Aerosol profiling with lidar in the Amazon Basin during the wet and dry season

Abstract

For the first time, multiwavelength polarization Raman lidar observations of optical and microphysical particle properties over the Amazon Basin are presented. The fully automated advanced Raman lidar was deployed 60km north of Manaus, Brazil (2.5S, 60W) in the Amazon rain forest from January to November 2008. The measurements thus cover both the wet season (Dec-June) and the dry or burning season (July-Nov). Two cases studies of young and aged smoke plumes are discussed in terms of spectrally resolved optical properties (355, 532, and 1064nm) and further lidar products such as particle effective radius and single-scattering albedo. These measurement examples confirm that biomass burning aerosols show a broad spectrum of optical, microphysical, and chemical properties. The statistical analysis of the entire measurement period revealed strong differences between the pristine wet and the polluted dry season. African smoke and dust advection frequently interrupt the pristine phases during the wet season. Compared to pristine wet season conditions, the particle scattering coefficients in the lowermost 2km of the atmosphere were found to be enhanced, on average, by a factor of 4 during periods of African aerosol intrusion and by a factor of 6 during the dry (burning) season. Under pristine conditions, the particle extinction coefficients and optical depth for 532nm wavelength were frequently as low as 10-30 Mm -1 and <0.05, respectively. During the dry season, biomass burning smoke plumes reached to 3-5km height and caused a mean optical depth at 532nm of 0.26. On average during that season, particle extinction coefficients (532nm) were of the order of 100 Mm -1 in the main pollution layer (up to 2km height). ngstrm exponents were mainly between 1.0 and 1.5, and the majority of the observed lidar ratios were between 50-80sr. © 2012. American Geophysical Union. All Rights Reserved.