Photochemical smog characterized by high concentrations of ozone(O_(3)) is a serious air pollution issue in the North China Plain(NCP)region,especially in summer and autumn.For this study,measurements of O_(3),nitroge...Photochemical smog characterized by high concentrations of ozone(O_(3)) is a serious air pollution issue in the North China Plain(NCP)region,especially in summer and autumn.For this study,measurements of O_(3),nitrogen oxides(NO_(x)),volatile organic compounds(VOCs),carbon monoxide(CO),nitrous acid(HONO),and a number of key physical parameters were taken at a suburban site,Xianghe,in the NCP region during the summer of 2018 in order to better understand the photochemical processes leading to O_(3)formation and find an optimal way to control O_(3)pollution.Here,the radical chemistry and O_(3)photochemical budget based on measurement data from 1−23 July using a chemical box model is investigated.The daytime(0600−1800 LST)average production rate of the primary radicals referred to as RO_(x)(OH+HO2+RO2)is 3.9 ppbv h−1.HONO photolysis is the largest primary RO_(x)source(41%).Reaction of NO2+OH is the largest contributor to radical termination(41%),followed by reactions of RO2+NO2(26%).The average diurnal maximum O_(3)production and loss rates are 32.9 ppbv h−1 and 4.3 ppbv h−1,respectively.Sensitivity tests without the HONO constraint lead to decreases in daytime average primary RO_(x)production by 55%and O_(3)photochemical production by 42%,highlighting the importance of accurate HONO measurements when quantifying the RO_(x)budget and O_(3)photochemical production.Considering heterogeneous reactions of trace gases and radicals on aerosols,aerosol uptake of HO2 contributes 11%to RO_(x)sink,and the daytime average O_(3)photochemical production decreases by 14%.The O_(3)-NO_(x)-VOCs sensitivity shows that the O_(3)production at Xianghe during the investigation period is mainly controlled by VOCs.展开更多
准确识别和定量挥发性有机化合物(volatile organic compounds,VOCs)氧化中间产物(包括闭壳产物和有机过氧自由基RO_(2)),对于厘清其降解机理和实现二次物种精准模拟与精细化管控十分关键.本研究基于最新开发的质子转移反应-飞行时间质...准确识别和定量挥发性有机化合物(volatile organic compounds,VOCs)氧化中间产物(包括闭壳产物和有机过氧自由基RO_(2)),对于厘清其降解机理和实现二次物种精准模拟与精细化管控十分关键.本研究基于最新开发的质子转移反应-飞行时间质谱,结合高选择性的铵根离子加成模式,发展了铵根-电离质谱法(ammonium chemical ionization mass spectrometry,NH_(4)^(+)-CIMS),成功实现了对不同种类的RO_(2)自由基以及含氧VOCs物种的高灵敏度检测.通过自主搭建的标定系统,实现了基于质谱法测量RO_(2)自由基的直接标定,有效降低了由于灵敏度替代造成的测量不确定性.该套系统首先应用于近实际大气条件下α-蒎烯臭氧氧化体系的研究,共检测到13种一代反应产物,包括5种RO_(2)自由基和8种闭壳物种,其中来自OH氧化反应生成的过氧自由基C_(10)H_(17)O_(3)占比最大,臭氧氧化α-蒎烯生成的过氧自由基C_(10)H_(15)O_(4)发生多步自氧化及双分子反应,生成含更高氧数的过氧自由基和闭壳产物,证实了α-蒎烯自氧化反应通道的重要性.现有大气化学机理可基本捕捉α-蒎烯臭氧化反应的产物分布,但不同氧化通道产物的相对占比受模型设置的反应速率和反应通道分支比影响存在较大不确定性.此外,氢摘取通道可能对OH自由基氧化α-蒎烯具有重要贡献,但机制待进一步探索.本研究展示的NH_(4)^(+)化学电离质谱技术,具有高灵敏度、高分辨率、低检测限等优点,特别是对中等氧化程度的闭壳产物和RO_(2)自由基的检测.未来,这套系统有望在更复杂的大气环境中揭示VOCs的演化规律和降解机制,为大气环境保护提供重要科学依据.展开更多
基金This work was supported by grants from the National Key Research and Development Program of China(Grant No.2017YFC0210003).
