OZONE DESTRUCTION AND BROMINE PHOTOCHEMISTRY AT GROUND-LEVEL IN THE ARCTIC SPRING

RECENT Arctic field studies in the spring at Alert, Canada (82.5°N, 62.3°W), show that ground-level ozone concentrations fell from 30-40 parts per 109 (p.p.b.) to almost 0 p.p.b. in a period of time ranging from a few hours to a few days (Fig. I)1,2. Simultaneously, the concentration of brominated species collected on cellulose filters increases dramatically, with 50% or more of this bromine attributed to gaseous compounds such as HBr1,3. The dramatic change in surface ozone and increase in filterable bromine seem to be due to advection of air below the inversion layer off the polar ice cap; in this air mass, surface ozone has been depleted and filterable bromine formed from photochemical reactions involving bromine compounds1. Here we report laboratory experiments and computer kinetic modelling studies which indicate that the photochemically active bromine compound may be nitryl bromide (BrNO2), formed in the reaction4 of N2O5 with NaBr found in sea-salt particles. BrNO2 will photolyse rapidly at sunrise, forming ozone-destroying bromine atoms. We propose key field experiments to test this hypothesis. © 1990 Nature Publishing Group.