic VOCs during the O_(3) non-attainment days in 2020 and 2021 were 0.17 and 0.14 and 0.21 and 0.14,respectively.The positive RIR values of NO_(x) and VOCs indicated that O_(3) production was controlled by both VOCs and NO_(x).The O_(3) production potential contours(EKMA curves)based on the 50×50 scenario simulations also supported this conclusion.The PMF results showed that industrial and traffic-related emissions were the main sources of VOCs.The five PMF-resolved factors were identified as industrial emissions,including industrial liquefied petroleum gas(LPG)use,the benzene-related industry,petrochemistry,toluene-related industry,and solvent and paint use,which contributed 55%-57%of the average mass concentration of total VOCs.The summed relative contributions of vehicular exhaust and gasoline evaporation were 43%-45%.Petrochemistry and solvent and paint use showed the two highest RIR values,suggesting that VOCs from these two sources should be reduced with priority to control O_(3).With the implementation of VOCs and NO_(x) control measures,the O_(3)-VOCs-NO_(x) sensitivity and VOCs sources have changed,and therefore we still need to follow their variations in the future to timely adjust O_(3) control strategies during the 14th Five-Year Plan.