HONO, Particulate Nitrite, and Snow Nitrite at a Midlatitude Urban Site during Wintertime

Abstract

Nitrous acid (HONO) plays an important role in the oxidative capacity of the atmosphere during wintertime via photolysis to produce hydroxyl radicals (OH). While it is known that HONO is emitted from the Arctic snowpack, sparse observations of HONO in the midlatitude urban wintertime environment have hindered our understanding of cold-season atmospheric chemistry. In this study, measurements of ambient HONO, particulate nitrite (pN­(III); N­(III) = NO2(aq) – + HONO(aq) + H2ONO(aq) +), and snow nitrite (sN­(III)) were conducted in Kalamazoo, Michigan during January–February 2018. Elevated levels of HONO and particulate nitrite were observed over snow-covered ground, likely due to emissions of HONO from the snowpack, as well as weak turbulent mixing in the atmospheric boundary layer. The noontime peak in HONO of 87 ± 60 (1σ) parts per trillion (ppt) over snow-covered ground suggests photochemical snowpack HONO production, likely in part through snowpack nitrate photolysis, with only a minor contribution from particulate nitrate photolysis. High concentrations of snow nitrite (0.4 ± 0.3 (1σ) μM) support the hypothesis that the snowpack is a significant source of HONO to the atmosphere. On average, the OH production rate from HONO photolysis, in the near-surface atmosphere (≈ 2 m above ground), was calculated to be about an order of magnitude higher than that from O3 photolysis over snow-covered ground. Future studies are needed to quantify HONO emissions from the midlatitude urban snowpack, given expected HONO production due to high concentrations of snow nitrate and nitrite from anthropogenic particulate nitrate and nitrite deposition.

Global inorganic nitrate production mechanisms: comparison of a global model with nitrate isotope observations

“…Thus, NO both emitted and oxidized to NO 2 at night will lead to A night = 0.5 (half of the O atoms of NO 2 originate from O 3 ). Although isotopic exchange between NO + NO 2 (Sharma et al, 1970) and NO 2 and NO 3 via thermal dissociation of N 2 O 5 (Connell and Johnston, 1979) will tend to increase 17 O(NO) above its emitted value of 0 ‰, the bulk 17 O value of the NO x plus NO 3 system will be lower at night than during the daytime due to the absence of photochemical cycling at night (Michalski et al, 2014;Morin et al, 2011). Since the atmospheric lifetime of NO x near the surface against nighttime oxidation to nitrate (R2 + R4 + R5) is typically greater than 24 h (Fig.…”

Improving the representation of HONO chemistry in CMAQ and examining its impact on haze over China

“…Such pathways are not the focus this study and are not included in the current model. A recent study (Chen et al, 2019) suggests that HONO also can form on snow-covered ground, which can potentially affect wintertime air quality. Thus, a future study incorporating such chemical reactions to comprehensively examine the impact of HONO chemistry on air quality in different seasons and geographical areas is envisioned.…”

Coupled Air Quality and Boundary-Layer Meteorology in Western U.S. Basins during Winter: Design and Rationale for a Comprehensive Study

“…Surface snowpacks also directly impact atmospheric composition by serving as a sink/reservoir for atmospheric trace gases and particles upon deposition and as a source from reactions on and within the snow grain surface (Grannas et al 2007). For example, nitrate deposited on the snowpack undergoes photolysis to produce NOx and HONO released to the air above (Chen et al 2019;Honrath et al 2000;Michoud et al 2015;Zatko et al 2016). Snowpack photochemistry also contributes to near-surface OH through the production and subsequent photolysis of H2O2 and carbonyls, including formaldehyde, acetaldehyde, and acetone (Couch et al 2000).…”

“…A second important wintertime heterogeneous and multiphase reaction is the production of nitrous acid (HONO), a radical reservoir whose photolysis may be a large OH source that affects urban air quality (e.g., Fu et al 2019). Numerous heterogeneous and multiphase HONO sources have been proposed, such as photochemical generation from snowpacks (Chen et al 2019) and photolysis of nitrate aerosol (Ye et al 2017), although the latter remains controversial (Romer et al 2018). Given the variety of potential HONO sources and associated uncertainties,…”