Abstract
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.
Highlights
The Sao Paulo Metropolitan Area (SPMA), in the southeast region of Brazil, is considered a megalopolis comprised of Sao Paulo city and more than 38 municipalities
In order to study and understand the spatial and temporal variability of atmospheric aerosols, O3, and other pollutants (i.e. CO, nitrogen oxides (NOx)) during the study period, it was first necessary to analyse the behaviour of main meteorological systems acting on the atmospheric environment of the SPMA and surrounding areas
The Weather Research and Forecasting (WRF)-Chem community model has been used to evaluate the impact of vehicular emissions on the fine particles formation in the SPMA
Summary
The Sao Paulo Metropolitan Area (SPMA), in the southeast region of Brazil, is considered a megalopolis comprised of Sao Paulo city and more than 38 municipalities. One of the main concern in the SPMA is the occurrence of violations of air quality standards for ozone and fine particles at different air quality stations from the Sao Paulo Environmental. A. Vara-Vela et al.: Impact of vehicular emissions on the formation of fine particles. The air pollutant emissions in the SPMA are related to the burning of the following fuels: ethanol, gasohol (gasoline with 25 % ethanol), and diesel. Recent work of Carvalho et al (2015) reported a substantial increase in number of road vehicles from 1 million in 2000 to almost 7 million in 2014, together with an overview of the pollutants concentration, fuel use in the SPMA and the relationship between the emissions and the improvement in the air quality in past years
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