Online Measurements Reveal Contrasting Particle-Bound Reactive Oxygen Species and Chemical Composition in Emissions from Six Residential Solid Fuels

Abstract. Residential solid fuel combustion is an important source of atmospheric particulate matter (PM), yet source-dependent characteristics in particle-bound reactive oxygen species (ROS) and their chemical drivers remain poorly constrained. Here, we combined online ROS measurements using a Particle Into Nitroxide Quencher with high-resolution aerosol mass spectrometry to systematically characterize real-time emissions from six residential solid fuels under realistic residential burning conditions. Distinct fuel-dependent chemical signatures were identified: wood-based fuels showed high contributions from oxygen-containing organic ions (O/C = 0.61–0.63), whereas manufactured coals were dominated by hydrocarbon-rich fragments and stronger polycyclic aromatic hydrocarbon (PAH)-related signatures (5–7 % of OA). Importantly, these PAH-related ions were strongly associated with mass-normalized ROS (ROSm) across the six fuels (r2 = 0.98 for burn-averaged data), while weaker positive time-resolved correlations suggested additional influences from particle chemistry and combustion conditions. Consistently, manufactured coals exhibited substantially higher ROSm than wood-based fuels and peat (2.2–2.9 vs. 0.2–0.6 pmol BPEAnit-Me equivalents µg-1), together with greater within-burn variability. However, air-volume-normalized ROS (ROSv) revealed contrasting pathways to elevated ROS burden: coals exhibited the highest ROSv (140.1–305.4 pmol m-3) driven by their high intrinsic ROS activity, whereas peat reached similarly elevated levels (107.5 pmol m-3) primarily because of its high PM loading. Overall, by linking real-time particle-bound ROS with aerosol chemistry across six solid fuels, this study reveals distinct chemical and mass-loading contributions to ROS burdens, providing a basis for interpreting source-dependent oxidative characteristics of atmospheric combustion aerosols.