Heterogeneous Reactions of Chlorine Nitrate and Dinitrogen Pentoxide on Sulfuric Acid Surfaces Representative of Global Stratospheric Aerosol Particles

Abstract

AbstractIncreasing evidence from field measurements, modeling studies, and laboratory experiments suggests that heterogeneous reactions on stratospheric sulfate aerosol particles can change the partitioning in the nitrogen and chlorine families and thereby affect global ozone levels. In this study, a Knudsen cell flow reactor was used to measure the uptake of ClONO2 and N2O5 by sulfuric acid solutions representative of background and volcanic stratospheric aerosol particles. The uptake coefficient (γ) of chlorine nitrate on 50–75 wt% H2SO4 at 223 K was found to be markedly dependent on the acid concentration, with γ ranging from about 1 × 10−2 to 1 × 10−4. These results are in good agreement with literature reports and the data fit the expression log γ= 1.87 – 0.074 × (wt% H2SO4). This reaction will thus have its largest impact when stratospheric temperatures are low and sulfuric acid aerosols are most dilute. Uptake of N2O5 was studied on solutions with compositions in the range 58–96 wt% H2SO4 at temperatures from 193 to 303 K. N2O5 reacted readily on sulfuric acid surfaces with uptake coefficients of about 0.06. The uptake coefficient was found to be independent of the sulfuric acid concentration and the solution temperature over the ranges studied. These results suggest that the reaction of N2O5 with H2O will occur readily on sulfuric acid aerosol particles for most stratospheric conditions.