Optical and physical properties of aerosols in the boundary layer and free troposphere over the Amazon Basin during the biomass burning season D. Chand1,*, P. Guyon1, P. Artaxo2, O. Schmid1,**, G. P. Frank1, L. V. Rizzo2, O. L. Mayol-Bracero3, L. V. Gatti4, and M. O. Andreae1 1Max Planck Institute for Chemistry, Mainz, Germany 2Institute of Physics, University of São Paulo, São Paulo, Brazil 3University of Puerto Rico, San Juan, PR, USA 4Institute of Nuclear Energy Research, São Paulo, Brazil *now at: University of Washington-Bothell, Bothell, USA **now at: GSF-Research Center for Environment and Health, Neuherberg/Munich, Germany
Abstract. As part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia –
Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) campaign, detailed
surface and airborne aerosol measurements were performed over the Amazon
Basin during the dry to wet season from 16 September to 14 November 2002.
Optical and physical properties of aerosols at the surface, and in the
boundary layer (BL) and free troposphere (FT) during the dry season are
discussed in this article. Carbon monoxide (CO) is used as a tracer for
biomass burning emissions. At the surface, good correlation among the light
scattering coefficient (σs at 545 nm), PM2.5, and CO indicates
that biomass burning is the main source of aerosols. Accumulation of haze
during some of the large-scale biomass burning events led to high PM2.5 (225 μg m−3),
σs (1435 Mm−1), aerosol optical depth
at 500 nm (3.0), and CO (3000 ppb). A few rainy episodes reduced the PM2.5,
number concentration (CN) and CO concentration by two orders of magnitude.
The correlation analysis between σs and aerosol optical
thickness shows that most of the optically active aerosols are confined to a
layer with a scale height of 1617 m during the burning season. This is
confirmed by aircraft profiles. The average mass scattering and absorption
efficiencies (545 nm) for small particles (diameter Dp<1.5 μm)
at surface level are found to be 5.0 and 0.33 m2 g−1,
respectively, when relating the aerosol optical properties to PM2.5
aerosols. The observed mean single scattering albedo (ωo at 545 nm)
for submicron aerosols at the surface is 0.92±0.02. The light
scattering by particles (Δσs/Δ CN) increase 2–10
times from the surface to the FT, most probably due to the combined affects
of coagulation and condensation.
Citation: Chand, D., Guyon, P., Artaxo, P., Schmid, O., Frank, G. P., Rizzo, L. V., Mayol-Bracero, O. L., Gatti, L. V., and Andreae, M. O.: Optical and physical properties of aerosols in the boundary layer and free troposphere over the Amazon Basin during the biomass burning season, Atmos. Chem. Phys., 6, 2911-2925, doi:10.5194/acp-6-2911-2006, 2006.