Evaluation of exposure factors applied in marginal external cost analysis of transportation related air pollution

This paper evaluates different air quality models for estimation of exposure factors and their implication for assessing the marginal external pollution costs of transportation using the impact pathway methodology. An element of the impact chain is the relation between changes in population exposure due to a change in emissions including a regional exposure factor and a local exposure factor. The focus is on Danish national air quality and human exposure models. Comparisons are made with similar calculations using the European Commission’s EcoSenseTransport model that is based on a simpler regional air quality exposures model that generates regional exposure factors that are higher than the Danish models. These differences may be explained by variations in geographical coverage, and by different estimations of absolute levels of exposures within the same area. Local exposure factors are derived for different city sizes as well as rural areas to differentiate the marginal external costs by degree of urbanisation. The Danish models produced lower marginal external costs than the EcoSenseTransport model.