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One of the least understood aspects in atmospheric chemistry is how urban emissions influence the formation of natural organic aerosols, which affect Earth’s energy budget. The Amazon rainforest, during its wet season, is one of the few remaining places on Earth where atmospheric chemistry transitions between preindustrial and urban-influenced conditions. Here, we integrate insights from several laboratory measurements and simulate the formation of secondary organic aerosols (SOA) in the Amazon using a high-resolution chemical transport model. Simulations show that emissions of nitrogen-oxides from Manaus, a city of ~2 million people, greatly enhance production of biogenic SOA by 60–200% on average with peak enhancements of 400%, through the increased oxidation of gas-phase organic carbon emitted by the forests. Simulated enhancements agree with aircraft measurements, and are much larger than those reported over other locations. The implication is that increasing anthropogenic emissions in the future might substantially enhance biogenic SOA in pristine locations like the Amazon.

Southeastern Brazil, the most populous and developed region of the country, faces various environmental problems associated with the growth of its population in urban areas. It is the most industrialized area in the country, comprising the metropolitan areas of São Paulo, Rio de Janeiro, Belo Horizonte, and other major cities. Air quality is a major concern, because the reported concentrations of certain regulated pollutants, typically ozone and fine particulate, have exceeded national standards. Due to the difficulty in taking measurements over many different areas, air quality modeling is a useful tool to estimate air pollutant concentrations. For southeastern Brazil, air quality modeling has been performed mostly with the Brazilian Regional Atmospheric Modeling System with Simplified Photochemical Module and the Weather Research and Forecast with Chemistry models. One of the main objectives was to study the evolution of air quality associated with improved vehicle emission factors in urban areas, the impact of climate change on air quality, and the relationship between pollutant concentrations and health. Knowledge of mobile source emission factors has been continuously expanded by in-tunnel measurements and dynamometer protocols, which provide accurate data as inputs to photochemical air quality models. The spatial distribution of the mobile source emissions was constructed based on open access data related to the streets and traffic distribution. The mobile emission module was combined to the chemistry modeling and this implementation can be an example to be applied to other places that do not have a spatial distribution of this source. Forecasts of pollutant concentrations can inform public policies, including those addressing the effects of pollutants on health of the general population, and studies of the impacts of using different fuels and implementation of emissions regulations programs.

Abstract. The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in particulate matter vehicular emission profiles. In an effort to better characterise the emitted particulate matter, measurements of aerosol physical and chemical properties were undertaken inside two tunnels located in the São Paulo Metropolitan Area (SPMA). The tunnels show very distinct fleet profiles: in the Jânio Quadros (JQ) tunnel, the vast majority of the circulating fleet are light duty vehicles (LDVs), fuelled on average with the same amount of ethanol as gasoline. In the Rodoanel (RA) tunnel, the particulate emission is dominated by heavy duty vehicles (HDVs) fuelled with diesel (5 % biodiesel). In the JQ tunnel, PM 2.5 concentration was on average 52 µg m −3 , with the largest contribution of organic mass (OM, 42 %), followed by elemental carbon (EC, 17 %) and crustal elements (13 %). Sulphate accounted for 7 % of PM 2.5 and the sum of other trace elements was 10 %. In the RA tunnel, PM 2.5 was on average 233 µg m −3 , mostly composed of EC (52 %) and OM (39 %). Sulphate, crustal and the trace elements showed a minor contribution with 5 %, 1 %, and 1 %, respectively. The average OC : EC ratio in the JQ tunnel was 1.59 ± 0.09, indicating an important contribution of EC despite the high ethanol fraction in the fuel composition. In the RA tunnel, the OC : EC ratio was 0.49 ± 0.12, consistent with previous measurements of diesel-fuelled HDVs. Besides bulk carbonaceous aerosol measurement, polycyclic aromatic hydrocarbons (PAHs) were quantified. The sum of the PAHs concentration was 56 ± 5 ng m −3 and 45 ± 9 ng m −3 in the RA and JQ tunnel, respectively. In the JQ tunnel, benzo(a)pyrene (BaP) ranged from 0.9 to 6.7 ng m −3 (0.02-0. 1 ‰ of PM 2.5 ) whereas in the RA tunnel BaP ranged from 0.9 to 4.9 ng m −3 (0.004-0. 02 ‰ of PM 2.5 ), indicating an important relative contribution of LDVs emission to atmospheric BaP.Real-time measurements performed in both tunnels provided aerosol size distributions and optical properties. The average particle count yielded 73 000 cm −3 in the JQ tunnel and 366 000 cm −3 in the RA tunnel, with an average diameter of 48 nm in the former and 39 nm in the latter. Aerosol single scattering albedo, calculated from scattering and absorption observations in the JQ tunnel, indicates a value of 0.5 associated with LDVs. Such single scattering albedo is 20-50 % higher than observed in previous tunnel studies, possibly as a result of the large biofuel usage. Given the exceedingly high equivalent black carbon loadings in the RA tunnel, real time light absorption measurements were possible only in the JQ tunnel. Nevertheless, using EC measured from the filters, a single scattering albedo of 0.31 for the RA tunnel has been estimated. The results presented here characterise particulate matter emitted from nearly 1 million vehicles fuelled with a considerable amount of...

