Measurement of free radicals OH and HO2 in Los Angeles smog
Measurement of free radicals OH and HO2 in Los Angeles smog
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DOI：
10.1029/1998jd100113
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发表时间：
1999-05-20
影响因子：
4.4
通讯作者：
O'Brien, RJ
中科院分区：
文献类型：
--
作者：
George, LA;Hard, TM;O'Brien, RJ
大气自由基羟基和过氧化氢（OH和HO 2，统称HOx）是造成二次或光化学空气污染的催化剂。氧化剂和酸形成的化学机理是昂贵的空气污染控制策略的基础，必须准确地预测这些自由基的浓度。我们已经使用了气体膨胀荧光分析（FAGE）技术进行的第一次同时，在现场测量这两个自由基在高度污染的空气中的洛杉矶自由基实验。还进行了一整套辅助测量，包括各种碳氢化合物、一氧化碳、醛、一氧化氮、二氧化氮和臭氧沿着气象参数。使用这套测量，我们测试了集总化学机制准确预测污染空气中自由基浓度的能力。模型预测与测量的自由基浓度的比较显示，一般良好的协议OH早，晚在一天中，包括傍晚时分，当OH持续在低浓度天黑后。然而，在中午期间，模型[OH]高约50%。在清晨，HO 2的一致性相当好，但中午模型计算的HO 2浓度明显过高。当我们使用我们测量的HO 2浓度作为模型输入时，计算和测量的OH浓度之间的一致性得到改善。看来可能是（1）模型的HOx源太大，（2）在洛杉矶空气中存在未考虑的HOx损失过程，和/或（3）反应机制中RO 2/HO 2自由基化学的复杂参数化不能充分描述这些自由基在洛杉矶大气中的行为。
Atmospheric free radicals hydroxyl and hydroperoxyl (OH and HO2, collectively HOx) are the catalysts that cause secondary or photochemical air pollution. Chemical mechanisms for oxidant and acid formation, on which expensive air pollution control strategies are based, must accurately predict these radical concentrations. We have used the fluorescence assay with gas expansion (FAGE) technique to carry out the first simultaneous, in situ measurements of these two radicals in highly polluted air during the Los Angeles Free Radical Experiment. A complete suite of ancillary measurements was also made, including speciated hydrocarbons, carbon monoxide, aldehydes, nitric oxide, nitrogen dioxide, and ozone along with meteorological parameters. Using this suite of measurements, we tested the ability of a lumped chemical mechanism to accurately predict radical concentrations in polluted air. Comparison of model predictions with measured radical concentrations revealed generally good agreement for OH early and late in the day, including the early evening hours, when OH persisted at low concentrations after dark. During midday, however, modeled [OH] was high by about 50%. Agreement for HO2 was quite good in the early morning hours, but model-calculated HO2 concentrations were significantly too high during midday. When we used our measured HO2 concentrations as model input, agreement between calculated and measured OH concentrations was improved. It seems likely that(1) the model's HOx sources are too large, (2) there are unaccounted HOx loss processes in Los Angeles air, and/or (3) the complex parameterization of RO2/HO2 radical chemistry in the reaction mechanism does not adequately describe the behavior of these radicals in the Los Angeles atmosphere.