Air emissions scenarios from ethanol as a gasoline oxygenate in Mexico City Metropolitan Area

The Mexican Biofuel Introduction Program states that during year 2010 the three biggest Mexican cities will have a gasoline blending with 6% ethanol available for all gasoline on-road vehicle fleet. Also in 2010 Mexican government has programmed to start the substitution of Tier 1 – the adopted US emission standards – by Tier 2, which are more stringent emission standards for motor vehicles and gasoline sulfur control requirements. How will the air emissions in the Mexico City Metropolitan Area (MCMA) be modified by using this blending? Four scenarios up to year 2030 were constructed and simulated using the Long-Range Energy Alternatives Planning model. Beginning with a BAU or reference scenario, in this scenario the current available fuel is a blending composed by 5% methyl tertiary butyl ether and 95% gasoline (MTBE5). Then, three alternative scenarios that use ethanol as an oxygenate are considered, one with the already programmed E6 blending (6% anhydride ethanol, 94% gasoline), for the sake of comparison the E10 blending (10% anhydride ethanol, 90% gasoline), and the other alternative to compare, ETBE13.7 (13.7% ethyl tertiary butyl ether, 86.3% gasoline; where ETBE is an ether composed by 48% anhydride ethanol and 52% isobutene). Emissions of carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), particulate matter (PM10), sulfur dioxide (SO2), total hydrocarbons (THC), benzene, formaldehyde, acetaldehyde and 1,3-butadiene were calculated using emission factors previously calculated using the adapted US-EPA computer model called MOBILE6-Mexico. Results show that Tier 1 and Tier 2 standards effectively lowers all emissions in all studied scenarios with the exception of PM10 and CO2 emissions. The alternative scenario E10 has the most total avoided emissions by weight but it is not the best when considering some individual pollutants. The greatest environmental benefit of ethanol in its final use as a gasoline oxygenate is for avoiding CO2 emissions.