A. S. Procopio

The effects of biomass burning aerosols and clouds on the CO2 flux in Amazonia

Aerosol particles associated with biomass burning emissions affect the surface radiative budget and net ecosystem exchange (NEE) over large areas in Amazonia during the dry season. We analysed CO2 fluxes as a function of aerosol loading for two forest sites in Amazonia as part of the LBA experiment. Aerosol optical thickness (AOT) measurements were made with AERONET sun photometers, and CO2 flux measurements were determined by eddy-correlation. The enhancement of the NEE varied with different aerosol loading, as well as cloud cover, solar elevation angles and other parameters. The AOT value with the strongest effect on the NEE in the FLONA-Tapajós site was 1.7, with an enhancement of the NEE of 11% compared with clear-sky conditions. In the RBJ site, the strongest effect was for AOT of 1.6 with an enhancement of 18% in the NEE. For values of AOT lager than 2.7, strong reduction on the NEE was observed due to the reduction in the total solar radiation. The enhancement in the NEE is attributed to the increase of diffuse versus direct solar radiation. Due to the fact that aerosols from biomass burning are present in most tropical areas, its effects on the global carbon budget could also be significant.

Química atmosférica na Amazônia: a floresta e as emissões de queimadas controlando a composição da atmosfera amazônica

The understanding of the natural processes that regulate atmospheric composition in Amazonia is critical to the establishment of a sustainable development strategy in the region. The large emissions of trace gases and aerosols during the dry season, as a result of biomass burning, profoundly change the composition of the atmosphere in most of its area. The concentration of trace gases and aerosols increases by a factor of 2 to 8 over large areas, affecting the natural mechanisms of several key atmospheric processes in the region. Cloud formation mechanisms, for instance, are strongly affected when the concentration of cloud condensation nuclei (CCN) changes from 200-300 CCN/cc in the wet season to 5,000-10,000 CCN/cc in the dry season. The cloud droplet radius is reduced from values of 18 to 25 micrometers in the wet season to 5 to 10 micrometers in the dry season, suppressing cloud formation and the occurrence of precipitation under some conditions. Ozone is a key trace gas for changes in the forest health, with concentrations increasing from 12 parts per billion (ppb), at the wet season, to values as high as 100 ppb (in the dry season in areas strongly affected by biomass burning emissions). At this level, ozone could be damaging the vegetation in regions far from the emissions. The atmospheric radiation balance is also strongly affected, with a net loss of up to 70% of photosynthetic active radiation at the surface.

Direct and Semi‐Direct Aerosol Effects: a Modeled Study for Biomass Burning Aerosol Radiative Forcing in the Amazon Region

The effect of clouds on aerosol radiative forcing is examined by means of simulations considering the presence of a cloud layer above a homogeneous biomass burning aerosol layer. The forcings were calculated considering that aerosols can reduce cloud formation, the semi‐direct effect. A comparison of these results with the forcings calculated for clear sky condition shows that aerosol radiative forcing can be significantly altered by the semi‐direct effect, suggesting that this should be considerate in further studies of regional climate change.

A Study of the Spatial Distribution of Aerosol Optical Thickness in Rio de Janeiro

The Rio de Janeiro Metropolitan Region (RJMR) has the second largest concentration of people, vehicles, industries and other air pollutant sources of Brazil, suffering from chronic air pollution problems. A high resolution (1×1 km) spatial distribution of aerosols over the RJMR was obtained based on reflectance measured by MODIS (Moderate Resolution Spectrometer) sensors, on board of EOS‐Terra platform, operated by NASA/GSFC. Aerosol optical thicknesses were retrieved from these measurements using the software SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer Model) and an algorithm developed in a previous study.