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In urban environments, vehicle emissions are the main source of hydrocarbons (HC) which contribute to formation of tropospheric ozone. Since individual HC exhibit a wide range of ozone formation reactivity, speciated analyzes are necessary to assess the overall impact of vehicle exhaust emissions. Flex-fuel represents more than 90% of the light duty vehicle sales in Brazil. In this project, sampling and analytical methods were implemented and optimized for determination of speciated HC (C4-C12). Three flex-fuel vehicles (PROCONVE L4, L5 and L6) were tested, with both gasoline (E22) and ethanol (E100). Vehicle exhaust samples were obtained during emissions testing with FTP75 drive cycle (according to ABNT/NBR 6601) for each of the three phases: cold start, stabilized and hot start. The exhaust was collected in Tedlar bags and transferred to electropolished stainless steel canisters. HC were analyzed using thermal desorption and gas chromatography with a mass spectrometry detector. The analytical procedure was based on Method TO-15 (US EPA). Quantification was performed using a standard reference mixture that covered the entire concentration range of the samples. Using gasoline, E22, experimental emission values for phase 1 were 0.037, 0.017 and 0.019 g HC (C4-C12) km -1 for PROCONVE L4, L5 and L6 vehicles, respectively. Average MIR values (specific reactivity) for exhaust phase 1 were 3.04, 3.03 and 2.27, respectively, for PROCONVE L4, L5 and L6 vehicles. Weighted Maximum Incremental Reactivity (MIR) and Ozone Formation Potential (OFP) values, for C4-C12 fraction, were approximately in the intervals 2.00-2.76 and 0.013-0.099, respectively. Aromatic organic compounds in the exhaust of ethanol tests were < 1 ppmC for all phases and vehicles. Results suggest that these compounds are not due to the combustion of ethanol and their contribution for total HC (C4-C12) reactivity was considered negligible. A new method will be implemented in future tests to determine the low HC fraction (C2 and C3) by chromatography. Speciated HC emission data may be useful for technical discussions about the ozone formation potential using Brazilian fuels.

Speciated hydrocarbon analysis in exhaust emissions of flex fuel vehicles