Evolution of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) in fresh and aged biomass burning emissions

Polycyclic aromatic hydrocarbons (PAHs) and oxygenated polycyclic aromatic hydrocarbons (OPAHs) in the particulate phase of pellet stove and wood stove emissions were measured during a series of experiments at the FORTH Atmospheric Simulation Chamber Facility. Particle-phase polycyclic aromatic compounds (PACs) in emissions were characterized under fresh, daytime-aged (oxidation by OH radicals) and nighttime-aged (oxidation by NO₃ radicals) experimental conditions in the chamber to understand the role of each chemistry mechanism in shaping the PAH/OPAH profiles - under different conditions of humidity. Emissions of PAHs and OPAHs from a stove using pellet fuel were significantly lower, by factors of 4.6 and 3, respectively, compared to those from a conventional wood stove burning hardwood. Σ-OPAH levels were within the same order of magnitude as Σ-PAHs in both types of experiments. The PAHs emission factors of olive wood combustion were determined, and the Benzo(a)pyrene equivalent (BaP_eq) concentration, an indicator of its carcinogenicity, was 14 times higher for wood burning than pellet burning emissions, proving that just the replacement of the old technology heating appliances can reduce significantly population exposure to carcinogenic compounds. The chamber profile of non-volatile PACs produced from biomass burning presented similarities with the ambient biomass burning source profile determined from source apportionment analysis of ambient particle PACs in a Greek urban area. Oxidative ageing did not increase the concentrations of the measured PACs with the exception of 9,10-Anthraquinone, which was slightly enriched during nighttime and daytime ageing under low RH conditions. Increases in relative humidity (RH) accelerates PAC level reduction during ageing. The diagnostic ratios (DR) of PAH isomers, used for source identification, verified their pertinence for biomass burning emission characterization. Finally, Flt/(Flt + Pyr) increased and BaP/(BaP + BeP) decreased during ageing but tend to be robust even under the influence of ageing.