An intercomparison of four regional air quality models is performed in the tropical megacity of São Paulo with the perspective of developing a forecasting system based on a model ensemble. Modeled concentrations of the main regulated pollutants are compared with combined observations in the megacity center, after analyzing the spatial scale of representativeness of air monitoring stations. During three contrasting periods characterized by different types of pollution events, the hourly concentrations of carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO₂), and particulate matter (PM_2.5 and PM₁₀) modeled by the ensemble are in moderate agreement with observations. The median of the ensemble provides the best performance (R ≈ 0.7 for CO, 0.7 for NOx, 0.5 for SO₂, 0.5 for PM_2.5, and 0.4 for PM₁₀) because each model has periods and pollutants for which it has the best agreement. NOx concentration is modeled with a large inter‐model variability, highlighting potential for improvement of anthropogenic emissions. Pollutants transported by biomass burning events strongly affect the air quality in São Paulo and are associated with significant inter‐model variability. Modeled hourly concentration of ozone (O₃) is overestimated during the day (≈20 ppb) and underestimated at night (≈10 ppb), while nitrogen dioxide (NO₂) is overestimated at night (≈20 ppb). The observed O₃ concentration is best reproduced by the median of the ensemble (R ≈ 0.8), taking advantage of the variable performance of the models. Therefore, an operational air quality forecast system based on a regional model ensemble is promising for São Paulo.

The 2020 biomass burning season in Brazil was marked by an atypical amount of fire across the Pantanal biome, which led to high levels of smoke within the biome and downwind areas. The present study analyzes fire counts and smoke over Pantanal in 2020, comparing this particular year's data with those from the previous 17 years (2003–2019). Taking as reference the most-polluted years in this period, the regional smoke plume and its impact on surface solar radiation were also evaluated. In 2020, the regional smoke plume core covered an area of ∼ 2.6×10⁶ km² at the peak of the burning season, an area well above that of the previous 6 years but smaller than areas observed in a more remote past, as in 2007 and 2010 (> 5.0×10⁶ km²). The smoke loading was lower (mean aerosol optical depth, AOD, of 550 nm; ∼ 0.7) than that of 2007 and 2010 (mean AOD 550 nm; ∼ 1.0). The plume radiation absorption efficiency, when compared with the previous year's plumes, did not present significant differences. Regarding the Pantanal burning season, it revealed some atypical features. Fire counts were up to 3.0 times higher than for the years from 2003 to 2019. Smoke loading over Pantanal, which is typically a fraction of that over Amazonia, was higher in 2020 than that over Amazonia, an indication that local smoke surpassed the smoke advection from upwind regions. The observed intraseasonal variability in smoke over Pantanal revealed to be largely driven by the nature of the burned areas in the biome. From September on, there was a significant increase in fire count in conservation and indigenous areas, where higher biomass density is present, which would explain the larger smoke plumes over Pantanal, even during October when the fire count was reduced. In October, the biome was covered by a thick smoke layer, which resulted in a mean deficit of surface solar radiation up to 200 W m⁻². Despite the Pantanal biomes' massive burning in 2020, the regional smoke plume was not far from its climatological features. Nevertheless, the Pantanal 2020 burning season represents the worst combination of a climate extreme applied to a fire-prone environment, coupled with inadequately enforced environmental regulations, from which there is much to be learned.

Smoke aerosol plumes generated during the biomass burning season in Brazil suffer long-range transport, resulting in large aerosol optical depths over an extensive domain. As a consequence, downward surface solar irradiance, and in particular the direct component, can be significantly reduced. Accurate solar energy assessments considering the radiative contribution of biomass burning aerosols are required to support Brazil’s solar power sector. This work presents the 2nd generation of the radiative transfer model BRASIL-SR, developed to improve the aerosol representation and reduce the uncertainties in surface solar irradiance estimates in cloudless hazy conditions and clean conditions. Two numerical experiments allowed to assess the model’s skill using observational or regional MERRA-2 reanalysis AOD data in a region frequently affected by smoke. Four ground measurement sites provided data for the model output validation. Results for DNI obtained using $\delta$-Eddington scaling and without scaling are compared, with the latter presenting the best skill in all sites and for both experiments. An increase in the relative error of DNI results obtained with $\delta$-Eddington optical depth scaling as AOD increases is evidenced. For DNI, MBD deviations ranged from −2.3 to −0.5%, RMSD between 2.3 and 4.7% and OVER between 0 and 5.3% when using in-situ AOD data. Overall, our results indicate a good skill of BRASIL-SR for the estimation of both GHI and DNI.

