**7. Final considerations**

This Chapter provides a review of all relevant historical data concerning the nature, concentrations and impacts of atmospheric aerosols in southeast Brazil. Highlights are the characterization of chemical, physical and optical properties of aerosols, as well as their geographic distribution within the State of São Paulo.

A significant reduction of mean annual PM10 concentrations could be noticed from 1998 onwards, confirming the success of the implementation of stringent air quality control measures, administered by CETESB. However, within the industrial suburb of Cubatão, confined in a valley, concentrations are still about twice the PQAr. After 2002, the annual mean PM10 concentrations in the RMSP and the interior of the state show relatively little year to year variation, but remain mostly below the Annual Standard (PQAr = 50 μg.m-3).

At present, sugar cane burning, together with the re-suspension of soil dust that is inevitable during the harvesting process, is a major influence on aerosol concentrations, size distribution and dry deposition in rural regions of São Paulo State. However, in this region (and elsewhere in Brazil), the practice of pre-harvest burning is being eliminated. Recent legislation (State Law no. 11.241/02) envisages the complete cessation of the practice in mechanizable areas by 2021 and in non-mechanizable areas by 2031. Furthermore, an agreement between sugar cane producers and the State government has been reached, which involves elimination of burning in mechanizable areas by 2014, and in nonmechanizable areas by 2017 [9, 126]. This will have major environmental implications, including improvements in air quality and changes in the rates of deposition of nutrient species from the atmosphere to vegetation, soils and freshwater bodies [10]. Nonetheless, at present burning continues in 44% of the area planted with sugar cane [9]. Tsao *et al.* [127] suggest, using a life cycle analysis, that pollutant emissions in sugar cane regions are still increasing, due an expansion of the planted area, and that the burning step still contributes the largest fraction of the total emission.

Improvements in air quality in the metropolitan regions are likely to proceed at a slower pace than in the interior of the State, largely due to the dominant influence of emissions from the road transport sector. Nonetheless, emissions of aerosols and other pollutants are ultimately expected to be attenuated following progressive modernization of the vehicle fleet, and implementation of better controls on emissions from both vehicular and industrial sources.

Examples of case studies presented have demonstrated the capability of weather radars to detect, track and quantify emissions from biomass fires in the absence of rain echoes, deploying a special elevation scanning procedure to generate Volume-Scans every 7,5 min. Furthermore, satellites orbiting with lidar systems on board (e.g., MODIS-AQUA, CALIPSO, CloudSat) also have the capability to detect and quantify optical properties of aerosols.

With the gradual introduction of lidars in Brazil during recent years, it has also become possible to quantify in situ the vertical distribution and optical properties of suspended aerosols. However, in the State of São Paulo there are currently only three lidar systems available, *viz.*, one fixed lidar each in São Paulo city and in Cubatão, supplemented by the mobile lidar for periodic deployment in the interior of the State. Additional fixed lidar installations are therefore suggested for Campinas, Rio Claro, Bauru and São José do Rio Preto (situated in an important sugar cane production region in the north of the State) as a minimum configuration for a network, together with a second mobile system in São José dos Campos to cover the industrial activities in the Paraiba Valley.
