A comparison of emissions from ethanol and petrol fuelled cars. Health risk assessment for Västra Götaland.
Facing the problems with global warming and the diminishing supplies of oil, alternative fuels are becoming more and more important for road traffic. One fuel that has been used for several years is ethanol (E85). The main discussion points regarding the environmental performance for ethanol as a fuel are related to the production. However, there are also some notable differences in the emissions between E85 and petrol fuelled vehicles. This relates to some extent to the emissions of nitrogen oxides (NOX) and particulate matter (PM) but mainly to the composition of the emitted organic compounds.These differences in emissions will potentially give different impacts on health and on the environment. This can be both through risks linked to the primary emissions and to secondary products formed in the atmosphere. In order to assess the health risks it is necessary to calculate the emissions in space and time, describe the dispersion and chemical reactions taking place in the atmosphere and to calculate the exposure to humans.In the present study two fuel scenarios for passenger cars are studied; one where the cars with Otto engines run on petrol and one where they run on E85. Two emission scenarios for 2020 are constructed and dispersion modelling is applied to obtain the human exposure to key pollutants. The dispersion modelling is performed with the EMEP model for extended Europe and the data obtained are used as boundary conditions for the model for the Västra Götaland Region. In the latter, detailed traffic and emissions scenarios are used together with the TAPM model to obtain concentration levels and population exposure. The differences in health impacts are then assessed.The differences in emission factors reflect in differences in emissions. The emission calculations for all Swedish road traffic show a decrease for the E85 scenario relative to the petrol scenario of 6.5% for NOX, 3.4% for PM2.5, 67% for benzene. For acetaldehyde there is an increase of 770%. The differences obtained from the TAPM modelling show decreased levels of NOX, ozone and benzene with E85 and increased levels of acetaldehyde. For the latter the increase may be up to 80%, while NOX and ozone show decreases of up to a few per cent and a few tenths of per cent, respectively. The health risk assessment shows decreased health risks in the E85 scenario relative the all-petrol scenario, due to the decreased NOX exposure, correlated with both preterm deaths and asthma. However, NOX may be mainly an indicator of unmeasured causal exhaust components in the epidemiological studies and thus the exposure-response functions for NOX may not be applicable in the present case where there is a difference in NOX exposure but not necessarily a difference in exposure to other exhaust components normally associated with NOX. Smaller effects are expected from the changes in ozone, acetaldehyde, PM2.5 and benzene exposure. The overall difference is about 1.6 preterm deaths per year for the Västra Götaland Region, with lower values for the E85 scenario, when the uncertain differences due to the differences in NOX exposure are not considered.