Volatile Hydrocarbons in Ambient Air. Gas Chromatographic Assessment, Emissions and Human Exposure
Hydrocarbons in ambient air constitute a potential health risk for a large number of individuals. The work reported in this thesis focusses on human exposure to volatile hydrocarbons in ambient air. The analytical determinations were made by adsorbent sampling followed by thermal desorption and gas chromatography. The concentrations of about 40 specific volatile alkanes, alkenes, alkadienes, alkynes and arenes from various sources were determined.
The observed hydrocarbon composition with large proportions of alkanes and alkylbenzenes in urban air demonstrates that human exposure in urban areas is caused predominantly by petrol-fuelled cars. Biomass combustion gives rise mainly to unsaturated hydrocarbons. Increasing combustion efficiency causes decreasing emissions but increasing proportions of benzene, ethene and ethyne. Tobacco smoke is characterized by high proportions of isoprene and 1,3-butadiene.
In two short urban road tunnels (500-700 m), the hydrocarbon concentrations were several times higher than in streets with similar traffic. It is concluded that long road tunnels with large numbers of vehicles must be questioned with regard to health hazards.
Observed concentrations of hydrocarbons indicate that typical ratios between roof level, street-side, and car coupés are 1 : 5 : 10. Passenger exposure to traffic emitted volatile hydrocarbons is 2-3 times higher for diesel bus commuters than for train commuters. From these comparisons, it is evident that people's activities, in terms of their time spent close to traffic sources, will strongly influence their hydrocarbon exposure dose.
A comparison of urban air monitoring of benzene, toluene and p-xylene by the gas chromatographic technique used in this work and by differential optical absorption spectroscopy (DOAS) demonstrated that DOAS measurements were unreliable at the concentration levels prevailing in a city like Göteborg.