Tropospheric ozone and aerosol distributions across the Amazon Basin

Ozone and aerosol distributions were measured during July–August 1985 over the tropical rain forest of Brazil as part of the NASA Global Tropospheric Experiment to study the Amazon boundary layer. Remote and in situ measurements of O 3 and aerosols were made from a NASA Electra aircraft on several long‐range flights spanning different areas between Tabatinga and Belem, Brazil. Continuous O 3 distributions were obtained between the aircraft altitude and the ground with an airborne differential absorption lidar (DIAL) system. Aerosol distributions were also continuously measured above and below the aircraft with the DIAL system. In situ O 3 measurements were made on the aircraft and from ground‐launched ozonesondes at Manaus and Natal. Large‐scale variations in the vertical and horizontal distributions of O 3 and aerosols were observed on nearly all flights over the Amazon Basin, with O 3 exceeding 50 parts per billion by volume (ppbv) in some regions. Both positive and negative correlations were observed between O 3 mixing ratios and aerosol concentrations. In nearly all cases, when O 3 and aerosols were negatively correlated, this represented clean midtropospheric air, and when they were positively correlated, the air mass had undergone photochemical O 3 production as a result of biomass burning. A 59% increase in the planetary boundary layer (PBL) O 3 level was observed between the initial Manaus‐Belem flights on July 23–24, 1985 and the later flights on August 8–9, 1985. This was attributed to the increase in biomass burning near the Rio Amazonas and its tributaries and in savannah regions south of the Amazon Basin. Flights to the west of Manaus measured enhanced O 3 and aerosol levels near the Rio Solimões, while the area sampled upwind of the river exhibited lower O 3 levels. This was explained by the increased incidence of biomass burning near the river. This paper also examines the variability of the trade wind inversion (TWI) height across the Amazon Basin and the influence of O 3 levels above the TWI on the budget of O 3 in the PBL. Measurements reported for the early dry season characterize the background distribution of O 3 and aerosols in the PBL prior to the onset of extensive biomass burning. These data provide the basis for a basin‐scale estimate of photochemical O 3 production from biomass‐burning emissions.