Diurnal aging of biomass burning emissions: Impacts on secondary organic aerosol formation and oxidative potential

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Abstract. Residential biomass burning is an important wintertime source of aerosols. These particles are subjected to complex diurnal aging processes in the atmosphere, contributing to urban and regional air pollution. The cumulative impact of these aging cycles on aerosol composition and oxidative potential, a key toxicity metric, remains unclear. This study examined the oxidation cycles of biomass burning emissions during day-to-night and night-to-day transitions in the FORTH (Foundation for Research and Technology – Hellas) atmospheric simulation chamber, focusing on emissions from burning of olive wood. The final high-resolution AMS spectra of biomass burning organic aerosol (bbOA) after either oxidation cycle were almost identical (R² > 0.99, θ = 3°). This indicates transformation into similar biomass burning secondary organic aerosol (bbSOA) regardless of the initial step of the diurnal cycle. A 56 % average increase in the bbOA oxygen-to-carbon (O:C) ratio was observed during both cycle cases (from 0.38 ± 0.06 for the fresh to 0.59 ± 0.07 after aging). Additional OA mass was produced after the two cycles, varying from 35 to 90 % of the initial OA. The aging of the emissions led to a final water-soluble oxidative potential (WS-OP) increase of 60 % to 68 ± 18 pmol min-1 μg-1 for both cycles, but with notably different transient values that depend on the order of the oxidation regimes. The effect of each oxidation regime on the WS-OP of the bbOA depends on the airmass history. The evolution of the WS-OP was not well correlated with that of the O:C.

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