HONO Budget and Its Role in Nitrate Formation in the Rural North China Plain

Abstract

Nitrous acid (HONO) is a major precursor of tropospheric hydroxyl radical (OH) that accelerates the formation of secondary pollutants. The HONO sources, however, are not well understood, especially in polluted areas. Based on a comprehensive winter field campaign conducted at a rural site of the North China Plain, a box model (MCM v3.3.1) was used to simulate the daytime HONO budget and nitrate formation. We found that HONO photolysis acted as the dominant source for primary OH with a contribution of more than 92%. The observed daytime HONO could be well explained by the known sources in the model. The heterogeneous conversion of NO2 on ground surfaces and the homogeneous reaction of NO with OH were the dominant HONO sources with contributions of more than 36% and 34% to daytime HONO, respectively. The contribution from the photolysis of particle nitrate and the reactions of NO2 on aerosol surfaces were found to be negligible in clean periods (2%) and slightly higher during polluted periods (8%). The relatively high OH levels due to fast HONO photolysis at the rural site remarkably accelerated gas-phase reactions, resulting in the fast formation of nitrate as well as other secondary pollutants in the daytime.

Measurement report: Fast photochemical production of peroxyacetyl nitrate (PAN) over the rural North China Plain during cold-season haze events

“…It proves the similar source of PAN and HCHO, also demonstrates a potential impact of HCHO photolysis on PAN increase at this rural site with accelerated photochemistry. The sources of HOx radical during cold days have been a subject of recent interest in the field of atmospheric chemistry over the NCP region (Tan et al, 2018;Xue et al, 2020), and most of them reported the importance of HONO in OH radical and atmospheric oxidation capacity during cold days over the NCP. By comparisons, our results at the SDZ site presents a much lower HONO concentration (average: Tan et al (2018) and Xue et al (2020).…”

“…The sources of HOx radical during cold days have been a subject of recent interest in the field of atmospheric chemistry over the NCP region (Tan et al, 2018;Xue et al, 2020), and most of them reported the importance of HONO in OH radical and atmospheric oxidation capacity during cold days over the NCP. By comparisons, our results at the SDZ site presents a much lower HONO concentration (average: Tan et al (2018) and Xue et al (2020). As the SDZ site is located in the north border of the NCP region, which is much cleaner than the suburban and rural site in Tan et al (2018) and Xue et al (2020), then less affected by shortlive species, such as NOx and HONO.…”

“…Thus, photochemical production of PAN could be determined by the oxidation of volatile organic compounds (VOCs) with hydroxyl radical (OH) in the presence of nitrogen oxide (NOx = NO + NO2). Nitrous acid (HONO) is usually considered as the dominant source of OH radical in the early morning (Alicke et al, 2003) and during cold days (Hendrick et al, 2014;Kim et al, 2014;Lu et al, 2019) that is mainly generated from direct traffic emissions and heterogeneous conversion of NO2 on ground and aerosol surfaces (Xue et al, 2020;Liu et al, 2021). In addition, photolysis of carbonyls may also greatly influence HOx (HOx = OH + HO2) and ozone (O3) production at lower NOx concentrations during cold seasons (Edwards et al, 2014;Li et al, 2021).…”

Development of a Laser-Photofragmentation Laser-Induced Fluorescence instrument for the detection of nitrous acid and hydroxyl radicals in the atmosphere

“…As a result, HONO photolysis can dominate OH production during the morning hours in some environments (Volkamer et al, 2010), but decrease in importance during the day as the concentration of HONO decreases. 40 However, in several instances HONO photolysis has been shown to be a significant OH source through the day (Kleffmann et al, 2005;Acker et al, 2006;Ren et al, 2013;Griffith et al, 2016;Xue et al, 2020). This is mainly due to higher-than-expected daytime HONO mixing ratios that cannot be attributed to gas-phase reactions (R1-R3) (Tang et al, 2015;Lee et al, 2016;Meusel et al, 2016;Xue et al, 2020).…”

“…Other HONO sources include direct emission from vehicles or other combustion sources (Kirchstetter et al, 1996;Kurtenbach 45 et al, 2001;Li et al, 2008;Xu et al, 2015), direct photolysis of some species (Bejan et al, 2006;Zhou et al, 2011), photo-enhanced surface reactions (George et al, 2005;Stemmler et al, 2006), and release from soil due to biological processes (Su et al, 2011;Oswald et al, 2013;Weber et al, 2015;Meusel et al, 2018). Lastly, several production pathways involving the heterogeneous conversion of NO2 to HONO on soil, leaf canopies, aerosols, and other surfaces have been suggested to explain higher-than-expected HONO mixing ratios observed during some field campaigns (Kleffmann et al, 1998;Ramazan et al, 2004;Stutz et al, 2004;Xue et al, 2020). 50 HONO is also an important pollutant within the indoor environment.…”