An examination of the inorganic chlorine budget in the lower stratosphere

Abstract

We use the first simultaneous in situ measurements of ClONO2, ClO, and HCl acquired using the NASA ER‐2 aircraft during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission to test whether these three compounds quantitatively account for total inorganic chlorine (Cly) in the lower stratosphere in 1997. We find (ClO + ClONO2 + HCl)/Cly = 0.92±0.10, where Cly is inferred from in situ measurements of organic chlorine source gases. These observations are consistent with our current understanding of the budget and partitioning of Cly in the lower stratosphere. We find no evidence in support of missing inorganic chlorine species that compose a significant fraction of Cly. We apply the analysis to earlier ER‐2 observations dating from 1991 to investigate possible causes of previously observed discrepancies in the inorganic chlorine budget. Using space shuttle, satellite, balloon, and aircraft measurements in combination with ER‐2 data, we find that the discrepancy is unlikely to have been caused by missing chlorine species or an error in the photolysis rate of chlorine nitrate. We also find that HCl/Cly is not significantly controlled by aerosol surface area density in the lower stratosphere.