Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign - Part 2: Model comparison and radical budget
Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign - Part 2: Model comparison and radical budget
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DOI：
10.5194/acp-9-6655-2009
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发表时间：
2009-01-01
影响因子：
6.3
通讯作者：
Holder, H.
中科院分区：
文献类型：
--
作者：
Dusanter, S.;Vimal, D.;Holder, H.
2006年3月，作为MILAGRO（大城市倡议：地方和全球研究观测）项目的一部分，在墨西哥城都市区（MCMA）实地活动期间对羟基（OH）和过氧氢（HO 2）自由基进行了测量。这些测量提供了一个独特的机会来测试目前的大气ROx（OH + HO 2 + RO 2）光化学模型在污染条件下。基于区域大气化学机制（RACM）的零维箱模式的约束条件为10分钟平均的24个J值和97种化学物质的浓度。本研究强调了与污染条件下ROx化学相关的几个问题：（i）在中等活动基础上，早上测量的OH和HO 2浓度低于预测值，这表明在污染条件下，当前的大气模型中缺少一个重要的自由基来源，与以前的城市实地活动一致。(ii)模型预测的HO 2/OH比低估了测量NO混合比高于5 ppb，也与以前的城市实地活动。这表明在高NOx条件下，HO 2到OH的传播速率可能被模型高估，或者将OH转化为HO 2的过程可能从化学机理中缺失。每天早上8点40分（m.-下午6时40分），自由基收支分析表明，HONO光解、HCHO光解、O-3-烯烃反应和二羰基化合物光解是主要的自由基来源。O-3的光解作用占总自由基产生量的不到6%。
Measurements of hydroxyl ( OH) and hydroperoxy (HO2) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) project during March 2006. These measurements provide a unique opportunity to test current models of atmospheric ROx (OH + HO2 + RO2) photochemistry under polluted conditions. A zero-dimensional box model based on the Regional Atmospheric Chemical Mechanism (RACM) was constrained by 10-min averages of 24 J-values and the concentrations of 97 chemical species. Several issues related to the ROx chemistry under polluted conditions are highlighted in this study: (i) Measured concentrations of both OH and HO2 were underpredicted during morning hours on a median campaign basis, suggesting a significant source of radicals is missing from current atmospheric models under polluted conditions, consistent with previous urban field campaigns. (ii) The model-predicted HO2/OH ratios underestimate the measurements for NO mixing ratios higher than 5 ppb, also consistent with previous urban field campaigns. This suggests that under high NOx conditions, the HO2 to OH propagation rate may be overestimated by the model or a process converting OH into HO2 may be missing from the chemical mechanism. On a daily basis ( 08: 40 a. m.-06: 40 p. m.), an analysis of the radical budget indicates that HONO photolysis, HCHO photolysis, O-3-alkene reactions and dicarbonyls photolysis are the main radical sources. O-3 photolysis contributes to less than 6% of the total radical production.