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

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 NO_x conversion pathways to nitrate, and it can be more sensitive to the change of radical chemistry related to atmospheric oxidation.