Air pollution in the Metropolitan Area of São Paulo (MASP), Brazil, is a serious problem and is strongly affected by local sources. However, atmosphere column composition in MASP is also affected by biomass burning aerosol (BB). Understanding the impacts of aerosol particles, from both vehicles and BB, on the air quality and climate depends on in-depth research with knowledge of some parameters such as the optical properties of particles and their chemical composition. This study characterized fine particulate matter (PM_2.5) from July 2019 to August 2020 in the eastern part of the MASP, relating the chemical composition data obtained at the surface and columnar optical parameters, such as aerosol optical depth (AOD), Ångström Exponent (AE), and single-scattering albedo (SSA). According to the analyzed data, the mean PM_2.5 concentration was 18.0 ± 12.5 µg/m³; however, daily events exceeded 75 times the air quality standard of the World Health Organization (15 µg/m³). The mean black carbon concentration was 1.8 ± 1.5 µg/m³ in the sampling period. Positive matrix factorization (PMF) identified four main sources of aerosol: heavy vehicles (42%), followed by soil dust plus local sources (38.7%), light vehicles (9.9%), and local sources (8.6%). AOD and AE presented the highest values in the dry period, during which biomass burning events are more frequent, suggesting smaller particles in the atmosphere. SSA values at 440 nm were between 0.86 and 0.94, with lower values in the winter months, indicating the presence of more absorbing aerosol.

A poluição atmosférica gerada pelas atividades antrópicas afeta tanto o equilíbrio climático quanto a qualidade do ar. O Material Particulado (MP) é reconhecidamente o poluente atmosférico com maior impacto na saúde humana. No estado de São Paulo, as principais fontes de MP são as emissões veiculares, nas áreas urbanas, e a queima de biomassa, nas áreas rurais. Com o objetivo de mitigar a poluição nas áreas rurais, em 2007 foi assinado o protocolo agroambiental entre o estado de São Paulo e o setor sucroalcooleiro, o qualtrata da redução e da eliminação gradual do uso da queima como prática de colheita de cana até 2017. A análise da tendência nos níveis dos poluentes atmosféricos no estado é fundamental para a avaliação dos resultados do protocolo. Entretanto, apesar de apresentar a maior rede de monitoramentode qualidade do ar no Brasil, São Paulo não tem monitoramento da poluição atmosférica na maioria dos seus municípios. Nesse contexto, visando avaliar o impacto do protocolo agroambiental, o presente estudo analisou a distribuição espacial e temporal da profundidade óptica do aerossol (AOD) no estado entreos anos de 2007 (quando o protocolo foi assinado) e 2017. AOD é um indicador óptico da abundância do MP na atmosfera, derivado das medidas de radiância espectral do sensor MODIS a bordo do satélite Terra. Os resultados revelaram que, quando a influência do transporte de fumaça das regiões Norte e Centro-Oeste do Brasil é removida, os dados de satélite identificam adequadamente as regiões mais poluídas no estado: as áreas metropolitanas de São Paulo, de Campinas e da Baixada Santista e as porções central e norte, que são dominadas pelas plantações de cana-de-açúcar. Em relação à tendência depoluição, nas áreas a oeste e noroeste do estado, onde ocorreu expansão do cultivo de cana nos últimos anos, apesar das limitações impostas para queima pelo protocolo agroambiental, observou-se tendência significativa de aumento da poluição. Já nas áreas de tradicional cultivo de cana, nas porçõescentro e norte do estado, embora se tenha percebido tendência de redução da poluição associada ao MP, ela não foi significativa.

A poluição do ar é um dos principais problemas enfrentados em regiõesurbanas, e sua percepção pela população é fundamental para a mitigaçãodo problema. Este estudo analisou a percepção da poluição do ar por doisgrupos de comerciários do município de Diadema: um atuante no centro dacidade, em uma via de intenso tráfego, e outro atuante na periferia (bairro).Os resultados demonstram que os entrevistados têm clara percepção dapoluição do ar (90% no centro e 70% no bairro) e identificaram corretamenteseu principal agente, a emissão veicular. Entretanto, a maioria dosentrevistados (65%) não se identificou como causa do problema. A percepçãodos entrevistados sobre a evolução da qualidade do ar foi coerente com dadosde concentração dos poluentes. Vale ressaltar a divergência encontradaentre a percepção dos comerciários e os índices oficiais de qualidade do ar.Não houve diferenças significativas entre as percepções dos comerciários docentro e do bairro.