Understanding unique aqueous glyoxal chemistry leading to formation of secondary organic aerosol
EMSL Project ID
47858
Abstract
Atmospheric aerosols cool climate by scattering incoming solar radiation, and by modifying cloud cover and thus Earth albedo. Organic aerosol (OA) forms a major fraction of aerosol mass in the atmosphere. Most OA forms from the oxidation of gases in the atmosphere as secondary organic aerosols (SOA). SOA formation remains poorly understood, and is not usually studied at the molecular level. Instead, most SOA models currently parameterize SOA by means of the so-called volatility basis set (VBS). While these parameterizations have allowed for considerable advances in recent years to predict OA mass close to correctly, these models predict incorrect chemical properties of OA, such as underestimating the atomic oxygen to carbon ration (O/C), indicating that the mass is correct for the wrong reasons. Understanding SOA formation mechanisms at the molecular level is of critical importance to predict SOA accurately in the atmosphere.Glyoxal is a ubiquitous component of air in terrestrial biogenic, urban, arctic, and remote marine environments, and a precursor for SOA via multiphase chemistry in clouds and aerosol water. Observations of glyoxal in aerosols remain as yet unexplained by most atmospheric models. We propose to study SOA formation from glyoxal at the molecular level. By studying the reaction mechanism of glyoxal-SOA formation this proposal also guides research on other molecules that form SOA via aqueous and multiphase chemical reactions.
As part of ongoing and funded effort to understand SOA formation from glyoxal, we are conducting a seven week international campaign at the Paul Scherrer Institut in Switzerland in May/June 2013. This campaign builds on our previous experiences with conducting simulation chamber experiments, where we have shown that a single parameter, the salting constant, describes our observations that the glyoxal monomer partitioning to aerosols increases exponentially with salt concentration. Activity coefficients of ~1000 are caused by electrical interactions of glyoxal with sulfate ions. The campaign this summer seeks to understand how this increased partitioning depends on seed chemical composition and aerosol pH. In particular, we hypothesize that other anions strongly effect the partitioning of glyoxal to the aerosol phase as well, and are poised to explore the effects of these electrostatic interactions on glyoxal reactivity in aerosols. A large data set will be collected as part of which we plan to collect MOUDI filter samples. Here we propose to analyze these filter samples using the nano-DESI/HR-MS at EMSL. The focus of the nano-DESI/HR-MS analysis is to identify the products formed in the aerosol phase at the molecular level (i.e., oligomers, organic nitrogen-, and organic sulfur-containing molecules) and see how the relative product ratios respond to changes in the aerosol seed composition and aerosol pH. These measurements are supplementary to on-line quantitative aerosol composition measurements of total organic mass, which retain virtually no molecular information. The molecular level understanding of reaction products will then be compared to predictions from an explicit aqueous-phase glyoxal-SOA model that we have developed over recent years. The data generated by this proposal will directly serve to test and refine this model. This proposal is in direct response to the EMSL call for molecular level understanding of the formation and evolution of atmospheric aerosols.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2013-10-01
End Date
2015-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members