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Title: Potential sources of nitrous acid (HONO) and their impacts on ozone : a WRF-Chem study in a polluted subtropical region
Authors: Zhang, L
Wang, T 
Zhang, Q
Zheng, J
Xu, Z
Lv, M
Keywords: Heterogeneous conversion
Nitrous acid
Soil bacteria
Issue Date: 2016
Publisher: Wiley-Blackwell
Source: Journal of geophysical research. Atmospheres, 2016, v. 121, no. 7, p. 3645-3662 How to cite?
Journal: Journal of geophysical research. Atmospheres 
Abstract: Current chemical transport models commonly undersimulate the atmospheric concentration of nitrous acid (HONO), which plays an important role in atmospheric chemistry, due to the lack or inappropriate representations of some sources in the models. In the present study, we parameterized up-to-date HONO sources into a state-of-the-art three-dimensional chemical transport model (Weather Research and Forecasting model coupled with Chemistry: WRF-Chem). These sources included (1) heterogeneous reactions on ground surfaces with the photoenhanced effect on HONO production, (2) photoenhanced reactions on aerosol surfaces, (3) direct vehicle and vessel emissions, (4) potential conversion of NO2 at the ocean surface, and (5) emissions from soil bacteria. The revised WRF-Chem was applied to explore the sources of the high HONO concentrations (0.45-2.71 ppb) observed at a suburban site located within complex land types (with artificial land covers, ocean, and forests) in Hong Kong. With the addition of these sources, the revised model substantially reproduced the observed HONO levels. The heterogeneous conversions of NO2 on ground surfaces dominated HONO sources contributing about 42% to the observed HONO mixing ratios, with emissions from soil bacterial contributing around 29%, followed by the oceanic source (∼9%), photochemical formation via NO and OH (∼6%), conversion on aerosol surfaces (∼3%), and traffic emissions (∼2%). The results suggest that HONO sources in suburban areas could be more complex and diverse than those in urban or rural areas and that the bacterial and/or ocean processes need to be considered in HONO production in forested and/or coastal areas. Sensitivity tests showed that the simulated HONO was sensitive to the uptake coefficient of NO2 on the surfaces. Incorporation of the aforementioned HONO sources significantly improved the simulations of ozone, resulting in increases of ground-level ozone concentrations by 6-12% over urban areas in Hong Kong and the Pearl River Delta region. This result highlights the importance of accurately representing HONO sources in simulations of secondary pollutants over polluted regions.
ISSN: 2169-897X
EISSN: 2169-8996
DOI: 10.1002/2015JD024468
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