title: Review of heterogeneous photochemical reactions of NOy on aerosol - A possible daytime source of nitrous acid (HONO) in the atmosphere.
abstract: As an important precursor of hydroxyl radical, nitrous acid (HONO) plays a key role in the chemistry of the lower atmosphere. Recent atmospheric measurements and model calculations show strong enhancement for HONO formation during daytime, while they are inconsistent with the known sources in the atmosphere, suggesting that current models are lacking important sources for HONO. In this article, heterogeneous photochemical reactions of nitric acid/nitrate anion and nitrogen oxide on various aerosols were reviewed and their potential contribution to HONO formation was also discussed. It is demonstrated that HONO can be formed by photochemical reaction on surfaces with deposited HNO3, by photocatalytic reaction of NO2 on TiO2 or TiO2-containing materials, and by photochemical reaction of NO2 on soot, humic acids or other photosensitized organic surfaces. Although significant uncertainties still exist in the exact mechanisms and the yield of HONO, these additional sources might explain daytime observations in the atmosphere.
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. jzma@rcees.ac.cn
authors.forename: Jinzhu
authors.initials: J
authors.lastname: Ma
authors.forename: Yongchun
authors.initials: Y
authors.lastname: Liu
authors.forename: Chong
authors.initials: C
authors.lastname: Han
authors.forename: Qingxin
authors.initials: Q
authors.lastname: Ma
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.forename: Hong
authors.initials: H
authors.lastname: He
mesh_terms: D000336:Aerosols / Q000138:chemical synthesis*; D001272:Atmosphere / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D009608:Nitrous Acid / Q000737:chemistry*; D010777:Photochemistry
chemical_list: D000336:Aerosols; D017665:Hydroxyl Radical; D009608:Nitrous Acid