Impacts of atmospheric degradation mechanisms of biogenic volatile organic compounds on aerosol formation potential and property of cloud condensation nuclei

利用内容为6m~3的光化学反应室研究了挥发性有机化合物(VOCs)生成二次有机气溶胶(SOA)的过程。异戊二烯是最丰富的生物成因碳氢化合物，其在大气中的主要汇是白天与OH自由基的反应。由于异戊二烯的排放速率较大，了解异戊二烯氧化是否会导致异戊二烯的生成，以及控制异戊二烯生成量的主导因素是什么是很重要的。在异戊二烯的NOx光氧化反应中，在光化学臭氧形成后总是观察到SOA的生成。随着初始NOx浓度的降低，异戊二烯在SOA形成前的损失浓度降低，而气溶胶总产率随NOx浓度的增加而增加。实验结果可以用RO_2-自由基与HO_2自由基的反应促进可凝聚物种的形成来解释。异戊二烯臭氧化反应中也观察到了SO_2的生成。气溶胶形成产额为Wa…添加过量的OH-自由基清除剂对S的抑制作用更明显，而气溶胶形成抑制的大小对清除剂的种类不敏感。在有OH-自由基清除剂CO存在的情况下观察到的气溶胶质谱与在没有清除剂的情况下观察到的气溶胶质量谱不同。这些结果表明，OH引发的反应是产生SOA的关键，而与异戊二烯的直接臭氧反应产生的SOA比OH-氧化反应产生的SOA少。还测量了甲苯、对乙基甲苯、对二甲苯和1，3，5-三甲苯等芳香烃(AHC)的光氧化反应的SOA产率：每个AHC的SOA产率取决于ARC的初始浓度。为了解释目前的实验结果，对以前提出的一种反应方案进行了检验，在该方案中，假定可凝聚产物是由初级氧化产物与臭氧的二次反应形成的。对于每个AHC，先前提出的两步反应方案成功地解释了在不同条件下所测得的SOA浓度与反应AHC浓度的函数关系。较少

Secondary organic aerosol (SOA) formation from volatile organic compounds (VOCs) was investigated using a photochemical reaction chamber with an inner volume of 6-m^3. Isoprene is the most abundant biogenic hydrocarbon and its dominant sink in the atmosphere is the reaction with OH radicals in the daytime. Due to its large emission rate, it is important to know if isoprene oxidation leads to SOA production and what is a dominant factor to control the SOA formation yield. SOA formation in the NO_x-photooxidation of isoprene was always observed after photochemical ozone was formed. The concentration of isoprene lost before SOA was formed became lower with decreasing the initial Nox concentration, whereas the total aerosol yield increased with increasing NOT. Experimental results could be explained in terms that RO_2-radical reactions with HO_2 radical contribute the formation of condensable species.SOA formation in the isoprene ozonolysis was also observed. The aerosol formation yield wa … More s markedly depressed by adding excess amount of OH-radical scavengers, while the size of depression of aerosol formation was insensitive to the species of scavenger. Aerosol mass spectrum observed in the presence of OH-radical scavenger, CO, was different from that observed in the absence of the scavenger. These results suggest that OH-initiated reactions are essential to the production of SOAandthe direct ozone reaction with isoprene less produces SOA than OH-oxidation reaction.The SOA mass yields from the photooxidation of aromatic hydrocarbons (AHCs), such as toluene, p-ethyltoluene, p-xylene and 1, 3, 5-trimethylbenzene, were also measured: The SOA yield from each AHC depended on the initial ARC concentration. A previously proposed reaction scheme, in which condensable products are assumed to be formed by secondary reactions of primary oxidation products with ozone, was examined for the interpretations of the present experimental results. As for each AHC, the SOA concentrations measured as a function of the concentration of reacted AHC were successfully explained under various conditions by the previously proposed two-step reaction scheme. Less