The reaction probabilities of ClONO2 and N2O5 on 40 to 75% sulfuric acid solutions

Abstract

A wetted‐wall flow tube was used to measure the reaction probabilites, γ, of ClONO 2 and N 2 O 5 on sulfuric acid surfaces. The reaction probabilities were determined from first‐order wall loss rate coefficients measured over sulfuric acid slowly flowing down the inside wall of the flow tube. Sulfuric acid content was varied from 40 to 75% by weight, and measurements were conducted at temperatures characteristic of the stratosphere. We determined the reaction probabilities of N 2 O 5 to be 0.12±0.03 over 40% acid at 215 K, 0.14±0.03 over 60% acid at 215 K and 0.10±0.02 over 70 and 75% acid at 220 and 230 K, respectively. The γ for ClONO 2 increased from 2×10−4 over 75% acid at 230 K to 6.4×10−2 over 40% acid at 215 K; these are a factor of 2 lower than a previous determination performed under the same conditions. When we introduced HCl into the flow tube, we detected negligible uptake over the 65 and 70% acid solutions, γ < 3 × 10−5, and a small uptake, γ = 4 × 10−4, for HCl onto 60% acid at 215 K. We did not detect a significant enhancement in the first‐order loss rate coefficients for ClONO 2 over these solutions in the presence of HCl. Thus the reaction ClONO 2 + HCl occurring on 40–75 wt. % sulfuric acid solutions will not be a significant source of activated chlorine in the stratosphere; however, loss of N 2 O 5 and ClONO 2 could affect the NOx and ClOx concentrations.