Determinação de hidrocarbonetos (C4-C12) no escapamento de veículos flex

Abstract

In order to control vehicle emission, the Environment National Council (CONAMA) created the Air Pollution Control Program for Motor Vehicles (PROCONVE), establishing the first emission limits for some of the main air pollutants for light-duty vehicles. Among these pollutants, hydrocarbons (HC) stand out, mainly for their ability to form tropospheric ozone in photo-oxidation reactions. This work aimed to develop a methodology for the determination of HC in exhaust emissions from flexible-fuel vehicles in Brazil, which represent more than 90% of light-duty vehicles fleet, using well-established methods such as TO-15, developed by the United States Environmental Protection Agency (US EPA). The HC sampling was performed with standardized vehicle tests using reference fuels (gasoline, E22, and hydrated ethanol, E100) and involved three vehicles (PROCONVE L4, L5 and L6). The samples were collected in electropolished stainless steel canisters during the three phases of the procedure according to ABNT NBR 6601. The analysis was carried out using a thermal desorption-gas chromatography-mass spectrometry system. Quantification was executed using a standard reference HC mixture. Using gasoline, E22, the average weighted emission values were 38.69, 19.32 and 5.57 mg km-1 for PROCONVE L4, L5 and L6 vehicles, respectively. The values of ozone-forming potential (OFP) were found in the range of 8.81 141.49 mg km-1, while the weighted values of specific MIR were in the range of 2.58 3.35. For the tests with hydrated ethanol, E100, the presence of HC in the C4-C12 range was reported, among them aromatic HC. However, the fraction corresponding to these compounds was insignificant (at most 2.6%) and their contribution to the values of specific MIR and OFP is negligible, making it impossible to obtain representative values. The data obtained in the speciation of HC can be used in further technical discussions involving tropospheric ozone formation processes.