Gaseous nitrous acid (HONO) plays an important role in the oxidation capacity of the troposphere. In the marine boundary layer, there exist an active daytime HONO source that sustains the observed HONO mixing ratio against its fast photochemical loss. The photolysis of particulate nitrate (pNO3), which proceeds at a much faster rate than gaseous nitric acid, could be a significant source of HONO. 

We conducted extensive field measurements to determine the temporal distribution HONO along with several reactive nitrogen species in the marine atmosphere at Tudor Hill Marine Atmospheric Observatory in Bermuda (Zhu et al., 2022, ACP). Laboratory experiments were conducted to investigate the importance of pNO3 as a photolytic HONO source. 

Low-molecular-weight (LMW) carbonyl compounds, including acetaldehyde, glyoxal and methylglyoxal, are important intermediate species that affect atmospheric oxidation capacity and marine aerosol formation. Earlier studies indicated that the ocean might be an important source of these carbonyls to the troposphere. However, the direction and magnitude of their air-sea exchange remained highly uncertain due to paucity of their in situ concentration data. 

This study (Zhu & Kieber, 2019, ES&T), conducted in the Northwest Atlantic Ocean, provided new data regarding carbonyl concentrations in oceanic waters. Evidences showed that air-sea flux of LMW carbonyls only serves as a minor contributing factor for the cycling of these compounds in the marine environment. In fact, biogeochemical factors that control carbonyl concentrations in surface oceanic waters remain poorly understood. Our findings suggested that known biogeochemical production and loss rates (e.g., photochemical and air-sea flux) failed to explain the observed concentrations of LMW carbonyls in surface oceanic waters.