Emission factors for heavy metals from diesel and petrol used in European vehicles

Abstract

Heavy metals constitute an important group of persistent toxic pollutants occurring in ambient air and other media. One of the suspected sources of these metals in the atmosphere is combustion of transport fuels in road vehicles. However estimates of the emissions of these metals from road vehicles as reported in national emission inventories show a very high variability in emission factors used. This paper provides high quality data on concentrations of heavy metals in fuels and derives default emission factors from these. The paper discusses these values against the emission estimates presently reported by the Parties to the LRTAP Convention. The measured concentrations of heavy metals in petrol and diesel fuel show a high variability between different samples taken at gas stations throughout Europe. Metal concentrations in road transport fuels vary over two orders of magnitude, but all remain in the ppb region (a few tenths of a ppb to a few hundred ppb for all metals). The frequency distributions of the measurements could be approximated by lognormal distributions. We could not detect a significant difference between samples from different countries. The fuel based emission factors as derived in this study are compared with those related to lubricant use as published by Winther and Slentø (2010). For most HMs studied here, this would lead to an two to fourfold increase of the tailpipe emissions as derived from the fuel concentrations. The emission factors, including 95 percent confidence intervals were derived from a statistical analysis of the survey data. The proposed emission factors were generally lower than previously published emission factors. National emissions of heavy metals from vehicle exhaust, estimated in this study therefore are in many cases considerably lower than those reported by the countries for this source.