Distinct Sources and Formation Chemistry of Precipitation Nitrate in Different Antarctic Climates

Abstract

Year-round atmospheric precipitation samples from King George Island (“maritime climate,” Great Wall Station (GWS)) and East Antarctica (“continental climate,” Zhongshan Station (ZS)) were examined to investigate atmospheric nitrate (NO₃⁻) sources and production in different Antarctic climates. In general, the seasonal trends in both concentrations and isotopic composition of NO₃⁻ are weaker at GWS than at ZS. The seasonal variations in δ¹⁵N-NO₃⁻ at both sites suggest shifts in the main sources of NO₃⁻. During the light period (October–April), δ¹⁵N-NO₃⁻ is significantly lower at ZS than at GWS, indicating a primary origin of NO₃⁻ from snow nitrogen oxides emissions driven by NO₃⁻ photolysis. In contrast, midlatitude tropospheric transport and oceanic emissions of alkyl nitrates may play a prominent role at GWS. In the dark period (May–September), stratospheric inputs persist for a shorter time at GWS than at ZS, resulting in lower δ¹⁵N-NO₃⁻ at GWS. Oxygen isotopes (δ¹⁸O and Δ¹⁷O) in precipitation NO₃⁻ are also higher during the dark period than during the light period at both sites. In the light period, NO₃⁻ production is mainly influenced by hydroxyl radicals and peroxyl radicals at GWS, resulting in lower δ¹⁸O- and Δ¹⁷O-NO₃⁻ values than at ZS, where ozone (O₃) plays a more important role in NO₃⁻ formation. In the dark period, significantly higher oxygen isotopic values of NO₃⁻ at ZS than at GWS suggest the more important role of O₃, especially stratospheric O₃, on NO₃⁻ production at ZS. The findings of this study suggest the distinct sources and formation chemistry of atmospheric NO₃⁻ in different Antarctic climates.