Polycyclic aromatic hydrocarbons in size-segregated particulate matter from six urban sites in Europe
Introduction
Urban air thoracic particles (PM10; aerodynamic diameter Dp < 10 μm) form a highly complex mixture of different-sized solid and liquid particles originating from a large variety of anthropogenic and natural sources. Epidemiological studies have most often given stronger exposure–response relationships for mortality and morbidity outcomes in association with fine particles (PM2.5; Dp < 2.5 μm) than PM10. In addition, ultrafine (Dp < 0.1 μm) and coarse thoracic particle (PM2.5–10; 2.5 μm < Dp < 10 μm) concentrations have been independently associated with some health effects (World Health Organization (WHO), 2003, United States Environmental Protection Agency (USEPA), 2004). Ultrafine particles have been suggested to pose a great risk to human health due to their high number concentration in urban environments and potential to penetrate from the lung alveoli into the blood circulation (Delfino et al., 2005). However, there is increasing debate that particulate mass concentration may not be the most appropriate exposure parameter for the assessment of health risks of atmospheric pollution (Forsberg et al., 2005). For instance, many aromatic compounds, commonly identified in airborne particles, are suspected genotoxic agents and carcinogens, and some of them may also cause acute health effects (World Health Organization (WHO), 1998, European Commission (EC), 2001). Thus, inhalation of polycyclic aromatic hydrocarbons (PAHs) in particulate mixture is potentially a serious health risk.
The PAHs are products of incomplete combustion formed during burning or pyrolysis of organic matter such as coal, oil, biomass, gasoline and diesel (Finlayson-Pitts and Pitts, 2000, European Commission (EC), 2001). Besides being removed from the atmosphere by physical removal mechanisms (e.g. dry and wet deposition), the particulate PAHs disappear by going through gas–particle partitioning or by photodegradation (i.e. photolysis and/or photooxidation). There is a general agreement that photodegradation is the major chemical breakdown mechanism for 4- to 6-ring PAHs in the ambient aerosol (Finlayson-Pitts and Pitts, 2000). Gas–particle partitioning is also an important phenomenon for the loss of 2- to 4-ring particulate PAHs. Reaction rates, mechanisms and products of the overall phenomenon depend not only on oxidant levels, radiation intensity and the structure of specific PAHs but also on the physical and chemical surface properties of the particles, on/in which the PAHs are. However, the carcinogenic potential of particulate matter does not necessarily follow the decay of the known carcinogenic PAHs because the atmospheric oxidation of PAHs may result in the formation of aromatic polycyclic ketones and quinones that may be even more harmful to health than the original PAHs. This is likely especially when the particulate PAHs co-appear with transition metals in the atmosphere (Squadrito et al., 2001).
Benzo[a]pyrene (BaP) has been regarded as a marker of the total and carcinogenic PAHs (EC, 2001). The European Commission has set an annual target value of 1 ng m−3 for benzo[a]pyrene in ambient air. The atmospheric half-lives of the potent carcinogens range from 200 min for benzo[a]pyrene to >300 days for benzo[b]fluoranthene and >800 days for indeno[1,2,3-cd]pyrene. The half-lives have an inverse relationship with the reactivity of the compound (Finlayson-Pitts and Pitts, 2000). Thus, under certain conditions, e.g. summer season daytime with high oxidant levels, the benzo[a]pyrene concentration in ambient air can be expected to decline much faster than the benzo[b]fluoranthene and indeno[1,2,3-cd]pyrene concentrations. Therefore, the use of benzo[a]pyrene concentration alone as a representative indicator of carcinogenic PAH concentration in PM10 of polluted environments may lead to a false assessment.
The PAMCHAR project (www.pamchar.org) has been conducted to provide an in-depth chemical and toxicological characterisation of coarse, fine and ultrafine particulate samples collected during contrasting particulate pollution situations in six European cities. The previously published toxicological animal and cell studies of this project have shown major heterogeneities in the inflammatory and cytotoxic activities of fine and ultrafine particulate samples between the sampling campaigns (Happo et al., 2007, Jalava et al., 2007). The objectives of the present study were: i) to present the concentrations of 32 PAHs in ultrafine, fine and coarse particulate samples collected during six sampling campaigns across Europe, ii) to compare the contributions of known genotoxic and carcinogenic PAHs between the campaigns, iii) to assess the representativeness of benzo[a]pyrene as a universal marker of total and genotoxic PAHs in the present data set. Moreover, these data enabled a feasibility estimation of the ratios of certain PAHs to be used for identification of emission sources in different urban environments and climatic conditions. These results provide new insight into the distribution of PAHs between ultrafine, fine and coarse particle size ranges during different particulate pollution situations in Europe. To our best knowledge, the size-segregated PAH concentrations have not been published earlier from field campaigns in Duisburg, Prague, Amsterdam and Athens.
Section snippets
Sampling campaigns
A series of 7-week sampling campaigns were carried out in urban background sites of six European cities: Duisburg, Prague, Amsterdam, Helsinki, Barcelona and Athens. The campaigns were scheduled to include seasons of local public health interest due to high particulate concentrations or findings in previously conducted epidemiological studies. The sampling sites are characterised here briefly as “urban background”, which means that the sites are not directly exposed by traffic or other
Mass concentrations of polycyclic aromatic hydrocarbons
The PAH contents have been determined from the PM0.2, PM0.2–2.5 and PM2.5–10 samples of the six campaigns. The total PAH concentrations in these three size ranges, and in total PM10, are presented in Table 3 together with the mean particulate mass concentrations during the campaigns.
The values represent the average particulate mass and PAH concentrations of the whole 7-week campaign period. There was a maximum of 28-fold difference in PM2.5-PAH concentration between Prague winter and Athens
Conclusions
The results of this study showed differences, not only in total PAH concentrations but also in the concentrations of specific PAHs, between the six field campaigns in Europe. The PAH concentrations were lower in campaigns conducted during warm seasons than cold seasons. The lower PAH concentrations in the spring and summer campaigns of Barcelona, Helsinki and Athens, were likely influenced by higher degree of atmospheric photodegradation and evaporation during the sampling than in the three
Acknowledgements
This study was conducted within the framework of the project ‘Chemical and biological characterisation of ambient air coarse, fine, and ultrafine particles for human health risk assessment in Europe’ (PAMCHAR, http://www.pamchar.org/) co-ordinated by the National Public Health Institute of Finland. The financial support of the EC-FP5 Quality of Life and Management of Living Resources Programme (Contract QLK4-CT-2001-00423), the Academy of Finland (FINE-contracts 201701 and 201131), and the
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