Seasonal and site-specific variation in vapour and aerosol phase PAHs over Flanders (Belgium) and their relation with anthropogenic activities

Abstract

The concentrations of 16 US-EPA criteria polycyclic aromatic hydrocarbons (PAHs) were monitored during various seasons at six different cities/locations in the northern part of Belgium. Pressurized liquid extraction (PLE) was used for the fast recovery of PAHs from quartz fibre filters (QFFs) and polyurethane foams (PUFs) in less than 30 min with minimum solvent consumption prior to their analysis with high-performance liquid chromatography. The concentrations of PAHs varied significantly at the studied sites and showed relation to different anthropogenic activities, such as vehicular emission (diesel/gasoline), incinerator, petroleum/oil burning, coke production, and wood/coal combustion. The annual average PAH concentration ranged from 17 (at a rural site) to 114 ng m⁻³ (near a petroleum harbour and industry). Most of the human carcinogenic PAHs were found to be associated with suspended particulate matter, which forms around ∼55% of the total PAH levels in aerosols. Relatively higher concentrations of PAHs were detected in aerosol samples during winter compared with other seasons, whereas no clear seasonal trend was observed for the vapour phase PAHs. This fraction is likely to be more local in origin; hence, it can be used as a site-specific characteristic. The site-specific concentrations of individual PAHs were also used in diagnostic ratio evaluations and in principal component analysis to find their relation with various anthropogenic activities. These results show that the vehicular emission is a major source of PAHs in Flanders, although other anthropogenic sources, as above, have also an impact on the total PAH levels.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are of major health concern, mainly due to their well-known carcinogenic and mutagenic properties (Ravindra et al., 2001). PAHs and their metabolites can form DNA adducts, which can induce mutation. These adverse properties, together with the still growing presence of PAHs in the environment, make their monitoring to be a top priority task in all programs for the evaluation of both the human health risk and the environmental hazards.

As it is known, PAHs are products of incomplete combustion and pyrolysis of fossil fuels and other organic materials from natural and anthropogenic sources. In urban and industrial atmospheres, PAHs are almost entirely of anthropogenic origin (Jones et al., 1989). PAHs are present in the atmosphere both in the vapour and the condensed (aerosol) phases (Bidleman et al., 1986). Low molecular weight PAHs tend to be more concentrated in the vapour phase, while the ones with higher molecular weight are often associated with particulates. Thus, it is important to reveal the abundance, distribution and potential sources of PAHs in the ambient air both in aerosols and in the vapour phase, so that air pollution caused by PAHs is to be efficiently controlled.

The main sources of PAHs in towns and cities are road traffic and certain industrial processes (Lee et al., 1995; Ravindra et al., 2001). In order to enhance the accuracy of emission source identification, principal component analysis (PCA) was used in many studies (Ho et al., 2002; Park et al., 2002; Fang et al., 2004; Dallarosa et al., 2005). Additionally, as the PAHs associated with suspended particulate matter (SPM) vary significantly as a function of their emission sources, some PAH concentration ratios have been used to indicate vehicular emission sources (Rogge et al., 1993; Venkataraman et al., 1994; Khalili et al., 1995). The amount and type of PAHs in urban and rural areas exhibit seasonal fluctuations with generally higher concentrations in the winter season (Cotham and Bidleman, 1995; Harrison et al., 1996; Ravindra et al., 2006).

In the present study the concentration of PAHs has been evaluated in Flanders, the northern part of Belgium, with the application of a fast analytical approach for their extraction. Samples were collected from the ambient air in both the vapour and particulate phases and the variation in PAH concentrations were assessed during different meteorological and seasonal conditions. A further purpose of the study was to identify the site-specific characteristics with relation to PAH concentrations and to apply PCA to find the possible emission sources of these compounds.