Screening-Level Emission Factors and Semi-Quantitative Toxic Equivalency of Polycyclic and Nitro-Polycyclic Aromatic Hydrocarbons from Residential Biomass Combustion in Chile

Abstract

Residential heater replacement programs in Chile have been evaluated primarily through fine particulate matter (PM) reduction metrics, without considering chemical speciation of the organic aerosols. This screening-level study characterized and compared particle-bound polycyclic aromatic hydrocarbon (PAH) and nitro-PAH emission factors from a residential firewood and a wood pellet heater, under controlled combustion conditions, and assessed their potential toxic equivalency (BaP-TEQ). Compound quantification used 1-nitropyrene as an index calibration compound; all results are semi-quantitative estimates with a combined analytical uncertainty of approximately 13–32%. Firewood combustion yielded a PAH-dominated emission profile with a total BaP-TEQ EF of 187.8 ng/kg, driven primarily by benzo[a]pyrene (BaP; individual contribution: 183.9 ng/kg). Wood pellet combustion showed a nitro-PAH-dominated profile under the applied semi-quantitative analytical conditions, with concentrations expressed as 1-nitropyrene-equivalent estimates and several compounds identified tentatively by NIST library matching, yielding a total screening-level BaP-TEQ EF of 972.1 ng/kg, approximately five-fold higher than firewood under the applied TEF framework and driven primarily by 6-nitrochrysene (toxic equivalency factor, TEF = 10). This screening-level estimate should not be interpreted as a direct human health risk between the two heating systems. Mean PM emission factors were 1.05 ± 0.55 g/kg for firewood combustion and 0.69 ± 0.15 g/kg for pellet combustion (approximately 1.5-fold difference). These results are reported descriptively given the screening-level nature of the analysis. The shift in particulate chemical profile from PAH-dominated in the firewood system to nitro-PAH-dominated in the pellet system suggests that wood pellets from pine may not be a sustainable approach to address air quality problems in Chile, since reductions in PM emissions alone may not capture relevant differences in the organic toxicological profile between these combustion systems. These findings provide a regional baseline for the chemical speciation of residential biomass emissions in Chile.