PM₁₀-bound polycyclic aromatic hydrocarbons: Concentrations, source characterization and estimating their risk in urban, suburban and rural areas in Kandy, Sri Lanka

Kandy, a world heritage city, is a rapidly urbanized area in Sri Lanka, with a high population density of ∼6000habkm⁻². As it is centrally located in a small valley of 26km² surrounded by high mountains, emissions from the daily flow of >100,000 vehicles, most are old and poorly maintained, get stagnant over the study area with an increased emphasis on the associated health impacts. Particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) are considered to be major pollutants in vehicular emissions; while PAHs account for the majority of mutagenic potency of PM. The purpose of the current study is to determine the 8h average concentrations of ambient PM₁₀ PAHs at twenty sites distributed in the urban, suburban and rural Kandy. Samples on glass micro fibre filters were collected with a high volume air sampler from July/2008 to March/2009, prepared through standard procedures and analyzed for PAHs by high performance liquid chromatography with ultraviolet visible detection. Further, the type and strength of possible anthropogenic emission sources that cause major perturbations to the atmosphere were assessed by traffic volume (24h) counts and firewood mass burnt/d at each sampling site, with the subsequent societal impact through quantitative cancer risk assessment. The results can serve as a base set to assess the PAH sources, pollution levels and human exposure. Mean total concentrations of 16 prioritized PAHs (∑PAHs) ranged from 57.43 to 1246.12ngm⁻³ with 695.94ngm⁻³ in urban heavy traffic locations (U/HT), 105.55ngm⁻³ in urban light traffic locations, 337.45ngm⁻³ in suburban heavy traffic stations, 154.36ngm⁻³ in suburban light traffic stations, 192.48ngm⁻³ in rural high firewood burning area and 100.31ngm⁻³ in rural low firewood burning area. The mean PM₁₀ concentration was 129μgm⁻³ (55–221μgm⁻³); which is beyond the WHO air quality standards. Polycyclic aromatic hydrocarbon signature and the spatial variation of ∑PAHs concentration with the type and strength of sources were applied to identify the sources of emission. A very similar and consistent source apportionment was obtained, which revealed that in the urban and suburban areas automobile emissions are the predominant daytime source of PAHs, but in suburbs with a low regression co-efficient between ∑PAHs and traffic volume indicating the impact of factors other than traffic volume. While domestic firewood burning is the major in rural areas, its commercial use has played a significant role in U/HT sites, with strong correlation to ∑PAHs. Current human exposure to PAHs can give rise to an increased cancer risk in Kandy in the coming decades, as denoted by the excess lifetime lung cancer risk of 3.31×10⁻³.