Changes in atmospheric oxidants over Arctic Ocean atmosphere: evidence of oxygen isotope anomaly in nitrate aerosols

Abstract

Oxygen isotope anomaly of nitrate aerosol (∆17O-NO3−) contributes to understanding the atmospheric nitrogen chemistry in the polar oceans. Here, ∆17O-NO3− of the aerosol samples was analyzed based on a cruise from East Asia to the Arctic Ocean to explore the nitrate formation mechanisms. ∆17O-NO3− decreased with the increase of latitude, especially when after entering the Arctic Circle. ∆17O-NO3− (e.g., 11.5‰–21.2‰) was extremely low while crossing the sea ice-covered Arctic Ocean. This is most likely influenced by the combined enhancement of hydroxyl (OH) and peroxy (HO2 + RO2) radicals derived by sea ice under permanent sunlight period. In addition, the obvious increase in the ∆17O-NO3− of return trip with shortened daytime indicated the advantage of nocturnal pathways (NO3 related) with the higher ∆17O endmembers. The mutation of ∆17O-NO3− can reflect the change of NOx conversion pathways to nitrate, and it can be more sensitive to the change of radical chemistry related to atmospheric oxidation.