An examination of the inorganic chlorine budget in the lower stratosphere

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 (Cl-y) in the lower stratosphere in 1997. We find (ClO + ClONO2 + HCl)/Cl-y = 0.92 +/- 0.10, where Cl-y 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 Cl-y in the lower stratosphere. We find no evidence in support of missing inorganic chlorine species that compose a significant fraction of Cl-y. 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/Cl-y is not significantly controlled by aerosol surface area density in the lower stratosphere.