Mass accommodation: Uptake coefficients of N2O5 on pure water and on NaCl containing droplets. A contribution to subproject HALIPP

Dinitrogen pentoxide (N2O5) is an important constituent in the atmosphere. It plays the role of a night-time reservoir of NO3 radicals. The heterogeneous reactions of N2O5 with aqueous aerosols may convert this reservoir to HNO3 (that is photolysed only slowly in the troposphere). This heterogeneous sink of N2O5 is believed to terminate the reaction cycle of NOx, mainly responsible for the formation of tropospheric ozone. Recently, it has been shown that N2O5 may also react with NaCl salt to form nitryl chloride (ClNO2), a photolytic precursor of the highly reactive atomic chlorine. Behnke and Zetzsch showed that nitryl chloride is also formed in deliquescent aqueous aerosols and even in dilute solutions. With regard to these observations, it appears important to understand the efficiency of the heterogeneous reactions of N2O5 with aqueous surfaces. Therefore, we studied the uptake of N2O5 by water and NaCl solution (at 1 mol/l) using the droplet train technique.