Background concentrations and source apportionment of polycyclic aromatic hydrocarbons in south-eastern Finland
Highlights
► PAHs in PM10 were collected at Virolahti, Finland. ► Benzo(a)pyrene was relatively high compared to other European background sites. ► PMF method was applied for daily PAH data combined with other pollutant data. ► Major source area of PAHs was in the eastern sector.
Introduction
Aerosols are known to have climate and health effects. Even though most aerosols (90%) are estimated to originate from natural sources (Kiehl and Rodhe, 1995), aerosols of anthropogenic origin are known to have adverse effects on human health, and they have also been associated with cardiovascular diseases, asthma and other respiratory diseases, and mortality (WHO, 2006). In Finland, the excess mortality caused by airborne particles is several hundred cases per year (Watkiss et al., 2005).
Polycyclic aromatic hydrocarbons (PAHs) are particularly harmful compounds in the anthropogenic aerosols due to their carcinogenic effect on humans. PAHs are formed during the incomplete combustion of organic material, and are emitted into the atmosphere from several natural and anthropogenic emission sources. These compounds can exist in both gas and particulate phases in the atmosphere. Lighter, highly volatile PAHs consisting of two or three aromatic rings exist in the gas phase, whereas heavier compounds with more aromatic rings are incorporated into particles in the atmosphere (Seinfeld and Pandis, 1998). Natural PAH sources include emissions from volcanic activity and forest fires, whereas anthropogenic sources consist of fossil fuel and biomass burning (Ravindra et al., 2008).
Wood combustion, especially in residential heating, is a significant PAH source in urban areas (Simoneit, 1984, Cotham and Bidleman, 1995) and especially in Northern Europe (Hellén et al., 2008, Hedberg et al., 2002, Glasius et al., 2008). Long-range transport also has a significant effect on the air quality of the Nordic countries (EMEP, 2008).
Diagnostic ratios and profiling of PAH concentrations as means to determine the source have been examined in several studies, e.g., De Raat and De Meijere (1991). Marchand et al. (2004) measured PAHs in French alpine valleys, and concluded that differences in PAH signatures between separate sources were small. However, Bari et al. (2009) found source fingerprints for softwood and hardwood burning, light oil burning, traffic, and road dust.
Due to the reactivity and long sampling times of PAH compounds, positive matrix factorization (PMF) or other source apportionment methods, which are commonly-used tools in air quality research (Dallarosa et al., 2005, Bari et al., 2009, Xie and Berkowitz, 2007, Shirivastava et al., 2007), are difficult to apply in the case of PAH data. Because of the different reaction rates, the relative concentration profiles of PAHs may change during transport (Sanderson et al., 2004, Galarneau, 2008).
This study was the first assessment of PAH pollution and its sources in south-eastern Finland, an area that is most influenced by the long-range transport of pollutants from southern and south-eastern pollution sources. PM10 samples for PAH analysis were collected at the Virolahti background station of the Finnish Meteorological Institute (FMI) in 2007–2008. Combining the PAH data set with that of other pollutants enabled the use of PMF for studying source apportionment at this background station. The data were analyzed with the EPA PMF 3.0 program. The conditional probability function (CPF) (Kim et al., 2003) was used to connect wind data and the factors from PMF in order to separate the different pollution sources and source areas. CPF provides the average wind direction (sector) for each factor.
Section snippets
Site and measurements
The Virolahti air quality station (60° 31′ 37″ N, 27° 40′ 33″ E, elevation 5 m above sea level) is located in south-eastern Finland, near the Russian border (Fig. 1), in a rural district on the coast of the Gulf of Finland and near the village of Virolahti. There is a wood-heated farmhouse at a distance of 80 m and in the direction of 140° from the measurement site. The nearest road is approximately 150 m to the north of the site. The traffic intensity on the road is low. The closest town,
Data analysis
Eight wind vectors per day were calculated using the Virolahti weather station data for wind direction and speed. Each vector was taken into account when calculating the daily average wind vector. These vectors were then classified into eight 45° sectors.
For selected daily samples, eight 120 h EMEP Flextra back-trajectories per day were calculated for a height of 500 m above ground level (Stohl et al., 1995, Stohl and Seibert, 1998).
The positive matrix factorization (PMF) method was used for
Weekly concentrations of PAHs
The weekly concentrations of the sum of the all analyzed PAH compounds (PAH sum) varied from 0.14 to 25.3 ng m−3, with the average being 3.27 ng m−3 (Table 3). For benzo(a)pyrene (B(a)P), the concentrations varied from 0.03 to 1.67 ng m−3 and the average was 0.23 ng m−3, which is well below the annual target value of 1 ng m−3 set by the European Union (2004/107/EC).
Average concentrations of PAHs in the PM10 fraction were highest in winter, while the PM10 mass displayed no such clear seasonal
Conclusions
At the Virolahti background station in south-eastern Finland between January 2007 and September 2008, the weekly PAH sum concentrations varied from 0.14 to 25.3 ng m−3, with an average of 3.27 ng m−3. For benzo(a)pyrene, the concentrations varied from 0.03 to 1.67 ng m−3 and the average was 0.23 ng m−3, which is well below the annual target value of 1 ng m−3 set by the European Union. The B(a)P concentration at Virolahti was reasonably high compared to the other European background sites.
Acknowledgements
The authors would like to thank Ms. Erja Ääpälä for taking care of the sampling at the Virolahti site. We also gratefully acknowledge the Tor and Maj Nessling foundation for financially supporting this project.
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