ABSTRACT
Theoretical studies, aircraft, and space-borne measurements show that deep convection can be an effective conduit for
introducing reactive surface pollutants into the free troposphere. The chemical consequences of convective systems are
complex. For example, sensitivity studies show potential for both enhancement and diminution of ozone formation. Field
observations of cloud and mesoscale phenomena have been investigated with the Goddard Cumulus Ensemble and Tropospheric
Chemistry models. Case studies from the tropical ABLE 2, STEP, and TRACE-A experiments show that free
tropospheric ozone formation should increase when deep convection and urban or biomass burning pollution coincide, and
decrease slightly in regions relatively free of ozone precursors (often marine). Confirmation of post-convective ozone enhancement
in the free troposphere over Brazil, the Atlantic, and southern Africa was a major accomplishment of the September–October
1992 TRACE-A (Transport and Atmospheric Chemistry near the Equator—Atlantic) aircraft mission. A flight
dedicated to cloud outflow showed that deep convection led to a factor of 3–4 increase in upper tropospheric ozone formation
downwind. Analysis of ozonesondes during TRACE-A was consistent with 20%–30% of seasonally enhanced ozone
over the South Atlantic being supplied by a combination of biomass burning emissions, lightning, and deep convection over
South America. With the Tropics the critical region for troposphere-to-stratosphere transfer of pollutants, these results have
implications for the total ozone budget. Cloud-scale analyses will guide the development of more realistic regional and
global chemical-transport models to assess the full impact of deep convection on atmospheric chemical composition.
ABSTRACTTheoretical studies, aircraft, and space-borne measurements show that deep convection can be an effective conduit forintroducing reactive surface pollutants into the free troposphere. The chemical consequences of convective systems arecomplex. For example, sensitivity studies show potential for both enhancement and diminution of ozone formation. Fieldobservations of cloud and mesoscale phenomena have been investigated with the Goddard Cumulus Ensemble and TroposphericChemistry models. Case studies from the tropical ABLE 2, STEP, and TRACE-A experiments show that freetropospheric ozone formation should increase when deep convection and urban or biomass burning pollution coincide, anddecrease slightly in regions relatively free of ozone precursors (often marine). Confirmation of post-convective ozone enhancementin the free troposphere over Brazil, the Atlantic, and southern Africa was a major accomplishment of the September–October1992 TRACE-A (Transport and Atmospheric Chemistry near the Equator—Atlantic) aircraft mission. A flightdedicated to cloud outflow showed that deep convection led to a factor of 3–4 increase in upper tropospheric ozone formationdownwind. Analysis of ozonesondes during TRACE-A was consistent with 20%–30% of seasonally enhanced ozoneover the South Atlantic being supplied by a combination of biomass burning emissions, lightning, and deep convection overSouth America. With the Tropics the critical region for troposphere-to-stratosphere transfer of pollutants, these results haveimplications for the total ozone budget. Cloud-scale analyses will guide the development of more realistic regional andglobal chemical-transport models to assess the full impact of deep convection on atmospheric chemical composition.
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