Studies of Polycyclic Aromatic Hydrocarbons in Urban Atmospheres

Abstract

Polycyclic aromatic hydrocarbons (PAH) are known to exist in urban atmospheres and are suspected of carcinogenic potential. The implementation of emission control regulations and changes in fuel usage over the last twenty-five years has affected air quality in general and PAH concentrations in particular. In addition, recent thermodynamic evidence suggests that previous determinations of PAH might be inaccurate. For these reasons, ambient concentrations of PAH have been investigated. The methodology involved in determining PAH has been re-examined within the context of a routine monitoring programme. Quantitative recovery of PAH from collected aerosols with their separation from the aliphatic component has been accomplished using a dimethyl sulphoxide extraction system. The concentrations of five representative PAH have been routinely determined at three environmentally dissimilar sites around Birmingham. The values found are less than 10 ng m-3 and show a marked seasonal variation. Multiple regression analysis between concentration and various meteorological parameters has been used to compare monitored and predicted concentrations of PAH. The internal residential concentrations of PAH appear to be essentially similar to external values. From the above data the background exposure of a Birmingham resident to benzo(a)pyrene was calculated and found to be approximately equivalent to the exposure of smoking one cigarette per day. Size distribution analysis indicates that PAH are predominantly associated with submicron particulate and are consequently capable of penetrating to human lungs as far as the alveoli. The recoveries of PAH from scot, when exposed to NOx, decrease with time at rates which correlate with molecular properties. Hence even in the absence of photolytic degradation a chemical route exists whereby the atmospheric PAH burden might be decreased.