Influence of local photochemistry on isotopes of nitrate in Greenland snow

Abstract

To explore the seasonality in δ 15 N and δ 18 O of nitrate in Greenland snow, we describe a simple box model of local photochemistry. Isotope ratios of HNO 3 are controlled by the nitrogen isotope fractionation between NO and NO 2 , the ratio of NO 2 to NO, and seasonal variations in HNO 3 production. The observed seasonal range in δ 15 N requires either a large net fractionation (∼70‰) associated with NO x cycling or a seasonal change in the δ 15 N of NO x sources. The observed range in δ 18 O of nitrate is smaller than that calculated from HNO 3 production pathways, suggesting that seasonal transport may also be required to explain the seasonality in nitrate δ 18 O.