Kleffmann Jörg
Physikalische Chemie/FB C, Bergische Universität Wuppertal, Gaussstrasse 20, 42119 Wuppertal, Germany.
Chemphyschem. 2007 Jun 4;8(8):1137-44. doi: 10.1002/cphc.200700016.
Nitrous acid (HONO) is an important precursor of the hydroxyl radical (OH), the self-cleaning agent of the atmosphere and a key species in the formation of harmful photooxidants during summer smog. Recent field measurements using very sensitive HONO instruments have shown that daytime HONO concentrations are much higher than has been assumed previously and that the contribution of HONO to the radical formation was underestimated in the past. A strong photochemical HONO source has been proposed, which contributes to the primary OH radical production up to 56 %. These exciting results initiated new laboratory studies, in which new sources of HONO have been identified. It is demonstrated that HONO is photochemically formed 1) on surfaces treated with nitric acid, 2) by reduction of NO(2) on photosensitized organic surfaces like humic acids and c) in the gas phase photolysis of ortho-substituted nitroaromatics. Although significant uncertainties still exist on the exact mechanisms, these additional sources might explain daytime observations in the atmosphere and demonstrate that HONO should be generally measured in field campaigns, besides other radical sources.
亚硝酸（HONO）是羟基自由基（OH）的重要前体，羟基自由基是大气的自净剂，也是夏季烟雾中有害光氧化剂形成过程中的关键物质。最近使用非常灵敏的HONO仪器进行的实地测量表明，白天HONO的浓度比之前假设的要高得多，而且过去HONO对自由基形成的贡献被低估了。有人提出了一个强大的光化学HONO源，它对初级OH自由基生成的贡献高达56%。这些令人兴奋的结果引发了新的实验室研究，在这些研究中发现了HONO的新来源。结果表明，HONO可通过光化学方式在以下情况形成：1）在硝酸处理过的表面上；2）在腐殖酸等光敏有机表面上通过NO(2)的还原作用形成；以及3）在邻位取代硝基芳烃的气相光解过程中形成。尽管在确切机制方面仍存在重大不确定性，但这些额外的来源可能解释大气中的白天观测结果，并表明除了其他自由基源之外，在野外测量中通常还应测量HONO。