In the metropolitan area of São Paulo, Brazil, ozone and particulate matter (PM) are the air pollutants that pose the greatest threat to air quality, since the PM and the ozone precursors (nitrogen oxides and volatile organic compounds) are the main source of air pollution from vehicular emissions. Vehicular emissions can be measured inside road tunnels, and those measurements can provide information about emission factors of in-use vehicles. Emission factors are used to estimate vehicular emissions and are described as the amount of species emitted per vehicle distance driven or per volume of fuel consumed. This study presents emission factor data for fine particles, coarse particles, inhalable particulate matter and black carbon, as well as size distribution data for inhalable particulate matter, as measured in March and May of 2004, respectively, in the Jânio Quadros and Maria Maluf road tunnels, both located in São Paulo. The Jânio Quadros tunnel carries mainly light-duty vehicles, whereas the Maria Maluf tunnel carries light-duty and heavy-duty vehicles. In the Jânio Quadros tunnel, the estimated light-duty vehicle emission factors for the trace elements copper and bromine were 261 and 220 microg km(-1), respectively, and 16, 197, 127 and 92 mg km(-1), respectively, for black carbon, inhalable particulate matter, coarse particles and fine particles. The mean contribution of heavy-duty vehicles to the emissions of black carbon, inhalable particulate matter, coarse particles and fine particles was, respectively 29, 4, 6 and 6 times higher than that of light-duty vehicles. The inhalable particulate matter emission factor for heavy-duty vehicles was 1.2 times higher than that found during dynamometer testing. In general, the particle emissions in São Paulo tunnels are higher than those found in other cities of the world.

Burning of fuels from the transport sector is one of the main sources of air pollutants emission in urban areas. In order to implement public policies concerning air quality and public health, there is a need to develop emission inventories. Measurements inside traffic tunnels can provide an evaluation of emission factors of vehicles in-use in real conditions. In this paper, we show measurements of air pollutants for a mixed vehicle fleet, heavyand light-duty vehicles (HDVs and LDVs), in two tunnels in the metropolitan region of Sao Paulo in 2011 in order to calculate the pollutant emission factors (EFs). Measurements of carbon dioxide, carbon monoxide (CO), nitrogen oxides (NO x ) and particle matter (PM 2.5 ) were taken. High concentrations related to high-density traffic, especially during weekdays. EFs were heavily influenced by the pollutant species loads, so the total vehicle traffic and the fraction of HDV. The EF values for HDV were 3.6 and 9.2 g km -1 , for CO and NO x , respectively (5.8 and 0.3 g km -1 for LDV). To determine EF estimates, parameters such as velocity of the air, cross-sectional area and length of the tunnel and vehicles passing at 1-h time interval were considered.

