Traffic related air pollution with emphasis on particle associated polycyclic aromatic hydrocarbons : Tire wear and biodiesel exhaust emissions

Sammanfattning: Particulate matter (PM) is regarded as one of the more important components of air pollution causing adverse health effects. A large group of compounds associated with PM are polycyclic aromatic compounds (PACs) which comprises polycyclic aromatic hydrocarbons (PAHs). Several PACs are known for their mutagenic and carcinogenic properties as well as have the ability to induce oxidative stress.With the growing importance of non-exhaust particles relative to vehicular tail-pipe emissions in urban air, it is necessary to investigate the possible contribution of PAHs from the different non-exhaust sources, as these inputs are far less characterized than tail-pipe emissions and their impact on human health is largely unknown.In this thesis automobile tires, an important non-exhaust traffic related source to particles, have been investigated for its content of highly carcinogenic dibenzopyrene isomers. In a separate study benzothiazoles, a class of compounds used as vulcanization accelerators in tire manufacture, were determined to evaluate their use as potential markers for tire wear particles in ambient air.Analysis of the tires showed a substantial variation in the PAH content between different makes of tires, likewise did the benzothiazoles content vary. By determining benzothiazole in air particles collected at a busy street in Stockholm the tire rubber contribution to airborne particles was estimated to 0.7 and 5.5 % for PM10 and all airborne particles, respectively. Together with the determined content of dibenzopyrenes and the relatively low mass contribution of tire wear to airborne particles in the urban air, estimated in this thesis as well as suggested by the literature, tire wear appears to be a minor traffic related contributor of these PAH compounds in the urban air. Nevertheless, tire wear may be an important source to 2-mercaptobenzothiazole in the urban air.Biodiesel, a biofuel produced from plant and animal fats, has been suggested as a suitable replacement for conventional petroleum based diesel fuels. While the majority of studies have focused on health outcomes from petroleum diesel exhaust exposure, human health effects related to biodiesel exhaust exposure is much less investigated.Biodiesel exhaust particles have been compared with conventional petroleum diesel by determining >40 PAHs in two separate studies on two different diesel engines, running on neat rapeseed methyl ester (RME), petroleum diesel and a fuel blend of 3:7 RME : petroleum diesel. One of the biodiesel studies also included determination of four oxygenated PAHs (Oxy-PAHs).The exhaust from biodiesel combustion differed from petroleum diesel combustion with regards to particle size, number of emitted particles, relative amount of volatile material adsorbed on the particles and emission of particle-associated PAHs and Oxy-PAHs. A portion of these volatile compounds originated from unburned or partially combusted biodiesel fuel, which interfered with the analysis. A sample cleanup method was therefore developed for determination of PAH in lipid rich matrices. Biodiesel combustion produced lower emission of PAHs and Oxy-PAH with the exception of a few PAHs with higher molecular weights. In comparison with petroleum diesel, the biodiesel particles had a higher relative composition of PAHs with more than four rings.