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1. Heterogeneous Oxidation of Atmospheric Organic Aerosol: Kinetics of Changes to the Amount and Oxidation State of Particle-Phase Organic Carbon

   https://doi.org/10.1021/acs.jpca.5b06946  

   Kroll, Jesse H. ; Lim, Christopher Y. ; Kessler, Sean H. ; Wilson, Kevin R. ( November 2015 , The Journal of Physical Chemistry A)
2. Kinetics and Products of Heterogeneous Hydroxyl Radical Oxidation of Isoprene Epoxydiol-Derived Secondary Organic Aerosol

   https://doi.org/10.1021/acsearthspacechem.3c00073  

   Yan, Jin ; Zhang, Yue ; Chen, Yuzhi ; Armstrong, N. Cazimir ; Buchenau, Nicolas A. ; Lei, Ziying ; Xiao, Yao ; Zhang, Zhenfa ; Lambe, Andrew T. ; Chan, Man Nin ; et al ( October 2023 , ACS Earth and Space Chemistry)

   Heterogeneous hydroxyl radical (•OH) oxidation is an important aging process for isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) that alters its chemical composition. It was recently demonstrated that heterogeneous •OH oxidation can age single-component particulate methyltetrol sulfates (MTSs), causing ∼55% of the SOA mass loss. However, our most recent study of freshly generated IEPOX-SOA particulate mixtures suggests that the lifetime of the complete IEPOX-SOA mixture against heterogeneous •OH oxidation can be prolonged through the fragmentation of higher-order oligomers. Published studies suggest that the heterogeneous •OH oxidation of IEPOX SOA could affect the organic atmospheric aerosol budget at varying rates, depending on aerosol chemical composition. However, heterogeneous •OH oxidation kinetics for the full IEPOX-SOA particulate mixture have not been reported. Here, we exposed freshly generated IEPOX-SOA particles to heterogeneous oxidation by •OH under humid conditions (relative humidity ∼57%) for 0−15 atmospheric-equivalent days of aging and derived an effective heterogeneous •OH rate coefficient (kOH) of 2.64 ± 0.4 × 10−13 cm^3 molecules−1 s−1. While ∼44% of particulate organic mass of nonoxidized IEPOX-SOA was consumed over the entire 15 day aging period, only <7% was consumed during the initial 10 aging days. By molecular-level chemical analysis, we determined oligomers were consumed at a faster rate (by a factor of 2−4) than monomers. Analysis of aerosol physicochemical properties shows that IEPOX-SOA has a core−shell morphology, and the shell becomes thinner with •OH oxidation. In summary, this study demonstrates that heterogeneous •OH oxidation of IEPOX-SOA particles is a dynamic process in which aerosol chemical composition and physicochemical properties play important roles. 

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3. Phase State and Relative Humidity Regulate the Heterogeneous Oxidation Kinetics and Pathways of Organic-Inorganic Mixed Aerosols

   https://doi.org/10.1021/acs.est.2c04670  

   Shen, Chuanyang ; Zhang, Wen ; Choczynski, Jack ; Davies, James F. ; Zhang, Haofei ( November 2022 , Environmental Science & Technology)
4. Effect of Aerosol Acidity on the Kinetics and Products of Heterogeneous Hydroxyl Radical Oxidation of Isoprene Epoxydiol-Derived Secondary Organic Aerosol

   YAN, JIN ; Armstrong, N. Cazimir ; Fankhauser, Alison ; Cooke, Madeline ; Buchenau, Nicolas A. ; Xiao, Yao ; Zhang, Zhenfa ; Lambe, Andrew ; Gold, Avram ; Ault, Andrew ; et al ( October 2022 , AAAR 40th Annual Conference)

   Abstract We recently demonstrated that the heterogeneous hydroxyl radical (·OH) oxidation is an important aging process for isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) that alters its chemical composition, and thus, aerosol physicochemical properties. Notably, dimeric species in IEPOX-SOA were found to heterogeneously react with ·OH at a much faster rate than monomers, suggesting that the initial oligomeric content of freshly-generated IEPOX-SOA particles may affect its subsequent atmospheric oxidation. Aerosol acidity could in principle influence this aging process by enhancing the formation of sulfated and non-sulfated oligomers in freshly-generated IEPOX-SOA. Many multifunctional organosulfate (OS) products derived from heterogeneous ·OH oxidation of sulfur-containing IEPOX-SOA have been observed in cloud water residues and ice nucleating particles and could affect the ability of aged IEPOX-SOA particles to act as cloud condensation nuclei. Hence, this study systematically investigated the effect of aerosol acidity on the kinetics and products resulting from heterogeneous ·OH oxidation of IEPOX-SOA particles. Gas-phase IEPOX was reacted with inorganic sulfate particles of varying pH (0.5 to 2.0) in an indoor smog chamber operated under dark, steady-state conditions to form freshly-generated IEPOX-SOA particles. These particles were then aged at a relative humidity of 60% in an oxidation flow reactor (OFR) for 0-15 days of equivalent atmospheric ·OH exposure. Aged IEPOX-SOA particles were sampled by an online aerosol chemical speciation monitor (ACSM) to measure real-time aerosol mass and chemical changes of the SOA particles, and were also collected onto Teflon filters and into PILS vials for molecular-level chemical analyses by hydrophilic liquid interaction chromatography method interfaced to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS), ion chromatography, and total OS mass amounts. 

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5. Effect of aerosol acidity on the kinetics and products of heterogeneous hydroxyl radical oxidation of isoprene epoxydiol-derived secondary organic aerosol

   Jin Yan, N. Cazimir ( March 2023 , Spring ACS Meeting 2023)

   We recently demonstrated that the heterogeneous hydroxyl radical (OH) oxidation is an important aging process for isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) that alters its chemical composition, and thus, aerosol physicochemical properties. Notably, dimeric species in IEPOX-SOA were found to heterogeneously react with OH at a much faster rate than monomers, suggesting that the initial oligomeric content of freshly-generated IEPOX-SOA particles may affect its subsequent atmospheric oxidation. Aerosol acidity could in principle influence this aging process by enhancing the formation of sulfated and non-sulfated oligomers in freshly-generated IEPOX-SOA. Many multifunctional organosulfate (OS) products derived from heterogeneous OH oxidation of sulfur-containing IEPOX-SOA have been observed in cloud water residues and ice nucleating particles and could affect the ability of aged IEPOX-SOA particles to act as cloud condensation nuclei. Hence, this study systematically investigated the effect of aerosol acidity on the kinetics and products resulting from heterogeneous OH oxidation of IEPOX-SOA particles. We reacted gas-phase IEPOX with inorganic sulfate particles of varying pH (0.5 to 2.5) in an indoor smog chamber operated under dark, steady-state conditions to form freshly-generated IEPOX-SOA particles. These particles were aged at a relative humidity of 65% in an oxidation flow reactor (OFR) for 0-21 days of equivalent atmospheric OH exposure. Through molecular-level chemical analyses by hydrophilic interaction liquid chromatography method interfaced to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS), we observed that highly acidic aerosol has higher oligomer ratio and exhibit much slower mass decay with OH oxidation (pH=0.5, lifetime = 56 days) as compared to less acidic aerosols (pH=2.5, lifetime=17 days). Based on atomic force microscopy (AFM) analysis, aerosol acidity could also affect the morphology and viscosity of IEPOX-SOA during OH oxidation process. 

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