Size distributions of polycyclic aromatic hydrocarbons in aerosol emissions from biofuel combustion

Size-resolved emission factors of polycyclic aromatic hydrocarbons (PAH), from biofuel combustion in cooking stoves in India, were measured using a dilution sampler providing sufficient dilution and quenching for aerosol stabilisation. Emission factors of PAH (total of ten compounds) from combustion of biofuels like wood, briquette and dung cake, respectively, ranged 2.0-3.2, 2.8-3.0 and 3.1-5.5 mg kg(-1) per mass fuel burnt and 1.9-3.3, 4.1-4.8 and 5.9-10.6 mg kWh(-1), per useful heat input. Dung cake and briquette fuels were significantly more polluting than wood. The PAH profiles showed a predominance of fluoranthene, pyrene and benz(a)anthracene from all biofuels. Ratios of the semi-volatile PAH (3-4 ring species) to the non-volatile PAH (5-ring and larger), were significantly higher from briquette and dung cake, than from wood combustion. The PAH size distributions from all stove-fuel systems were unimodal with mass median aerodynamic diameters (MMADs) in the 0.40-1.01 mum range, for both semi-volatile and non-volatile PAH. Average MMADs of the PAH size distributions from biofuel combustion were about 5-10 times larger than in emissions from fossil fuel combustion like from automobiles, with potential implications for lung deposition and health risk. The PAH/PM ratio showed no simple trend with average particle diameter, suggesting that PAH were associated with the aerosol through multiple mechanisms including adsorption and absorption. This hypothesis must be further examined through surface characterisation methods like PAH photoemission or through particle and PAH formation models for biofuel combustion systems. (C) 2002 Elsevier Science Ltd. All rights reserved.