大气化学机理的发展及应用

大气化学机理是研究大气化学过程的重要手段和方法之一,也是发展空气质量模式必不可少的重要组成部分。作者综述了几种应用广泛的简化机理——碳键机理(Carbon Bond Mechanism,CBM)、加州大气污染研究中心机理(Statewide Air Pollution Research Center mechanism,SAPRC)、区域酸沉降机理(Regional Acid Deposition Mechanism,RADM)、区域大气化学机理(Regional Atmospheric Chemical Mechanism,RACM)以及详细化学机理——主要大气化学机理(Master Chemical Mechanism,MCM)和共同代表性中间体机理(Common Representative Intermediates,CRI)的发展及应用。对上述大气化学机理的产生、发展、包含的物种类型、集总方式等方面进行了对比分析,总结了采用烟雾箱数据评价大气化学机理的研究成果以及大气化学机理在模式发展方面的应用,并对大气化学机理的进一步发展与完善提出了需求。

石化企业周边采暖季大气VOCs污染特征及化学反应活性

采集济南市石化企业周边采暖季环境空气中挥发性有机化合物(volatile organic compounds,VOCs)在线数据,进行了大气VOC成分组成及化学反应活性的分析.结果表明,2017年冬季采暖季期间,石化企业周边VOCs日均质量浓度为(57.82±49.79)μg·m-3,其中烷烃占比最高为61.53%,其次为芳香烃.日均质量浓度前三位的单体的分别是丙烷、乙烷和乙烯.MCM模拟结果表明,特殊污染日O3净生成反应速率为1.01 (μg·m-3)·h-1,HO2+NO和RO2(除CH3O2外)+NO两大反应控制O3生成;而NO2+OH反应控制O3消耗.增量反应活性RIR和臭氧生成潜势OFP计算结果表明∑VOCs和NOx共同控制O3生成,且VOCs中的芳香烃和烯烃对O3的生成影响较大;对二次有机气溶胶生成贡献率最大的VOCs物种是芳香烃类,其贡献率高达94.05%,贡献率最高单体物质是甲苯,其次为乙苯.因此控制芳香烃类VOCs物种排放不仅可以减轻石化企业周边的冬季臭氧污染,同时对济南市的冬季灰霾污染有一定的控制.PMF源解析结果表明工业污染源、汽油挥发源和机动车尾气排放源是石化企业周边采暖季大气中VOCs的主要来源,控制这三类污染源排放是目前治理石化企业周边采暖季VOCs污染的主要途径.

烟雾箱与数值模拟研究苯和乙苯的臭氧生成潜势

结合光化学烟雾箱实验与数值模拟研究了苯和乙苯在NO，存在条件下的光氧化臭氧生成潜势．重复实验表明，在乙苯一NO。反应体系中，反应物初始浓度、温度、湿度和光照强度接近的条件下，整个反应过程中臭氧的最大偏差仅为4％，证明了烟雾箱的可重复性较高．在烟雾箱实验的基础上，使用MCM（masterchemicalmechanism）模拟了苯和乙苯的光氧化03生成，并将其结果与实验数据进行了比对分析．干燥（≤5％）时MCM对苯和乙苯的模拟结果与实验结果较接近，如在苯一NO，反应体系中，MCM模拟的03峰值比实验值偏大20％；在湿度为5％～70％时，MCM模拟的乙苯光氧化0，峰值与实验值偏高约（10％～25％）．用MCM模拟了太阳光照条件下苯和乙苯的臭氧生成等值线，得到在它们浓度为（10～50）×10-9，NOx在（10～100）×10。时，苯和乙苯的6h臭氧贡献值分别为（3．1～33）×10-9和（2．6～122）×10-9，臭氧峰值范围分别是（3．5～54）×1019和（3．8～164）×10-9．此外，模拟得到苯和乙苯的最大增量反应活性（maximumincrementalreactivity，MIR）值分别为0．25／C和0．97／C（每单位碳）．该结果与Carter通过SAPRC机制得到的MIR值趋势一致．模拟得到苯和乙苯的最大臭氧反应活性（maximumozonereactivity，MOR）分别为0．73／C和1．03／C．苯的MOR值远高于Carter使用SAPRC得到的结果，说明根据Carter得到的苯MOR会低估苯的03潜势．

