Results obtained through combining different approaches, and aiming at contributing to the understanding of effects of bioethanol fuelled vehicles on urban air quality, are evaluated. The study is based on the results obtained by measurements, modelling and cost assessment estimates in a case study in Oslo under winter conditions, when the worst air quality episodes are registered and acetaldehyde and formaldehyde have the longest lifetime. Detailed levels of formaldehyde emitted by an E95-bus

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... nder on-road driving conditions are reported for the first time, and indicate that exposure to these levels may involve a high chance of developing cancer. Emission and air dispersion modelling were applied to evaluate the potential impact on urban environment. The results show that a full implementation of bioethanol (E85-vehicles) may affect urban air quality, subsequently affecting human health. Acetaldehyde emissions were estimated to increase by 233% for a full implementation of bioethanol (E85-vehicles) compared to the baseline (petrol/diesel vehicles), whereas CO 2 , NO x and exhaust particle emissions from traffic were estimated to decrease by 19%, 50% and 90%, respectively. Output from measurements and the air dispersion model were the basis for an impact assessment and economic valuation of implementing bioethanol fuel in a larger scale. The acetaldehyderelated health risk associated with emissions from bioethanol fuelled vehicles was estimated as oral cavity/pharynx cancer, and the related cost was found to increase by 300% for a full implementation of bioethanol relative to the current situation. Our study only shows part of the picture, and a full evaluation bearing in mind all potential pollutants' increases and reductions would be needed.