Nitrous Acid (HONO) Formation from the Irradiation of Aqueous Nitrate Solutions in the Presence of Marine Chromophoric Dissolved Organic Matter: Comparison to Other Organic Photosensitizers

Abstract

Nitrous acid (HONO), a highly reactive trace atmospheric gas, is often underestimated in global atmospheric models due to the poor understanding of its sources and sinks, especially in the marine boundary layer (MBL). Herein, we have investigated HONO formation from the irradiation of nitrate solutions in the presence of increasingly complex photosensitizers including marine dissolved organic matter (m-DOM), which contains chromophoric organic matter, collected from a large-scale mesocosm experiment. In particular, aqueous nitrate solutions in the presence of m-DOM, humic acid (HA), and 4-benzoylbenzoic acid (4-BBA) as well as ethylene glycol (EG) were irradiated with a solar simulator. Gas-phase HONO and NO 2 produced during the irradiation of these samples were detected using incoherent broad band cavity enhanced absorption spectroscopy (IBBCEAS). The relative amounts of HONO and NO 2 formation varied for the different samples. The addition of all of these different organic containing samples (m-DOM, HA, 4-BBA, and EG) to nitrate solutions caused an enhancement in HONO formation, with m-DOM showing the greatest total amount over a 6 h time period. Mechanisms for this enhancement are discussed as well as the strong pH dependence, with the greatest amount of HONO at a low pH. Overall, HONO formation from nitrate photolysis in the presence of m-DOM provides insights into the HONO formation pathway in the MBL and ultimately contributes to improving atmospheric models.

Nitrogen oxides in the free troposphere: Implications for tropospheric oxidants and the interpretation of satellite NO2 measurements

“…The fraction of NO3at the surface is larger in the presence of halides in sea salt aerosols (Wingen et al, 2008;Richards-Henderson et al, 2013;Zhang et al, 2020). Other factors that could contribute to higher EFs include high aerosol [H + ] (Scharko Mora Garcia et al, 2021) and the presence of organic species that can act as photosensitizers, H-donors, electron donors, or promote secondary reactions (Ye et al, 2019;Mora Garcia et al, 2021). Laboratory studies on NaNO3 and NH4NO3 particles find EFs of less than 10 (Shi et al, 2021), suggesting that aerosol composition is an important factor in the photolysis rate of pNO3 -.…”

Snowmelt Leads to Seasonal Nitrous Acid Formation Across Northwestern China

“…Both NO 2 and O 2 •− are precursors of HONO and/or NO 2 − reactions (8-11). Besides, another study suggested the aqueous electron reduces nitrate into nitrite reaction (14) (Mora Garcia et al, 2021).…”

Aqueous SOA formation from photosensitized guaiacol oxidation: Comparison between non-phenolic and phenolic methoxybenzaldehydes as photosensitizers in the absence and presence of ammonium nitrate

“…On a related note, the significance of photosensitization by BrC (via formation of solvated electrons; Wang et al, 2021) and marine dissolved organic matter (via O 2 •formation; Garcia et al, 2021) in enhanced nitrite production from nitrate photolysis have been reported. A recent study from our group has shown that glyoxal photo-oxidation mediated by both nitrate photolysis and photosensitization can significantly enhance the atmospheric sink of glyoxal (Zhang et al, 2022).…”