Photochemical aging process on PM_2.5 bound PAHs emission from solid fuel combustion in traditional and improved stoves

Solid fuels are widely used as energy sources in the developing countries across the world. In this study, emissions of primary and secondary (i.e., photochemically aged) parent polycyclic aromatic hydrocarbons (p-PAHs) and their derivate from a variety of solid fuel burning were determined through a potential aerosol mass-oxidation flow reactor (PAM-OFR). The improved technology stoves showed reductions of 61.2–66.8% to the primary and secondary EFs of the total quantified PAHs (tPAHs) in comparison to the traditional stoves. In addition, the primary and secondary EFs of the tPAHs for the anthracite coal and maize straw charcoal were 80.9–88.7% and 19.4–51.6%, respectively, lower than those of the raw bituminous coal and maize straw briquette. Results demonstrated that the total p-PAHs and alkylated PAHs decreased for ~20% and ~ 50% after the 2- and 7- equivalent aged days, respectively, whereas the total oxygenated- and nitro-PAHs (i.e., o-PAHs and n-PAHs) had increases of ~30% and ~ 80%, respectively. Significant formations of carbonyl functional group in the aged samples were confirmed by the Fourier transform infrared spectroscopy, well consistent to the increases of EFs of the oxygenated species (e.g., o-PAHs). Unique diagnostic ratios for the o-PAHs and n-PAHs including 3 N-FLA/(3 N-FLA + 1 N-PYR) (> 0.2 for coal, < 0.2 for biomass) and 1,3DN-PYR/(1,3DN-PYR + 1,6DN-PYR) (>0.5 for coal; <0.5 for biomass) were discovered and firstly reported to differentiate the emissions from the solid fuels. Even though the aged total emission of benzo[a]pyrene equivalent factors decreased by 26.0–34.0%, the secondary atmospheric formations of more toxic derivatives of o-PAHs and n-PAHs are given to be a high concern. The findings of this study could assist in refining the speciated emission inventories and in evaluating the chronic and acute health risks. The results could also evidence that the advanced heating technology is an effective measure in the emission control of toxic organic substances.