Photoreduction of Nitrate to HONO and NOx by Organic Matter in the Presence of Iron and Aluminum

IF 2.9 3区 化学 Q2 CHEMISTRY, MULTIDISCIPLINARY
Elizabeth Melssen, David L. Bish, Yaroslav Losovyj and Jonathan D. Raff*, 
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Abstract

Nitrogen oxides (NOy) such as NO, NO2, and HONO control the oxidative capacity of the lower atmosphere. Studies have shown that photolysis of nitrate on atmospheric surfaces is an efficient source of nitrogen oxides through a process termed "renoxification;" however, the mechanisms responsible for this process remain poorly understood, leading to difficulties in modeling atmospheric composition. This work aims to elucidate the mechanism of NOy formation from nitrate photolysis on model boundary layer surfaces comprised of mixtures of organic matter (citrate and Suwanee River fulvic acid) and environmentally relevant metals (e.g., Al3+ and Fe3+). Results show that in the presence of organic matter, photochemical yields of NOy were enhanced by a factor of between 5 and 15 compared with photolysis of pure nitrate controls. Known nitrate photochemistry mechanisms are unable to explain this enhancement, suggesting that a fraction of nitrate is directly converted to NOy by strong reductants produced photochemically from organic matter. The addition of Fe (hydr)oxides catalyzed both the reduction of NO2 to HONO and further reduction of HONO to NO via Fe2+, which is formed through photoreduction of Fe-organic matter coordination complexes. In addition, this study assesses the contribution of surface acidity and visible light attenuation on the product yields. The results support a growing body of evidence that strong reductants generated photochemically via organic matter are an important and unrecognized pathway for renoxification on both soil and airborne surfaces (e.g., mineral dust and aerosols).

Abstract Image

铁和铝存在下有机物光还原硝酸盐生成HONO和NOx的研究
氮氧化物(NOy)如NO、NO2和HONO控制低层大气的氧化能力。研究表明,大气表面硝酸盐的光解作用是氮氧化物的有效来源,这一过程被称为“再氧化”;然而,对这一过程的机制仍然知之甚少,导致在模拟大气成分方面存在困难。本研究旨在阐明由有机物质(柠檬酸盐和苏瓦尼河黄腐酸)和环境相关金属(如Al3+和Fe3+)混合组成的模型边界层表面上硝酸盐光解生成NOy的机制。结果表明,在有有机质存在的情况下,NOy光化学产率比纯硝酸盐对照提高了5 ~ 15倍。已知的硝酸盐光化学机制无法解释这种增强,这表明部分硝酸盐通过有机物质光化学产生的强还原剂直接转化为NOy。Fe(水合)氧化物的加入既催化NO2还原为HONO,又通过Fe-有机物配位配合物光还原形成的Fe2+将HONO进一步还原为NO。此外,本研究还评估了表面酸度和可见光衰减对产品收率的贡献。这些结果支持了越来越多的证据,即通过有机物质光化学产生的强还原剂是土壤和空气表面(如矿物粉尘和气溶胶)再氧化的重要途径,但尚未被认识到。
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来源期刊
ACS Earth and Space Chemistry
ACS Earth and Space Chemistry Earth and Planetary Sciences-Geochemistry and Petrology
CiteScore
5.30
自引率
11.80%
发文量
249
期刊介绍: The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.
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