The concentrations of 16 US-EPA criteria polycyclic aromatic hydrocarbons (PAHs) were monitored during different seasons at six different cities/ locations in the northern part of Belgium. Pressurized liquid extraction was used for the fast recovery of PAHs from quartz fibre filters (QFFs) and polyurethane foams (PUFs) in less than 30 minutes 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 ng/m 3 (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 2 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.

The levels of particulate polycyclic aromatic hydrocarbons (PAHs) were determined with a fast analytical approach to study their seasonal variations at Menen (Belgium) during 2003; they were found to be 5-7 times higher in January, February and December, in comparison to May, June and August. The annual average concentration of the sum of 16 US Environmental Protection Agency (EPA) criteria PAHs was 6.7 ng/m3 and around 63% of it was found to be probably carcinogenic to humans. The application of diagnostic ratio and principal component analysis showed vehicular emission as a major source. An increased ratio of 'combustion PAHs' to 'total EPA-PAHs' during the winter season indicated towards combustion activities. Further, the differences in PAHs concentration were assessed with relation to backward air mass trajectories, which show that the levels of PAHs increase when there is an air mass movement from Central and Western Europe and a fall when the trajectories spend most of their 4-day time over the Atlantic Ocean or in the Arctic region.

Public transport in Delhi was amended by the Supreme Court of India to use Compressed Natural Gas (CNG) instead of diesel or petrol. After the implementation of CNG since April 2001, Delhi has the highest fraction of CNG-run public vehicles in the world and most of them were introduced within 20 months. In the present study, the concentrations of various criteria air pollutants (SPM, PM(10), CO, SO(2) and NO(x)) and organic pollutants such as benzene, toluene, xylene (BTX) and polycyclic aromatic hydrocarbons (PAHs) were assessed before and after the implementation of CNG. A decreasing trend was found for PAHs, SO(2) and CO concentrations, while the NO(x) level was increased in comparison to those before the implementation of CNG. Further, SPM, PM(10), and BTX concentrations showed no significant change after the implementation of CNG. However, the BTX concentration demonstrated a clear relation with the benzene content of gasoline. In addition to the impact of the introduction of CNG the daily variation in PAHs levels was also studied and the PAHs concentrations were observed to be relatively high between 10 pm to 6 am, which gives a proof of a relation with the limited day entry and movement of heavy vehicles in Delhi.

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