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Os aerossóis atmosféricos respondem por uma das maiores incertezas na investigação dos cenários de mudança climática. A margem de erro associada às estimativas nas contribuições dos aerossóis no balanço energético global ainda é elevada, particularmente no que diz respeito ao chamado "efeito indireto". Ainda que o nível de compreensão científico, acerca do efeito indireto tenha avançado significativamente nos últimos anos, este ainda é muito baixo, quando comparado com o entendimento que se tem do papel dos gases de efeito estufa. Particularmente no Brasil, as medidas realizadas dentro do contexto LBA-SMOCC-EMfiN! (Large-Scale Biosphere-Atmosphere Experiment in Amazonia - Smoke Aerosols, Clouds, Rainfall and Climate - Experimento de Microfísica de Nuvens) possibilitaram uma base de dados ampla sobre aerossóis e microfísica de nuvens. Neste trabalho, apresentamos uma revisão de alguns dos principais resultados relacionados a essa base de dados, tanto via análise de resultados experimentais, quanto via modelagem numérica. Conclui-se que alterações significativas no processo de desenvolvimento da precipitação podem ocorrer em associação com a grande quantidade de aerossóis produzidos em queimadas, mas que diversas questões, principalmente referentes ao papel dos núcleos de condensação gigantes e núcleos de gelo ainda precisam ser elucidadas.Atmospheric aerosols account for some of the largest uncertainties regarding climate change scenarios. The uncertainties associated to the estimates of the aerosol contributions in the global energy budget is still very high, particularly concerning the so-called "indirect effect". Hence, although the level of scientific understanding on the role of aerosols in climate have advanced significantly in the last few years, it is still very low in comparison to the well established knowledge concerning the effect of greenhouse gases. Particularly in Brazil, the measurements taken during the LBA-SMOCC-EMfiN! (Large-Scale Biosphere-Atmosphere Experiment inAmazonia - SmokeAerosols, Clouds, Rainfall and Climate - Experimento de Microfísica de Nuvens) provided a comprehensive data base on aerosols and cloud microphysics. In this work, we review some of the major results related to such data base, via both analysis of experimental data and numerical modeling. We conclude that significant changes in precipitation development may occur in association with the large amount of aerosols launched into the atmosphere by forest fires but that several questions, especially those ones concerning giant cloud condensation nuclei and ice nuclei, have to be clarified.

Air quality conditions in many urban areas have improved in the last decades as a consequence of air pollution control policies and regulations. Mitigation strategies have been successful in reducing the concentration of primary pollutants like inhalable particulate matter (PM10), but the control of secondary pollutants like tropospheric ozone (O3) is still challenging in megacities like the Metropolitan Area of São Paulo (MASP) in Brazil. To support the development of effective mitigation strategies, it is crucial to characterize the statistical behavior of air pollutant concentrations and its long-term evolution. Probability Density Functions (PDF) can be useful to model site-specific air quality conditions, providing estimates for the frequency of extreme pollution events and exceedance of air quality standards. The current study aims to characterize which PDF model better fits and characterizes the variability of PM10 and O3 concentrations in the MASP. For that, daily maximum moving average concentrations were analyzed between 2000 and 2023, characterizing the long-term trends and the frequency of exceedance of air quality standards. PM10 concentrations followed a lognormal PDF, with an expected value of 31 ± 15 µg.m-3. O3 followed a Gamma PDF, with an expected value of 68 ± 25 µg.m-3. A consistent long-term decrease was observed for PM10 (-1.04 ± 0.09 µg.m-3.yr-1), while O3 showed an increasing trend of 0.51 ± 0.04 µg.m-3.yr-1 in the summer. In recent years (2021-2023), the probability of exceedance of the World Health Organization guideline was 17.4 and 11.0%, respectively, for PM10 and O3. In 2020, a statistically significant increase in O3 expected values was observed, possibly associated with changes in the emission patterns of precursors due to the mobility restrictions imposed by the COVID-19 pandemic.