Abstract. The objective of this work is to evaluate the impact of vehicular emissions on the formation of fine particles (PM2.5;  ≤  2.5 µm in diameter) in the Sao Paulo Metropolitan Area (SPMA) in Brazil, where ethanol is used intensively as a fuel in road vehicles. The Weather Research and Forecasting with Chemistry (WRF-Chem) model, which simulates feedbacks between meteorological variables and chemical species, is used as a photochemical modelling tool to describe the physico-chemical processes leading to the evolution of number and mass size distribution of particles through gas-to-particle conversion. A vehicular emission model based on statistical information of vehicular activity is applied to simulate vehicular emissions over the studied area. The simulation has been performed for a 1-month period (7 August–6 September 2012) to cover the availability of experimental data from the NUANCE-SPS (Narrowing the Uncertainties on Aerosol and Climate Changes in Sao Paulo State) project that aims to characterize emissions of atmospheric aerosols in the SPMA. The availability of experimental measurements of atmospheric aerosols and the application of the WRF-Chem model made it possible to represent some of the most important properties of fine particles in the SPMA such as the mass size distribution and chemical composition, besides allowing us to evaluate its formation potential through the gas-to-particle conversion processes. Results show that the emission of primary gases, mostly from vehicles, led to a production of secondary particles between 20 and 30 % in relation to the total mass concentration of PM2.5 in the downtown SPMA. Each of PM2.5 and primary natural aerosol (dust and sea salt) contributed with 40–50 % of the total PM10 (i.e. those  ≤  10 µm in diameter) concentration. Over 40 % of the formation of fine particles, by mass, was due to the emission of hydrocarbons, mainly aromatics. Furthermore, an increase in the number of small particles impaired the ultraviolet radiation and induced a decrease in ozone formation. The ground-level O3 concentration decreased by about 2 % when the aerosol-radiation feedback is taken into account.

Main TextA megacity typically refers to a metropolitan area with more than 10 million people. The number of megacities worldwide has increased from 8 in 1970 to 34 in 2016 with their total population exceeding 650 million (City Population, 2016). Air pollution, a consequence of increased population and urbanisation, is a common concern in megacities. Here we focus on the Metropolitan Area of São Paulo (MASP), which is the 5 th most populous urban region in the world and the second most populated region in Latin America (UN, 2014), making up ~10% of the total population of Brazil. With 21 million inhabitants and 8511 km 2 area (Fig. 1a), the MASP includes 38 metropolitan areas surrounding the city of São Paulo that has a population of 12 million (IBGE, 2016). What makes São Paulo distinctly different from all other megacities in the world is that its vehicle fleet operates exclusively on biofuel blends (sugarcane ethanol and soya diesel) in diesel, making it a unique biofuel-driven megacity. Yet, São Paulo's air quality face challenges to meet its national standards, which are relatively relaxed compared with the megacities of Asia (e.g., Delhi) or Europe (e.g., London). While the events of highly elevated concentrations of particulate matter (PM) are similarly common as in other megacities, the underlining factors responsible for them are unique to São Paulo and the questions are: (i) how can the air quality be improved considering that numerous interventions have already been taken in controlling emissions from vehicular fleet? (ii) how can the transportation system be transformed to make it emission-neutral? (iii) how the emissions from the main emitters such as the diesel trucks and buses can be reduced? and (iv) how the changes in the content of biofuel in diesel have influenced the exceedances and ozone formation? The aim of this paper is to propose answers to the above questions in the context of distinctness in the vehicle fleet, hitherto overlooked sources, underlining causes for pollution exceedances, and to suggest future directions and research needs to better understand and manage air quality of this unique megacity.Unique vehicle fleet and fuels it operates on: The MASP includes more than 7 million of road vehicles, with an average of 0.34 vehicles per inhabitant (CETESB, 2015). Light duty vehicles (LDVs), including private cars and taxis, dominate the traffic fleet with 85% share, followed by motorcycles (12%) and heavy duty vehicles (HDVs; 3%) (CETESB, 2013). The fleet of LDV, HDV and motorcycle have increased by 12.7, 10 and 9.6% between 2009 and 2012, respectively. The proportion of flexfuel vehicles that can run on ethanol or gasohol (gasoline with 25-27% ethanol) is increasing in MASP every day as 94% of vehicles sold in 2013 were flex-fuel (Posada and Façanha, 2015). Currently, the proportion of gasohol-driven LDVs is 55%, followed by flex-fuel vehicles (38%), ethanol (4%) and diesel (2%) (CETESB, 2012). To enable comparison, the relevant characteristics of the five world's largest megacitie...