Oxidative aging of atmospheric organic aerosols (OA) substantially modifies their chemical compositions, physical properties, and hence the various environmental impacts. Here, we report observations of a previously unrecognized process leading to dimer formation during heterogeneous •OH-initiated oxidative aging of oxygenated OA. Isomer-resolved ion mobility mass spectrometry measurements and reaction-diffusion kinetic simulations are in good agreement, elucidating new mechanisms of dimerization by organic radical (i.e., peroxy and alkoxy radicals) cross reactions using glutaric acid as a surrogate oxygenated OA. These radical reactions are predicted to occur more prominently near the gas-particle interface following oxidation, especially in diffusion-limited viscous OA particles. Chemical structure analysis shows that esters dominate the detected dimers, followed by organic peroxides and ethers, highlighting the importance of acyl peroxy and acyloxy radicals. Simulations suggest that the reported dimer formation through the new interfacial mechanism could be appreciable under both laboratory and ambient conditions. Therefore, the dimers that are formed and enriched at the gas–particle interface are expected to play a crucial role in the effective reactivity, volatility, viscosity, and hygroscopicity of aged OA particles.

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Recent reports have linked severe lung injuries and deaths to the use of e-cigarettes and vaping products. Nevertheless, the causal relationship between exposure to vaping emissions and the observed health outcomes remains to be elucidated. Through chemical and toxicological characterization of vaping emission products, this study demonstrates that during vaping processes, changes in chemical composition of several commonly used vape juice diluents (also known as cutting agents) lead to the formation of toxic byproducts, including quinones, carbonyls, esters, and alkyl alcohols. The resulting vaping emission condensates cause inhibited cell proliferation and enhanced cytotoxicity in human airway epithelial cells. Notably, substantial formation of the duroquinone and durohydroquinone redox couple was observed in the vaping emissions from vitamin E acetate, which may be linked to acute oxidative stress and lung injuries reported by previous studies. These findings provide an improved molecular understanding and highlight the significant role of toxic byproducts in vapingassociated health effects.

Nitrogen-containing heterocyclic volatile organic compounds (VOCs) are important components of wildfire emissions that are readily reactive toward nitrate radicals (NO 3 ) during nighttime, but the oxidation mechanism and the potential formation of secondary organic aerosol (SOA) and brown carbon (BrC) are unclear. Here, NO 3 oxidation of three nitrogencontaining heterocyclic VOCs, pyrrole, 1-methylyrrole (1-MP), and 2-methylpyrrole (2-MP), was investigated in chamber experiments to determine the effect of precursor structures on SOA and BrC formation. The SOA chemical compositions and the optical properties were analyzed using a suite of online and offline instrumentation. Dinitro-and trinitro-products were found to be the dominant SOA constituents from pyrrole and 2-MP, but not observed from 1-MP. Furthermore, the SOA from 2-MP and pyrrole showed strong light absorption, while that from 1-MP were mostly scattering. From these results, we propose that NO 3initiated hydrogen abstraction from the 1-position in pyrrole and 2-MP followed by radical shift and NO 2 addition leads to lightabsorbing nitroaromatic products. In the absence of a 1-position hydrogen, NO 3 addition likely dominates the 1-MP chemistry. We also estimate that the total SOA mass and light absorption from pyrrole and 2-MP are comparable to those from phenolic VOCs and toluene in biomass burning, underscoring the importance of considering nighttime oxidation of pyrrole and methylpyrroles in air quality and climate models.

Atmospheric organic aerosols (OA) are complex mixtures of organic molecules that are usually highly functionalized through various oxidative processes. Understanding the volatilities and chemical compositions of OA is key to elucidating their environmental impacts. Thermal desorption coupling to mass spectrometry has been used as the main approach to examine both aspects of OA. In this work, we investigated the thermal desorption-induced chemical compositional change of OA from heterogeneous oxidation of glutaric acid and α-pinene ozonolysis. Using an ion mobility spectrometry mass spectrometer, coupled with total peroxide analysis and a mass transfer evaporation model, we determined diverse reactions in the particle phase during rapid heating under moderate desorption temperatures (less than 100 °C). These reactions include irreversible oligomer (e.g., esters and organic peroxides) decomposition into monomers and new oligomer formation from decarboxylation, CO elimination, decarbonylation, and dehydration. These chemical processes may effectively modify the volatility and chemical characteristics of the residual OA particles. Further, the monomeric products from thermal desorption could interfere with quantification of the original constituents without isomer separation. These findings could help reconcile the previously observed inconsistency of OA evaporation kinetics versus volatility distribution. Further, the results from this study could help interpret and constrain thermal desorption-based measurements of OA volatility and compositions.