The Effects of Reducing Vehicular Emissions in Atmospheric Hydrocarbon Concentrations in Rio de Janeiro, Brazil.

Vehicles in urban environments are the main source of criteria pollutants as well as hydrocarbons (HC), which contribute to the formation of ozone and secondary organic aerosols (especially fine particles, PM2.5). In Brazil, HC emission standards have been set by the National Program for Controlling Air Pollution by Vehicles (PROCONVE) since 2007. The purpose of this study was to determine the concentration, speciation, and ozone forming potential (OFP) of C2-C12 HC, collected, in 2023, in an urban area of the city of Rio de Janeiro, that is characterized by vehicular emissions. Samples were collected by means of stainless-steel canisters, and then thermally desorbed and analyzed by heart-cutting multidimensional gas chromatography, with the aid of two detectors (MSD and FID) and two columns. The results were compared with data published in previous years, in the same seasonal period (the dry season) and at locations with similar emission features, to assess the effectiveness of the Brazilian vehicular emission control system. They show a reduction of total concentrations, in particular of aromatic compounds, and a lowering of the average OFP, despite an increase in the traffic volume. Clearly, the reduction in concentrations and atmospheric reactivity has resulted from attempts to ensure the vehicular fleet meets the requirements of PROCONVE.