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 (NO 3 − ) sources and production in different Antarctic climates. In general, the seasonal trends in both concentrations and isotopic composition of NO 3 − are weaker at GWS than at ZS. The seasonal variations in δ 15 N‐NO 3 − at both sites suggest shifts in the main sources of NO 3 − . During the light period (October–April), δ 15 N‐NO 3 − is significantly lower at ZS than at GWS, indicating a primary origin of NO 3 − from snow nitrogen oxides emissions driven by NO 3 − 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 δ 15 N‐NO 3 − at GWS. Oxygen isotopes (δ 18 O and Δ 17 O) in precipitation NO 3 − are also higher during the dark period than during the light period at both sites. In the light period, NO 3 − production is mainly influenced by hydroxyl radicals and peroxyl radicals at GWS, resulting in lower δ 18 O‐ and Δ 17 O‐NO 3 − values than at ZS, where ozone (O 3 ) plays a more important role in NO 3 − formation. In the dark period, significantly higher oxygen isotopic values of NO 3 − at ZS than at GWS suggest the more important role of O 3 , especially stratospheric O 3 , on NO 3 − production at ZS. The findings of this study suggest the distinct sources and formation chemistry of atmospheric NO 3 − in different Antarctic climates.