Effect of Photochemical Aging on Biomass Burning Emissions: Contributions of Oxidized Organic Nitrogen from a Variety of Biomass Types

Biomass burning is a major source of reactive organic nitrogen, yet the fuel-specific, combustion-dependent, and time-resolved chemistry of these emissions during photooxidation remains incompletely characterized. This study examines how stove emissions from four biomass fuels evolve under laboratory-controlled chamber oxidation, with a focus on the oxidized organic nitrogen (OON). Rather than sampling emissions over an entire burn, short-duration, burning-phase-resolved emissions were introduced into the Manchester aerosol chamber (MAC), allowing the chemical evolution of smoke from specific combustion phases to be examined in isolation. Wood (generated under flaming and smoldering conditions), peat, and leaves’ smoke were aged for 6 h, and the gas- and particle-phase composition was monitored using online and offline measurements. The results showed that gas-phase aging followed patterns consistent with fragmentation, leading to an increase in carbon oxidation state, a decrease in mean carbon number, and a reduction in aromaticity. In contrast, particle-phase aging showed an increasing contribution of larger, more aromatic and nitrogen-rich OON, consistent with the formation or retention of lower-volatility products through accretion-type processes, gas–particle partitioning, and/or heterogeneous oxidation. Clear burn-phase-, fuel-type-, and time-dependent evolution was observed, with organo-nitrate formation occurring predominantly within the first ∼2 h of photooxidation, followed by convergence in organic aerosol (OA) properties (f₄₃, f₄₄, f₆₀) with continued aging. Levoglucosan (f₆₀) decayed most rapidly in flaming wood emissions, reaching near-background levels by 6 h, which may contribute to the underestimation of aged BBOA in ambient-source apportionment studies. Overall, the results show that OON formation and evolution vary by fuel type, combustion phase, and oxidation time scale, with relevance for atmospheric modeling and exposure assessment.