文摘Photochemical smog characterized by high concentrations of ozone(O_(3)) is a serious air pollution issue in the North China Plain(NCP)region,especially in summer and autumn.For this study,measurements of O_(3),nitrogen oxides(NO_(x)),volatile organic compounds(VOCs),carbon monoxide(CO),nitrous acid(HONO),and a number of key physical parameters were taken at a suburban site,Xianghe,in the NCP region during the summer of 2018 in order to better understand the photochemical processes leading to O_(3)formation and find an optimal way to control O_(3)pollution.Here,the radical chemistry and O_(3)photochemical budget based on measurement data from 1−23 July using a chemical box model is investigated.The daytime(0600−1800 LST)average production rate of the primary radicals referred to as RO_(x)(OH+HO2+RO2)is 3.9 ppbv h−1.HONO photolysis is the largest primary RO_(x)source(41%).Reaction of NO2+OH is the largest contributor to radical termination(41%),followed by reactions of RO2+NO2(26%).The average diurnal maximum O_(3)production and loss rates are 32.9 ppbv h−1 and 4.3 ppbv h−1,respectively.Sensitivity tests without the HONO constraint lead to decreases in daytime average primary RO_(x)production by 55%and O_(3)photochemical production by 42%,highlighting the importance of accurate HONO measurements when quantifying the RO_(x)budget and O_(3)photochemical production.Considering heterogeneous reactions of trace gases and radicals on aerosols,aerosol uptake of HO2 contributes 11%to RO_(x)sink,and the daytime average O_(3)photochemical production decreases by 14%.The O_(3)-NO_(x)-VOCs sensitivity shows that the O_(3)production at Xianghe during the investigation period is mainly controlled by VOCs.
文摘准确识别和定量挥发性有机化合物(volatile organic compounds,VOCs)氧化中间产物(包括闭壳产物和有机过氧自由基RO_(2)),对于厘清其降解机理和实现二次物种精准模拟与精细化管控十分关键.本研究基于最新开发的质子转移反应-飞行时间质谱,结合高选择性的铵根离子加成模式,发展了铵根-电离质谱法(ammonium chemical ionization mass spectrometry,NH_(4)^(+)-CIMS),成功实现了对不同种类的RO_(2)自由基以及含氧VOCs物种的高灵敏度检测.通过自主搭建的标定系统,实现了基于质谱法测量RO_(2)自由基的直接标定,有效降低了由于灵敏度替代造成的测量不确定性.该套系统首先应用于近实际大气条件下α-蒎烯臭氧氧化体系的研究,共检测到13种一代反应产物,包括5种RO_(2)自由基和8种闭壳物种,其中来自OH氧化反应生成的过氧自由基C_(10)H_(17)O_(3)占比最大,臭氧氧化α-蒎烯生成的过氧自由基C_(10)H_(15)O_(4)发生多步自氧化及双分子反应,生成含更高氧数的过氧自由基和闭壳产物,证实了α-蒎烯自氧化反应通道的重要性.现有大气化学机理可基本捕捉α-蒎烯臭氧化反应的产物分布,但不同氧化通道产物的相对占比受模型设置的反应速率和反应通道分支比影响存在较大不确定性.此外,氢摘取通道可能对OH自由基氧化α-蒎烯具有重要贡献,但机制待进一步探索.本研究展示的NH_(4)^(+)化学电离质谱技术,具有高灵敏度、高分辨率、低检测限等优点,特别是对中等氧化程度的闭壳产物和RO_(2)自由基的检测.未来,这套系统有望在更复杂的大气环境中揭示VOCs的演化规律和降解机制,为大气环境保护提供重要科学依据.
