On the aliphatic and polyaromatic hydrocarbon levels in urban and background aerosols from belgium and the netherlands

Abstract

Concentrations of aliphatic hydrocarbons from eicosane up to tritriacontane, and of polycyclic aromatic hydrocarbons from anthracene and phenanthrene up to the dibenzanthracenes have been determined by GC-MS in ambient aerosol samples from seven different locations in Belgium, the Netherlands and Bolivia. Some of the sampling stations were situated in urban environments, others in residential suburban or rural sites. At one sampling station, the distribution of these hydrocarbons between the particulate and the gas phase was further investigated. The distribution patterns of aliphatic and polyaromatic hydrocarbons as a function of molecular weight or carbon number are reported for typical summer and winter samples collected under the most frequently occurring stable meteorological conditions, at two urban and one rural site in Belgium. Furthermore, hydrocarbon levels for two suburban stations are reported in terms of average concentrations over summer and winter periods as well as of frequency distributions. They are based on weekly samples collected over the whole year. The aliphatic hydrocarbon series shows a typical alternating pattern with higher concentrations for the compounds with odd carbon number in the range C 27–C 31. This effect is believed to result from natural emissions of biological origin (e.g. vegetation), whereas a more continuous distribution is observed for the anthropogenic emissions with a maximum around C 24–C 26. Gas phase contributions above C 24 to the total aliphatic hydrocarbon levels are not significant. The polyaromatic hydrocarbon series shows a constant distribution pattern with an expected increase in winter due to increased fossil fuel combustion processes, mainly of the higher molecular weight compounds, such as chrysene/benzanthracene, benzofluoranthenes and benzopyrenes. Among these, only chrysene/benzanthracene is also significant in the gas phase. At the background stations, the natural emission of higher odd aliphatic hydrocarbons is enhanced in summer samples as can be seen from the carbon preference index. For the background stations the combined interpretation of industrial activity data and prevailing wind direction data allows a reasonable understanding of the changes in pollution levels. However, this approach was not successful for the suburban samples of the survey studies, where changing meteorological factors such as variable winds, inversion conditions or rain simultaneously affected the organic composition of the aerosol.