HETEROGENEOUS REACTIONS OF CHLORINE NITRATE AND DINITROGEN PENTOXIDE ON SULFURIC-ACID SURFACES REPRESENTATIVE OF GLOBAL STRATOSPHERIC AEROSOL-PARTICLES

Increasing evidence from field measurements, modeling studies, and lab oratory experiments suggests that heterogeneous reactions on stratosph eric sulfate aerosol particles can change the partitioning in the nitr ogen and chlorine families and thereby affect global ozone levels. in this study, a Knudsen cell flow reactor was used to measure the uptake of CIONO2 and N2O5 by sulfuric acid solutions representative of backg round and volcanic stratospheric aerosol particles. The uptake coeffic ient (gamma) of chlorine nitrate on 50-75 wt% H2SO4 at 223 K was found to be markedly dependent on the acid concentration, with gamma rangin g from about 1 x 10(-2) to 1 x 10(-4). These results are in good agree ment with literature reports and the data fit the expression log gamma = 1.87 - 0.074 x (wt% H2SO4). This reaction will thus have its larges t impact when stratospheric temperatures are low and sulfuric acid aer osols are most dilute. Uptake of N2O5 was studied on solutions with co mpositions in the range 58-96 wt% H2SO4 at temperatures from 193 to 30 3 K. N2O5 reacted readily on sulfuric acid surfaces with uptake coeffi cients of about 0.06. The uptake coefficient was found to be independe nt of the sulfuric acid concentration and the solution temperature ove r the ranges studied. These results suggest that the reaction of N2O5 with H2O will occur readily on sulfuric acid aerosol particles for mos t stratospheric conditions.