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Abstract Burning plastic waste releases massive amounts of atmospheric particulate matter (PM), but its chemical composition and health-related properties are largely unelucidated. Here we characterize chemical composition of PM generated from burning common types of plastics and quantify reactive oxygen/chlorine species and PM oxidative potential (OP). We find that plastic burning PM contains high levels of environmentally persistent free radicals (EPFRs), transition metals, and polycyclic aromatic hydrocarbons. In the aqueous phase, PM generates hydrogen peroxide, •OH radicals, and carbon-centered organic radicals, exhibiting high levels of OP as characterized by dithiothreitol (DTT) and OH assays. Remarkably, plastic burning PM is associated with high concentrations of hypochlorous acid. Kinetic model simulations demonstrate that the PM respiratory deposition leads to •OH formation via complex redox reactions among its constituents and antioxidants in lung lining fluid. Our study highlights significant atmospheric and health implications for unregulated plastic burning, particularly common in many areas of developing countries. 

The high levels of sulfate in wintertime particles in Fairbanks, Alaska, are a subject of keen research interest and regulatory concern. Recent results from the 2022 Alaska Layered Pollution And Chemical Analysis (ALPACA) field campaign indicate that roughly 40 % of wintertime sulfate in Fairbanks is secondary, with hydrogen peroxide (HOOH) the dominant oxidant. Since formation of HOOH in the gas phase should be negligible during ALPACA because of high levels of NOx, we examined whether reactions within particles could be a significant source of HOOH. To test this, we collected particulate matter (PM) samples during the ALPACA campaign, extracted them, illuminated them with simulated sunlight, and measured HOOH production. Aqueous extracts showed significant light absorption, a result of brown carbon (BrC) from sources such as residential wood combustion. Photoformation rates of HOOH in the PM extracts (PMEs; normalized to Fairbanks winter sunlight) range from 6 to 71 µM/h. While light absorption is nearly independent of pH, HOOH formation rates decrease with increasing pH. Extrapolating to the concentrated conditions of aerosol liquid water (ALW) gives an average rate of in-particle HOOH formation of ∼ 0.1 M/h. Corresponding rates of sulfate formation from particle-produced HOOH are 0.05–0.5 µg/m3/h, accounting for a significant portion of the secondary sulfate production rate. Our results show that HOOH formed in particles makes an important contribution to sulfate formation in ambient wintertime particles, even under the low actinic flux conditions typical of winter in subarctic locations like Fairbanks. 

Abstract. Subarctic cities notoriously experience severe winter pollution episodes with fine particle (PM2.5) concentrations above 35 µg m−3, the US Environmental Protection Agency (EPA) 24 h standard. While winter sources of primary particles in Fairbanks, Alaska, have been studied, the chemistry driving secondary particle formation is elusive. Biomass burning is a major source of wintertime primary particles, making the PM2.5 rich in light-absorbing brown carbon (BrC). When BrC absorbs sunlight, it produces photooxidants – reactive species potentially important for secondary sulfate and secondary organic aerosol formation – yet photooxidant measurements in high-latitude PM2.5 remain scarce. During the winter of 2022 Alaskan Layered Pollution And Chemical Analysis (ALPACA) field campaign in Fairbanks, we collected PM filters, extracted the filters into water, and exposed the extracts to simulated sunlight to characterize the production of three photooxidants: oxidizing triplet excited states of BrC, singlet molecular oxygen, and hydroxyl radical. Next, we used our measurements to model photooxidant production in highly concentrated aerosol liquid water. While conventional wisdom indicates photochemistry is limited during high-latitude winters, we find that BrC photochemistry is significant: we predict high triplet and singlet oxygen daytime particle concentrations up to 2×10-12 and 3×10-11 M, respectively, with moderate hydroxyl radical concentrations up to 5×10-15 M. Although our modeling predicts that triplets account for 0.4 %–10 % of daytime secondary sulfate formation, particle photochemistry cumulatively dominates, generating 76 % of daytime secondary sulfate formation, largely due to in-particle hydrogen peroxide, which contributes 25 %–54 %. Finally, we estimate triplet production rates year-round, revealing the highest rates in late winter when Fairbanks experiences severe pollution and in summer when wildfires generate BrC. 

Wildfires, which have been occurring increasingly in the era of climate change, emit massive amounts of particulate matter (PM) into the atmosphere, strongly affecting air quality and public health. Biomass burning aerosols may contain environmentally persistent free radicals (EPFRs, such as semiquinone radicals) and redox-active compounds that can generate reactive oxygen species (ROS, including ·OH, superoxide and organic radicals) in the aqueous phase. However, there is a lack of data on EPFRs and ROS associated with size-segregated wildfire PM, which limits our understanding of their climate and health impacts. We collected size-segregated ambient PM in Southern California during two wildfire events to measure EPFRs and ROS using electron paramagnetic resonance spectroscopy. EPFRs are likely associated with soot particles as they are predominantly observed in submicron particles (PM 1 , aerodynamic diameter ≤ 1 μm). Upon extraction in water, wildfire PM mainly generates ·OH (28–49%) and carbon-centered radicals (∼50%) with minor contributions from superoxide and oxygen-centered organic radicals (2–15%). Oxidative potential measured with the dithiothreitol assay (OP-DTT) is found to be high in wildfire PM 1 , exhibiting little correlation with the radical forms of ROS ( r 2 ≤ 0.02). These results are in stark contrast with PM collected at highway and urban sites, which generates predominantly ·OH (84–88%) that correlates well with OP-DTT ( r 2 ∼ 0.6). We also found that PM generated by flaming combustion generates more radicals with higher OP-DTT compared to those by smoldering or pyrolysis.