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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Production of peroxy radicals at night via reactions of ozone and the nitrate radical in the marine boundary layer
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Production of peroxy radicals at night via reactions of ozone and the nitrate radical in the marine boundary layer

机译：晚上通过海洋边界层中的臭氧与硝酸根反应生成过氧自由基

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In this paper, a substantial set of simultaneous measurements of the sum of peroxy radicals, [HO2+RO2], NO3, hydrocarbons (HCs), and ozone, taken at Mace Head on the Atlantic coast of Ireland in spring 1997, is presented. Conditions encountered during the experiment ranged from semipolluted air masses advected from Britain and continental Europe to clean air masses off the North and mid-Atlantic, where mixing ratios of pollution tracers approached Northern Hemispheric background mixing ratios. Average mixing ratios of peroxy radicals varied from 2.5 to 5.5 parts per trillion by volume (pptv) at night depending on wind sector, and were observed to decay only very slowly from late afternoon to early morning (0.1-0.5 pptv h(-1)). Measurements of OH and HO2 on two nights using the Fluorescence Assay by Gas Expansion (FAGE) technique give an upper limit for [OH] of 2.5x10(5) molecules cm(-3) and an average upper limit [HO2]/[HO2+RO2] ratio of 0.27. A modeling study of the (1)/e lifetimes of the peroxy radicals, assuming no radical production at night, yielded mean lifetimes of between similar to 8-23 min for HO2 and 3-18 min for CH3O2. Given these lifetimes, it may be concluded that the peroxy-radical mixing ratios observed could not be maintained without substantial production at night. No significant correlation is observed between measured [HO2+RO2] and [NO3] under any conditions. Calculation of the reaction rates for ozone and NO, with hydrocarbons (HCs) shows that the ozone-initiated oxidation routes of HCs outweighed those of NO3 in the NE, SE and NW wind sectors. In the SW sector, however, the two mechanisms operated at similar rates on average, and oxidation by NO3 was the dominant route in the westerly sector. The oxidation of alkenes at night by ozone was greater by a factor of 4 than that by NO3 over the whole data set. The HC degradation rates from the three "westerly" sectors, where tracer mixing ratios were relatively low, may be representative of the nighttime oxidative capacity of the marine boundary layer throughout the background Northern Hemisphere. Further calculations using literature values for OH yields and inferred RO2 yields from the ozone-alkene reactions show that peroxy radicals derived from the ozone reactions were likely to make up the major part of the peroxy-radical signal at night (mean value 66%). However, the NO3 source was of similar magnitude in the middle of the night, when [NO3] was generally at its maximum. The estimated total rates of formation of peroxy radicals are much higher under semipolluted conditions (mean 8.0x10(4) molecules cm(-3) s(-1) in the SE wind sector) than under cleaner conditions (mean 2.4x10(4) molecules cm(-3) s(-1) in the westerly wind sector). A model study using a campaign-tailored box model (CTBM) for semipolluted conditions shows that the major primary sources of OH, HO2, and CH3O2 (the most abundant organic peroxy radical) were the Criegee biradical intermediates formed in the reactions of ozone with alkenes. [References: 62]
机译：本文介绍了一组大量的同时测量过氧自由基，[HO2 + RO2]，NO3，碳氢化合物（HCs）和臭氧的方法，该方法于1997年春季在爱尔兰大西洋沿岸的梅斯角进行了测量。实验期间遇到的条件范围从英国和欧洲大陆吹出的半污染气团到北大西洋和中大西洋以外的干净气团，其中污染示踪剂的混合比接近北半球本底混合比。取决于风能部门，过氧自由基的平均混合比在夜间从2.5到5.5万亿分之体积（pptv）变化，并且观察到从午后到清晨（0.1-0.5 pptv h（-1））衰减非常缓慢）。使用气体膨胀荧光分析（FAGE）技术在两个晚上测量OH和HO2，得出[OH]的上限为2.5x10（5）分子cm（-3），平均上限为[HO2] / [HO2] + RO2]比为0.27。对过氧自由基的（1）/ e寿命进行的建模研究（假设晚上没有自由基产生）得出的平均寿命介于HO2的8-23分钟和CH3O2的3-18分钟之间。给定这些寿命，可以得出结论，如果没有大量夜间生产，就无法维持观察到的过氧自由基混合比。在任何条件下，测得的[HO2 + RO2]和[NO3]之间均未发现明显的相关性。计算臭氧与NO与碳氢化合物（HCs）的反应速率表明，在东北，东南和西北风区，HCs的臭氧引发的氧化途径超过了NO3。然而，在西南部门，这两种机制的平均运行速度相似，而NO3氧化是西风部门的主要途径。在整个数据集中，夜间臭氧对烯烃的氧化作用比NO3对烯烃的氧化作用高4倍。示踪剂混合比相对较低的三个“西风”区的HC降解率可能代表整个北半球背景海洋边界层的夜间氧化能力。使用文献中有关臭氧-烯烃反应的OH收率和推断的RO2收率的值进行的进一步计算表明，臭氧反应中产生的过氧自由基很可能构成夜间过氧自由基信号的主要部分（平均值为66％）。但是，当[NO3]通常达到最大值时，在午夜时NO3源的大小相似。在半污染条件下（东南风领域中平均8.0x10（4）分子cm（-3）s（-1）分子），过氧自由基的估计总形成速率要比在清洁条件下（平均2.4x10（4））高得多西风扇区中的分子cm（-3）s（-1））。使用运动量身定制的盒子模型（CTBM）进行半污染条件的模型研究表明，OH，HO2和CH3O2（最丰富的有机过氧自由基）的主要主要来源是臭氧与烯烃反应中形成的Criegee双自由基中间体。 [参考：62]

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