Redistribution by deep convection and long‐range transport of CO and CH4 emissions from the Amazon basin, as observed by the airborne campaign TROPOZ II during the wet season

Abstract

Flights performed over South America in the Austral summer, during the airborne campaign Tropospheric Ozone Experiment (TROPOZ II, January 1991), have shown an upper tropospheric maximum (UTM) of carbon monoxide, methane, and relative humidity above 7 km altitude and between 30°S and 5°N. The study of chemical characteristics and convective/transport processes associated with this UTM shows that the air came from the Amazon basin boundary layer, was lifted by convective processes to upper levels, and was then redistributed over South America, and even across the South Atlantic toward the African coast, by the upper level anticyclone present during the wet season over tropical South America. The chemical composition of this UTM (high CO, CH4, and relative humidity; medium NOy, NO, and alkanes; low ozone and acetylene) agrees with the observations from the Atmospheric Boundary Layer Expedition ABLE 2B over the Amazon basin during the wet season and supports a biogenic origin for methane and carbon monoxide. The slow (or even absent) photochemical activity associated with this UTM can be explained by the low levels of active hydrocarbons and reactive nitrogen species. The TROPOZ II results complete and extend observations from previous expeditions by demonstrating that large biogenic emissions of ozone precursors from the Amazon basin can enter the upper general circulation during the Austral summer (December‐January‐February) and, though they do not contribute significantly to the ozone budget over South America, on being exported to the rest of the global circulation they will certainly become involved in the global ozone budget.