Influence of metal-mediated aerosol-phase oxidation on secondary organic aerosol formation from the ozonolysis and OH-oxidation of α-pinene

Abstract

The organic component is the most abundant fraction of atmospheric submicron particles, while the formation mechanisms of secondary organic aerosol (SOA) are not fully understood. The effects of sulfate seed aerosols on SOA formation were investigated with a series of experiments carried out using a 9 m3 smog chamber. The presence of FeSO4 or Fe2(SO4)3 seed aerosols decreased SOA yields and increased oxidation levels in both ozonolysis and OH-oxidation of α-pinene compared to that in the presence of ZnSO4 or (NH4)2SO4. These findings were explained by metal-mediated aerosol-phase oxidation of organics: reactive radicals were generated on FeSO4 or Fe2(SO4)3 seed aerosols and reacted further with the organic mass. This effect would help to explain the high O/C ratios of organics in ambient particles that thus far cannot be reproduced in laboratory and model studies. In addition, the gap in the SOA yields between experiments with different seed aerosols was more significant in OH-oxidation experiments compared to ozonolysis experiments, while the gap in estimated O/C ratios was less obvious. This may have resulted from the different chemical compositions and oxidation levels of the SOA generated in the two systems, which affect the branching ratio of functionalization and fragmentation during aerosol oxidation.

Chemical and cellular oxidant production induced by naphthalene secondary organic aerosol (SOA): effect of redox-active metals and photochemical aging

“…The degree of oxidation is a parameter of interest for organic aerosol, as atmospheric photochemical aging occurs over an aerosol’s lifetime, yielding more oxidized species and aerosol with a higher 65 . The observed difference in ROS/RNS levels between AS and FS seeded SOA is likely an effect of the degree of oxidation, where the presence of iron serves to increase the oxidation of species via Fenton-like reactions (Table S1 ) 51 , 52 . In fact, a positive exponentially decreasing trend was observed between ROS/RNS levels and of aerosol for all experiments (Fig.…”

Enhancement of secondary organic aerosol formation and its oxidation state by SO<sub>2</sub> during photooxidation of 2-methoxyphenol

“…After gas species and seed particles in the chamber were mixed well, the photooxidation experiment was carried out with the fan turned off. In this work, the OH concentrations in the chamber were (1.3-2.2) × 10 6 molecules cm −3 , calculated based on the degradation rate (7.53×10 −11 cm 3 molecule −1 s −1 ) of guaiacol with OH radicals (Coeur-Tourneur et al, 2010a). The chemicals and gas samples used in this work were described in Supplement.…”

“…Its emission factor of wood burning is in the range of 172-279 mg kg −1 wood . In recent years, the reactivity of gas-phase guaiacol toward OH radicals (Coeur-Tourneur et al, 2010a), NO 3 radicals (Lauraguais et al, 2016;Yang et al, 2016), Cl atoms (Lauraguais et al, 2014a), and O 3 (El Zein et al, 2015) has been investigated, suggesting that its degradation by OH and NO 3 radicals might be predominant in the atmosphere. Meanwhile, several studies have reported the significant secondary organic aerosol (SOA) formation from guaiacol oxidation by OH radicals, produced from the photolysis of the OH precursors (i.e., H 2 O 2 and CH 3 ONO) (Ahmad et al, 2017;Lauraguais et al, 2014b;Yee et al, 2013).…”

Enhancement of Secondary Organic Aerosol Formation and its Oxidation State by SO<sub>2</sub> during Photooxidation of 2-Methoxyphenol

“…Although many studies concentrated on the SOA production from the oxidation of volatile organic compounds (VOCs), the reported SOA yields showed high variability for a given precursor (Chu et al, 2016(Chu et al, , 2017Ge et al, 2017a;Lauraguais et al, 2012Lauraguais et al, , 2014bNg et al, 2007;Sarrafzadeh et al, 2016;Yee et al, 2013). This variability is mainly dependent on the numerous factors, e.g., pre-existing seed particles, SO2 level, NOx level, humidity, and temperature.…”

“…This variability is mainly dependent on the numerous factors, e.g., pre-existing seed particles, SO2 level, NOx level, humidity, and temperature. Two of the critical factors are the impacts of preexisting seed particles and SO2 level on SOA formation (Chu et al, 2016(Chu et al, , 2017Ge et al, 2017a). In addition, the atmospheric concentration of SO2 could be up to close 200 ppb in the severely polluted atmosphere in China, and SOA from biomass burning and sulfate formation could significantly contribute to severe haze pollution (Li et al, 2017).…”