Abstract
Abstract. We describe a comparison study of Aerosol Optical Thickness (AOT) from numerical simulations using a regional atmospheric model with an elastic backscattering lidar operating at 532 nm and a sunphotometer belonging to the AERONET network at São Paulo (23° S 46° W) city, Brazil, a very populated urban area. The atmospheric model includes an aerosol emission, transport and deposition module coupled to a radiative transfer parameterization, which takes the interaction between aerosol particles and short and long wave radiation into account. A period of one week was taken as case study during the dry season (late August) when intense biomass burning activities occur at remote areas in South America, and meteorological conditions disfavor the pollution dispersion in the city of São Paulo. The situation presented here showed how smoke from biomass burning in remote areas is transported to the south-east part of Brazil and affects the optical atmospheric conditions in São Paulo. The numerical simulations are corroborated by in situ measurements of AOT obtained by lidar and sun photometry.
Highlights
In South America every year during the dry season (July to October) a continental scale biomass burning activity occurs mainly associated to land use change
R corresponds to the resolution binning used to calculate the α and β the values taken in the whole period show that the maximum Aerosol Optical Thickness (AOT) values obtained by CATT-BRAMS and measured by the sunphotometer show some large differences which can be understood from three aspects a) the sunphotometer data taken is level 1.5 and the level 2.0 after calibration could change the AOT values due instrument issues; b) The week during the measurements presented some clouds which are taken into account in the model and c) The grid resolution employed in the model gives an average over an area of 40×40 km2
The CATT-BRAMS simulations have been very useful in assessing the dispersion and transport of biomass burning aerosol over South America
Summary
In South America every year during the dry season (July to October) a continental scale biomass burning activity (vegetation fires) occurs mainly associated to land use change. In same cases, this transport is strongly augmented by occurrence of the South America Low Level Jet, a strong low troposphere pole-ward stream at East side of the Andes (Vera et al, 2006; Longo et al, 2006a,b). The occurrence of other transient systems like mid-latitude cold fronts from the South can change this scenario and prepares corridors of smoke export towards the south-east part of Brazil, where the most populated urban areas do exist In these events, the local air pollution produced by the urban activities gain additional load of pyrogenic and aged aerosols and gases, changing the local air quality and atmospheric optical property patterns. During the so called dry season which corresponds to the period of June through September
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