Contribution of Fossil Fuels and Wood Combustion to Carcinogenic PAHs in the Ambient Atmosphere of a Tropical Megacity

Weekly particulate matter sampling was carried out at a peri-urban site located in megacity Delhi, India for 1 year (2009-2010) and the annual mean PM10 level was found to be ∼9 times the World Health Organization limit. Seasonal variation of PAHs (range 37.2-74.0 ng m-3) was significant with winter values being 72% and 68% higher than summer and monsoon respectively. Principal component analysis coupled with multiple linear regression identified diesel, natural gas and lubricating oil combustion (49.5%), wood combustion (25.4%), gasoline (15.5%) and coal combustion (9.6%) sources for the observed PAHs. Heavy traffic on the national highway and arterial roads and domestic emissions from suburban households in the vicinity of the site appeared to have significantly affected its air quality. A substantial portion (∼55%) of the aerosol PAH load was comprised of carcinogenic species, which yielded a considerably high lifetime inhalation cancer risk estimate (8.7E-04). If considered as a conservative lower-bound estimate, this risk translates into ∼211 excess cancer cases for lifetime inhalation exposure to the observed PAH concentrations in Delhi.