Nitrogen oxides and ammonia in a traffic tunnel - determination of emission factors

Abstract

Since the diesel affaire became popular in 2015 vehicular exhaust emissions of nitrogen oxides have gained considerable attention. Especially emission factors for nitrogen oxides provided in the “Handbook Emission Factors for Road Transport” (HBEFA) are questioned. The aim of this master thesis was to determine real-world emission factors for nitrogen oxides for the Austrian vehicular fleet and to compare them with values given in HBEFA and other literature. In addition, emission factors for ammonia were determined. Ammonia is used in latest diesel exhaust after-treatment systems, i.e. the selective catalytic reduction via aqueous urea. Ammonia plays an important role in the formation of secondary particulate matter and has influence on ecosystems due to its nitrogen input. For the determination of vehicular emission factors, a measurement campaign in tunnel Kaisermühlen was conducted. Concentration measurements of nitrogen oxides and ammonia inside as well as outside the tunnel were performed. The longitudinal air velocity was measured directly in the tunnel with an impeller anemometer. Traffic data included number and velocity of passenger cars and heavy-duty vehicles (HDVs) and was provided by ASFINAG. Concentrations of nitrogen oxides inside the tunnel show a diurnal trend with maxima during rush hours, the longitudinal air velocity also correlates well with traffic density. Regarding ammonia, no relation between concentration and traffic number is observable. Calculated emission factors for nitrogen oxides agree well with data given in HBEFA. Therefore, the HBEFA adequately reflects real-world vehicular emissions for the entire Austrian vehicular fleet as well as for passenger cars and HDVs separately. Lower emission factors for ammonia were found compared to the HBEFA as well as other emission factors given in literature. It has to be mentioned that the vehicular fleet in other tunnel studies are mainly powered with gasoline, whereas in Austria diesel is the most fuel used. Thus, indicating lower ammonia emissions of diesel-driven vehicles. However, further investigations are needed for proving this assumption.