Atmospheric Nitrous Acid in Contrasting Environments in North China

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Photochemistry

Background:

• Nitrous acid (HONO) is a key precursor to hydroxyl radicals (OH), influencing tropospheric photochemistry and atmospheric oxidation.
• Quantitative understanding of HONO formation, particularly in marine environments, remains limited.

Purpose of the Study:

• To quantify HONO formation in diverse environments, including urban, mountain, and coastal sites.
• To identify and characterize HONO sources, with a focus on potential marine contributions.

Main Methods:

• Utilized an updated observation-based model to analyze HONO levels.
• Compared modeled HONO formation with observed data across four distinct geographical locations.

Main Results:

• Model accurately reproduced HONO at urban and mountain sites, identifying nitrate photolysis and heterogeneous NO2 conversion as primary sources.
• Model failed to replicate daytime HONO at coastal sites, indicating an unidentified marine source correlated with tidal changes.
• HONO significantly contributed to daytime OH production (31–57%) across all sites, especially coastal ones (~50%).

Conclusions:

• An unidentified marine HONO source significantly impacts coastal atmospheric chemistry.
• Ignoring HONO, particularly marine-derived sources, leads to underestimation of radical concentrations and ozone production.
• Highlights critical knowledge gaps in marine atmospheric HONO chemistry requiring further investigation.