HORIZONTAL VISIBILITY INFLUENCE ON THE BRAZILIAN SOLAR ENERGY ASSESSMENT: SURFACE AND MODEL DATA INTERCOMPARSIONS Rodrigo Santos Costa 1,2,3 , Fernando Ramos Martins 2 and Enio Bueno Pereira 2 1 CPTEC/National Institute for Space Research, São José dos Campos, São Paulo (Brazil) 2 CCST/National Institute for Space Research, São José dos Campos, São Paulo (Brazil) 3 Ambidados, Rio de Janeiro, Rio de Janeiro (Brazil) 1. Introduction Several studies indicates that the usage of renewable energy, especially solar, bring economic and social benefits. These benefits are associated with development of remote areas, which are not assisted by Brazilian interconnect energy system from conventional sources; with consequences to stability and planning of Brazilian energy programs to the reduction of direct dependence of fossil fuels and to the direct emission of greenhouse gases in the atmosphere. However, a significant barrier to solar resource expansion as source of energy, to both electricity generation and water heating, is to provide reliable information required to understand available resources and its variability. To the assessment of the solar energy resource, Renewable Energy Group from CPTEC/INPE and CCST/INPE uses the radiative transfer model BRASIL-SR to verify the availability and development of sceneries to this renewable source. The model uses geostationary satellites images and climatological data as input data to parameterize solar radiation interaction processes in atmosphere. The SWERA project (Solar and Wind Energy Resource Assessment), financed by GEF/UNEP, was aimed to provide a consistent and secure environmental database with high reliability and accessibility. The main objective was to motivate the insertion of renewable energies on the electricity matrix of development countries, like Brazil (Pereira et al., 2007). The BRASIL-SR model was used to provide the solar irradiation estimates from 1995 to 2005, what resulted in the publication of Brazilian Solar Energy Atlas (Pereira et al., 2007). The results were quite coherent, being validated by project SONDA stations data and automatic meteorological stations operated in Brazil by CPTEC/INPE. However, when BRASIL-SR parameterize atmospheric aerosols just basing in climatological values of horizontal visibility, the model does not consider important conditions for quantify the amount of atmospheric aerosols in the atmosphere such as biomass burning and pollution sources from megacities and industrial areas. These factors can increase significantly the concentration of particles and greenhouse gases (Raes et al., 2000), specially during dry season. Seasonal variability of meteorological conditions has a direct influence on suspension aerosol amount in the atmosphere. With the beginning of dry station in Brazil Mid-West region, favorable conditions to biomass burning are observed, which can be caused by natural ways or anthropic actions. Besides, the aerosol atmospheric residence time is bigger during the dry season due to the smallest retreat of these aerosols by mixing processes and precipitation (Andrade et al., 2004; Freitas, 2003). Aires and Kirchoff (2001) affirm that the special distribution of biomass burning in Brazil is not uniform, and there is a contrast between source and non-source areas of biomass burning aerosols; related to climatic or regional factors. However, even in areas with less biomass burning, high concentrations of trace gases generated by biomass burning can be found, due to atmospheric transport. The complex influence of aerosols in radiative balance has been evaluated in several studies. It considered up to 80% of biomass burning occurs in the tropics, producing a large amount of gases and particles (Crutzen and Andreae, 1990), affecting the radiative balance (Kaufman and Tanré, 1998; Christopher et al., 2000) and consequently the thermal balance of the atmosphere. Other studies also show indirect effects, through the reduction of the evaporation and precipitation, besides the climatic effects (Ward et al., 1992; Botkin and