IMPACT OF BIOMASS BURNING EMISSIONS ON THE COMPOSITION OF THE SOUTH-ATLANTIC TROPOSPHERE - REACTIVE NITROGEN AND OZONE

In September/October 1992 an instrumented DC-8 aircraft was employed t o study the composition and chemistry of the atmosphere over the south ern tropical Atlantic Ocean. Analysis of measurements, which included tracers of biomass combustion and industrial emissions, showed that th is atmosphere was highly influenced by biomass burning emissions from the South American and African continents. Marine boundary layer was g enerally capped off by a subsidence inversion and its composition to a large degree was determined by slow entrainment from aloft. Insoluble species (such as PAN, NO, hydrocarbons, CO) were enhanced throughout the troposphere. Soluble species (such as HNO3, HCOOH, H2O2) were mini mally elevated in the upper troposphere in part due to scavenging duri ng cloud (wet) convection. Ozone mixing ratios throughout the South At lantic basin were enhanced by approximate to 20 ppb. These enhancement s were larger in the eastern South Atlantic (African emissions) compar ed to the western South Atlantic (South American emissions). In much o f the troposphere, total reactive nitrogen (NOy) correlated well with tracers of biomass combustion (e.g., CH3Cl, CO). Although NOx (NO + NO 2) correlated reasonably with these tracers in the lower (0-3 km) and middle troposphere (3-7 km), these relationships deteriorated in the u pper troposphere (7-12 km). Stratospheric intrusions were found to be a minor source of upper tropospheric NOx or HNO3. Sizable nonsurface s ources of NOx (e.g., lightning) as well as secondary formation from th e NOy reservoir species (such as HNO3, PAN, and organic nitrates) must be invoked to explain the NOx abundance present in the upper troposph ere. It is found that HNO3, PAN, and NOx were able to account for most of the NOy in the middle troposphere (3-7 km); but a significant shor tfall was present in the upper troposphere (7-12). This shortfall was also most pronounced in air masses with low HNOy. The reasons for the upper tropospheric reactive nitrogen shortfall is probably due to inst rumental uncertainties and the presence of unidentified organic and in organic nitrogen species.