COMPOSITION OF BR-CONTAINING AEROSOLS AND CASES RELATED TO BOUNDARY-LAYER OZONE DESTRUCTION IN THE ARCTIC

During the third Arctic Gas and Aerosol Sampling Program (March 1989), aircraft measurements of atmospheric gases and aerosols were performe d in the European Arctic for the purpose of investigating the phenomen on of boundary layer O-3 destruction. Eight high-volume aerosol filter samples were collected in tropospheric air over the pack ice. In thes e sampling periods, continuous O-3 measurements were made and trace ga ses were collected in flasks. For all samples, total elemental bromine collected on the filters in excess of the estimated sea salt componen t (XSFBr) was found to anticorrelate strongly (r = -0.90) with the mea n ozone concentration observed during the sampling period. These findi ngs are similar to earlier observations at Alert and Barrow. Air sampl es collected during these periods were analysed for Br-containing gase s and hydrocarbons. None of these compounds were well correlated with either O-3 or XSFBr concentration over the course of the experiment. T his is probably because variable conditions of local meteorology, atmo spheric structure and geographic location influenced the degree to whi ch O-3 was depleted, by affecting the size of the reaction reservoir a nd the source(s) of the reactants. Samples collected in the surface (s imilar to 50 m deep) isothermal or slightly stable layer (SSL) over pa ck ice and with light winds from the direction of the central Arctic s howed the highest O-3 depletions. When winds were from the direction o f open water, significantly higher O-3 and lower XSFBr values were obs erved. When the SSL was not present, samples collected below the stron g inversion showed less O-3 destruction and lower XSFBr concentrations than similar low altitude samples collected within the SSL. This is c onsistent with the notion of a larger reservoir volume available for r eaction. Gas and aerosol chemistry results were compared for two sampl es collected close spatially and temporally over ice north of Spitsber gen. Our data indicate that (1) CHBr3 may be the key organobromine spe cies supplying Br atoms and BrO radicals in a heterogeneous photochemi cal reaction cycle causing the photolytic destruction of O-3 in the sp ringtime Arctic surface layers, and (2) ambient hydrocarbons (especial ly C2H2) are depleted during O-3 destruction, and may be important in the overall reaction mechanism. This catalytic O-3 depletion process w as observed to occur to an extent causing near-total O-3 destruction i n the SSL over a 1-2 d period. Thus, relatively rapid photochemical re actions between atmospheric Br, hydrocarbons and aerosols are suggeste d as driving the photolytic O-3 destruction process.