C ]C non-methane hydrocarbon measurements in 5 8 Copenhagen: concentrations, sources and emission estimates

Hourly measurements of 23 non-methane hydrocarbons NMHC. ranging from C5 to C8 were measured in the busy street Jagtvej in central Copenhagen during 5 working days in December 1997. The compounds were concentrated at absorbent tubes by active sampling and subsequently analyzed by thermal desorption and gas chromatography. Parallel measurements of benzene and toluene using a different technique were performed to validate the results. Good agreement were observed r)0.97.. The aromatic compounds were the most abundant species with average concentrations ranging between 10.2 ppbv for toluene to 2.0 ppbv for ethylbenzene. Average benzene concentrations were 3.4 ppbv. The concentrations of alkanes were 0.2]2.4 ppbv and of the alkenes 0.03]0.4 ppbv. All components were highly correlated with primary emitted CO r)0.88. and benzene r)0.89. which identifies petrol fueled motor vehicles as the major source. The emission factors of the hydrocarbons from petrol fueled vehicles were calculated on the basis of the emission factor known for benzene 0.11 g kmy1.. Highest emission factors were observed for the aromatic compounds up to 0.41 g kmy1 for toluene., which is in accordance with the literature. The NMHC content of petrol fuel was also measured by GC-MS analysis. An enhancement of benzene and isoprene were observed relative to o-xylene when comparing the found emission factors with the NMHC composition of the petrol fuel. The generation of benzene during combustion and evaporative emissions of isoprene are possible explanations for this observation.