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A macrometrópole Paulista (MMP), conjunto de metrópoles incluindo a Região Metropolitana de São Paulo, com população superior a 33 milhões de habitantes, é uma região crítica do ponto de vista da poluição atmosférica. Foram estudadas propriedades físicas e químicas de aerossóis urbanos na MMP, bem como os processos de formação de aerossóis orgânicos secundários (SOA) por meio de experimentos realizados nos municípios de Diadema, Campinas e São Paulo. Foram utilizadas técnicas como espectrometria de massas de aerossóis e fatoração de matriz positiva. A concentração média de partículas submicrométricas (PM1) foi de 11,3 g/m3 em Diadema, 12,0 g/m3 em Cerqueira César e 13,4 g/m3 em Campinas, sendo predominantemente aerossóis orgânicos (OA) (43% - 58%) e Black Carbon (BC) (14% a 24%). Os sítios de São Paulo (Cerqueira César) e Diadema foram caracterizados pelo impacto de emissões veiculares, enquanto em Campinas verificou-se maior influência de poluição regional e emissões de queimadas. Processos secundários foram responsáveis por 56% da massa total de PM1 em Campinas, 54% em Diadema e 46% em Cerqueira César. Aerossóis da moda de Aitken apresentaram contribuição majoritária de espécies inorgânicas, enquanto a moda de acumulação foi dominada por partículas de BC e SOA. Entre as componentes químicas do aerossol, aerossóis inorgânicos de sulfato e nitrato apresentaram a maior eficiência de espalhamento em massa do PM1. Com relação aos coeficientes de absorção, a contribuição de OA foi quantificada em 23% da absorção total na faixa entre 370 e 880 nm, amplificando a absorção de radiação associada ao BC. The São Paulo macrometropolis (MMP), a group of municipalities around the Metropolitan Region of São Paulo, with a population of more than 33 million inhabitants, is a critical region concerning atmospheric pollution. In this work, physicochemical properties of urban aerosols in MMP were studied, focusing on the mechanisms of production and processing of secondary organic aerosols (SOA), through aerosol mass spectrometry (AMS) and Positive Matrix Factorization (PMF) analysis. The average concentrations of PM1 were 11.3 g/m3 in Diadema, 12.0 g/m3 in Cerqueira César and 13.4 g/m3 in Campinas, dominated by organic aerosol (OA) (43% - 58%) and Black Carbon (BC) (14% to 24%). Diadema and Cerqueira César sampling sites were characterized by a high impact of vehicular emissions. The Campinas site presents more processed aerosols, regional transport, and the impact of biomass burning. The secondary formation was responsible for 54%, 56%, and 46% of the total mass of total PM1 in Diadema, Campinas, and Cerqueira César, respectively. The Aitken mode showed a major contribution from secondary inorganic species of the aerosol. On the other hand, the accumulation mode presented a significant contribution from eBC and OA, mainly from SOA. Among aerosol species, sulfate and nitrate presented the highest mass scattering efficiency. In terms of absorption, the contribution of OA was 23% for absorption coefficients in the 370-880 nm range, which amplifies BC absorption.

The Sao Paulo Metropolitan Area is a unique case worldwide due to the extensive use of biofuel, particularly ethanol, by its large fleet of nearly 8 million cars. Based on source apportionment analysis of Organic Aerosols in downtown Sao Paulo, and using ethanol as tracer of passenger vehicles, we have identified primary emissions from light-duty-vehicles (LDV) and heavy-duty-vehicles (HDV), as well as secondary process component. Each of those factors mirror a relevant primary source or secondary process in this densely occupied area. Using those factors as predictors in a multiple linear regression analysis of a wide range of pollutants, we have quantified the role of primary LDV or HDV emissions, as well as atmospheric secondary processes, on air quality degradation. Results show a significant contribution of HDV emissions, despite contributing only about 5% of vehicles number in the region. The latter is responsible, for example, of 40% and 47% of benzene and black carbon atmospheric concentration, respectively. This work describes an innovative use of biofuel as a tracer of passenger vehicle emissions, allowing to better understand the role of vehicular sources on air quality degradation in one of most populated megacities worldwide.

International audience; Brazil h i g h l i g h t s Carbonaceous particles dominate PM 2.5 concentrations in S~ ao Paulo. Campaign averaged OC:EC ratio for the sampling sites ranged from 0.56 to 1.89. Contribution of secondary OC was estimated around 30e40% for all sites. The OC3 and OC4 fractions depict a more regional behavior across sampling sites. The OC1 fraction is identified to be more dependent of local sources. a b s t r a c t The S~ ao Paulo Metropolitan Area (SPMA) is a megacity with about 20 million people and about 8 million vehicles, most of which are fueled with a significant fraction of ethanol-making it a unique case worldwide. This study presents organic and elemental carbon measurements using thermal-optical analysis from quartz filters collected in four sampling sites within the SPMA. Overall Organic Carbon (OC) concentration was comparable at all sites, where Street Canyon had the highest concentration (3.37 mg m À3) and Park site the lowest (2.65 mg m À3). Elemental Carbon (EC), emitted as result of incomplete combustion, has been significantly higher at the Street Canyon site (6.11 mg m À3) in contrast to all other three sites, ranging from 2.25 mg m À3 (Downtown) to 1.50 mg m-3 (Park). For all sampling sites, the average OC:EC ratio are found on the lower bound (