Optical and physical properties of aerosols in the boundary layer and free troposphere over the Amazon Basin during the biomass burning season

[摘要] As part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia –Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) campaign, detailedsurface and airborne aerosol measurements were performed over the AmazonBasin during the dry to wet season from 16 September to 14 November 2002.Optical and physical properties of aerosols at the surface, and in theboundary layer (BL) and free troposphere (FT) during the dry season arediscussed in this article. Carbon monoxide (CO) is used as a tracer forbiomass burning emissions. At the surface, good correlation among the lightscattering coefficient (σ_s at 545 nm), PM2.5, and CO indicatesthat biomass burning is the main source of aerosols. Accumulation of hazeduring some of the large-scale biomass burning events led to high PM2.5 (225 μg m⁻³),σ_s (1435 Mm⁻¹), aerosol optical depthat 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 σ_s and aerosol opticalthickness shows that most of the optically active aerosols are confined to alayer with a scale height of 1617 m during the burning season. This isconfirmed by aircraft profiles. The average mass scattering and absorptionefficiencies (545 nm) for small particles (diameter D_p<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 PM2.5aerosols. The observed mean single scattering albedo (ω_o at 545 nm)for submicron aerosols at the surface is 0.92±0.02. The lightscattering by particles (Δσ_s/Δ CN) increase 2–10times from the surface to the FT, most probably due to the combined affectsof coagulation and condensation.

[学科分类] 大气科学