Assessment of biomass burnings activity with the synergy of sunphotometric and LIDAR measurements in São Paulo, Brazil

Abstract

In the period of July–November of 2007 an aerosol profiling campaign was carried out with a backscattering LIDAR system in São Paulo, Brazil (23° 33′S, 46° 44′W). The goals of this campaign were to perform an aerosol long period observation in the lower atmosphere (up to 10km) and extract correlations among the microphysical properties obtained from different plataforms, as well to pinpoint events where strong indications of biomass burning plumes were present above the planetary boundary layer (PBL) and still impact quality reports emitted by ground stations provided by the local environmental agency. In this context the present study aims to investigate the impact that this type of aerosol has on the environment of São Paulo when active fires in South America are observed in close and remote areas. Besides the LIDAR system, an AERONET Sunphotometer was used to help in characterizing the aerosol optical properties. Ten cases were selected as an identification of biomass burning layer entrance and after they were confirmed by NOAA-12 AVHRR sensor and 5-day Hysplit generated backtrajectories. A statistical analysis was carried out for analysis of the extinction-to-backscattering ratio (LIDAR ratio — LR) together with the sunphotometer retrieved Angström Exponent (AE) and aerosol optical depth (AOD) data. The observed layer sources were potentially from remote regions as the South Amazon basin and the north portion of Argentina and closer parts of São Paulo state related to sugar cane harvesting activities. The biomass burning plume heights were between 3 and 8km. It has been found that LR, AE and AOD values ranged from 44 to 147sr, from 0.85 to 1.58 and from 0.14 to 0.53, respectively. In a case study for September 7, 2007, an air mass with influence of biomass burning reached the city of São Paulo leading to a LR of 59sr. Despite the AOD value of 0.33, the aerosol size distribution analysis showed a higher amount of fine particulate matter in relation to coarse that is an indicative of transport of material in the free atmosphere. The analysis carried out in this study shows that these plumes affect greatly the LR mean values while with low effect on the AOD and AE daily averages.