Ozone episodes during and after the 2018 Chinese National Day holidays in Guangzhou:Implications for the control of precursor VOCs

The impact of reducing industrial emissions of volatile organic compounds(VOCs)on ozone(O_(3))pollution is of wide concern particularly in highly industrialized megacities.In this study,O_(3),nitrogen oxides(NOx)and VOCs were measured at an urban site in the Pearl River Delta region during the 2018 Chinese National Day Holidays and two after-holiday periods(one with ozone pollution and another without).O_(3)pollution occurred throughout the 7-day holidays even industrial emissions of VOCswere passively reduced due to temporary factory shutdowns,and the toluene to benzene ratios dropped from∼10 during non-holidays to∼5 during the holidays.Box model(AtChem2-MCM)simulations with the input of observation data revealed that O_(3)formation was all VOC-limited,and alkenes had the highest relative incremental reactivity(RIR)during the holiday and non-holiday O_(3)episodes while aromatics had the highest RIR during the non-pollution period.Box model also demonstrated that even aromatics decreased proportionally to levels with near-zero contributions of industrial aromatic solvents,O_(3)concentrations would only decrease by less than 20%during the holiday and non-holiday O_(3)episodes and ozone pollution in the periods could not be eliminated.The results imply that controlling emissions of industrial aromatic solvents might be not enough to eliminate O_(3)pollution in the region,and more attention should be paid to anthropogenic reactive alkenes.Isoprene and formaldehyde were among the top 3 species by RIRs in all the three pollution and non-pollution periods,suggesting substantial contribution to O_(3)formation from biogenic VOCs.

Sources of ambient non-methane hydrocarbon compounds and their impacts on O_(3) formation during autumn,Beijing

The field observation of 54 non-methane hydrocarbon compounds(NMHCs)was conducted from September 1 to October 20 in 2020 during autumn in Haidian District,Beijing.The mean concentration of total NMHCs was 29.81±11.39 ppbv during this period,and alkanes were the major components.There were typical festival effects of NMHCs with lower concentration during the National Day.Alkenes and aromatics were the dominant groups in ozone formation potential(OFP)and OH radical loss rate(L_(OH)).The positive matrix factorization(PMF)running results revealed that vehicular exhaust became the biggest source in urban areas,followed by liquefied petroleum gas(LPG)usage,solvent usage,and fuel evaporation.The box model coupled with master chemical mechanism(MCM)was applied to study the impacts of different NMHCs sources on ozone(O_(3))formation in an O_(3)episode.The simulation results indicated that reducing NMHCs concentration could effectively suppress O_(3)formation.Moreover,reducing traffic-related emissions of NMHCs was an effective way to control O_(3)pollution at an urban site in Beijing.

山东临沂大气夏季典型时段臭氧污染特征及其控制因素分析

2020年6月,在山东省临沂城区开展臭氧(O_(3))及其前体物观测实验,基于观测数据结合MCM光化学模式模拟,对6月中旬O_(3)污染特例生成机理及控制机制进行了分析.结果发现,尽管观测期间降水较多,一旦天气转晴,O_(3)迅速积累并超标,1-h和8-hφ(O_(3))超标天数分别为10 d(频率32%)和14 d(45%).O_(3)日变化呈单峰模态,峰值出现在午后16:00.MCM模拟结果表明,光化学污染特例日O_(3)日均净生成反应速率为20×10^(-9)h^(-1),HO_(2)·+NO和RO_(2)·(除CH_(3)O_(2)·外)+NO反应分别贡献O_(3)生成的49.0%~51.1%和37.3%~40.2%;·OH+NO_(2)反应对O_(3)总消耗的贡献约为35.1%~57.4%.VOCs反应活性、增量反应活性RIR和基于EKMA曲线方法结果均表明O_(3)的生成对烯烃(主要优势单体为反-2-戊烯和反-2-丁烯),芳香烃(主要优势单体为对/间-二甲苯和甲苯)更为敏感,而对NO_(x)呈负敏感,即降低φ(VOCs)可使φ(O_(3))显著下降,而降低φ(NO_(x))反而会引起φ(O_(3))的上升.PMF源解析结果表明,溶剂使用挥发源和机动车尾气排放源对以上优势单体VOCs贡献显著.考虑机动车尾气排放NO对O_(3)的滴定效应,控制溶剂使用挥发源可以实现O_(3)污染精准有效控制.