Abstract

JAIMES-LOPEZ, J. Luis et al. Ranking tail-pipe vehicle emissions from reformulated gasolines by Electre method. Rev. Int. Contam. Ambient [online]. 2007, vol.23, n.2, pp.59-67. ISSN 0188-4999.

Even though gasoline reformulation has contributed in abating the high levels of some tropospheric pollutants in México City Metropolitan Area (MCMA), such as lead and sulfur dioxide, it is still being explored as practical alternative to alleviate other local air pollution problems, such as the high ozone levels. Because gasoline is a complex mixture of chemical compounds, the number of alternative reformulated gasoline fuels (RGF) to be tested is potentially very high. Thus, rapid and inexpensive methods are required to make such testing less costly. We report our experience while using a common ranking technique (Electre method) to select a subset of reformulated gasoline fuels (RGF) with low potential to form gaseous toxics and O₃-forming compounds in vehicle tail-pipe emissions, so that further studies might focus on the most promising of them. Ten RGF differing in contents of sulfur, aromatics, olefins and oxygenated compounds were subjected to chassis dynamometer tests in two vehicles representing different engine technologies: Tier 1, as representative of the currently dominant technology in MCMA, and Euro 4 which will soon enter the local market. Emissions sampling was done at constant volume (CVS) using the Urban Cycle driving test, a standardized Mexican chassis dynamometer test that simulates the slow driving conditions at MCMA. All comparisons were based on the contents of regulated gaseous pollutants (THC, CO, CO₂ and NO_x), CH₄ and VOC (HC and aldehydes and ketones) in the tail-pipe emissions. In tests with the local unleaded gasoline (n = 9), which was used as experimental reference (RF), the Tier 1 vehicle had significantly higher emissions of most measured pollutants than Euro 4. For selecting the fuels with lower emissions of toxics and O₃ forming compounds, the emission data were normalized (0-100) and weighed by two external factors (w1, for O₃ forming potential, and w2 for toxicity of each compound) and then subjected to Electre analysis. The best fuel options for data representing the average emissions from the two vehicle technologies were: F11 > F6 > F1 > F7 > F8 > F12, for w1; and F6 > F11 > F1> F5 > F8 > F12, for w2. Thus, by both weighing criteria, the Electre method selected F11, F6 and F1 as the best gasoline options. The ranks of the remaining fuels depended upon weighing. F11 was formulated with low concentrations of aromatics, olefins, benzene and sulfur, whereas F6 had the highest Reid vapor pressure (RVP) and 370 ppm sulfur. According to these results, the MCMA's air quality may be improved by substituting the currently used gasoline, which ranked as the last option, by another such as F11, F6 or F1.

Keywords : CVS tests; fuel reformulation; air quality; Electre method.