Chemistry of hydroperoxycarbonyls in secondary organic aerosol

Abstract

Highly oxidized multifunctional compounds (HOMs) formed through gas-phase reactions are thought to account for a significant fraction of the secondary organic aerosol (SOA) formed in low-nitric oxide (NO) environments. HOMs are known to be peroxide-rich and unstable in SOA, however, and their fate once they partition into particles is not well understood. In the study reported here, we identified particle-phase reactions and decomposition products for an a-alkoxy hydroperoxyaldehyde that served as a convenient model for HOMs, and also quantified rate and equilibrium constants for cyclic peroxyhemiacetal formation and the effects of particle acidity and relative humidity on reaction products and timescales for decomposition of peroxide-containing compounds. Sulfuric acid increased the rate of acetal formation and subsequent peroxide decomposition, but the effect was eliminated when aqueous seed particles were used in humid air, indicating that organic/aqueous phase separation can affect the ability of strong acids to catalyze these and other reactions in SOA. The results will be useful for understanding and predicting the atmospheric fate of organic peroxides and the effects of their particle-phase reactions on SOA composition. ARTICLE HISTORY

Online Characterization of Organic Aerosol by Condensational Growth into Aqueous Droplets Coupled with Droplet-Assisted Ionization

“…Oxygen numbers of the products are generally lower than the original HOMs owing to, e.g., equations 1 and 2 of Scheme . We suggest that these processes, which could in principle occur in either the gas or particle phase, contribute to the difference between the particle phase product distribution in Figure and reported gas-phase distributions of HOMs. − When viewed from the perspective of particle-phase chemistry, the mass spectrum in Figure provides evidence for substantial intermolecular reactivity within the particle phase, producing an interconnected oligomeric system. This reactivity may provide a molecular explanation for the high viscosity of the particle phase.…”

Compositional Evolution of Secondary Organic Aerosol as Temperature and Relative Humidity Cycle in Atmospherically Relevant Ranges

“…22−28 Some of the decomposition is induced by heat, 22,23,25,26 while some occurs at room temperature on the time scale of hours. 27,28 These evidence suggest that certain oligomers in SOA are thermally unstable and might decompose or react under atmospheric temperature ranges, provided sufficient time. Simultaneously, particle-phase accretion reactions also take place, in which RH may play crucial roles.…”

“…One prior study has shown that as the temperature cycles between atmospherically relevant set points, the SOA mass could not be reproduced, suggesting insufficient condensation/evaporation, or irreversible particle-phase reactions, or both . Growing evidence has demonstrated that atmospheric SOA could exist in distinct phase state and viscosity governed by RH, − and do not always reach equilibrium upon evaporation and condensation. − Further, common SOA constituents such as organic peroxides and some other types of oligomers were found to be labile and could decompose. − Some of the decomposition is induced by heat, ,,, while some occurs at room temperature on the time scale of hours. , These evidence suggest that certain oligomers in SOA are thermally unstable and might decompose or react under atmospheric temperature ranges, provided sufficient time. Simultaneously, particle-phase accretion reactions also take place, in which RH may play crucial roles. − It is thus imperative to determine how SOA chemical compositions transform, as the bulk and on the molecular level, under temperature and RH changes representative of the real atmosphere.…”

A Near-Explicit Mechanistic Evaluation of Isoprene Photochemical Secondary Organic Aerosol Formation and Evolution: Simulations of Multiple Chamber Experiments with and without Added NOx

“…Tertiary nitrates in a protic SOA environment could also act more generally as leaving groups, possibly promoted by the coproduction of HNO 3 in high-NO x experiments which could act as general acid catalyst, 52 leading to non-hydrolysis accretion reactions. D'Ambro et al 18 showed that the thermal desorption characteristics of high-NO x ipSOA, formed at low loadings (<2 μg m −3 ) was consistent with significant lowvolatility content that underwent thermal decomposition during desorption.…”

“…Tertiary nitrates in a protic SOA environment could also act more generally as leaving groups, possibly promoted by the coproduction of HNO 3 in high-NO x experiments which could act as general acid catalyst, leading to non-hydrolysis accretion reactions. D’Ambro et al .…”