Impact of Glycol Ether Structure on OH-Initiated Oxidation and Resulting Aerosol Formation
TUCKER MELLES, Audrey Lawrence, Cort Zang, Abraham Dearden, Katelyn Rediger, Huiying Luo, Masoud Akbarzadeh, Amel Ksaibati, Damien Ketcherside, Lu Tan, Matthew Coggon, Chelsea Stockwell, Lu Xu, Ann M. Middlebrook, Alison Piasecki, Lauren A. Garofalo, Carsten Warneke, Lu Hu, Delphine K. Farmer, Shantanu Jathar, Megan Willis, Colorado State University
Abstract Number: 282
Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts
Abstract
Glycol ethers are a class of volatile organic compounds (VOCs) emitted from volatile chemical products (VCPs), which are contributors to secondary organic aerosol (SOA) in urban environments. Glycol ethers are used in dyes, resins, and cleaning products and are estimated to account for 1-2% of VCP VOC emissions in California. Reported SOA mass yields range from < 0.1% to over 30%, motivating investigation into how molecular structure and environmental conditions (e.g., HO2 and NO concentrations) impact SOA formation from glycol ether oxidation. We present results from the Secondary organic aerosol Chamber Experiments on Non-Traditional Species (SCENTS) project examining SOA formation from OH-initiated glycol ether oxidation. We use online mass spectrometry to monitor gas and particle phase composition. In our experiments, linear glycol ethers display higher SOA mass yields than branched glycol ethers of similar carbon number. We combine our observations, literature, and previously reported structure-activity relationships to construct oxidation mechanisms for both linear and branched glycol ethers. We find that the glycol ether oxygen-containing functional groups, together with the presence of branched structures, control oxidation-induced carbon-carbon bond scission. Glycol ether RO2 fate dictates SOA production, with hydroperoxide production (via RO2 + HO2) promoted by our chamber conditions significantly contributing to SOA mass. Conversely, RO2 + NO reactions generate fragmentation-prone RO radicals because ether and hydroxyl groups in glycol ethers drive carbon-carbon bond scission independent of structure. Instead, differences in SOA mass yield with glycol ether structure likely arise from available RO2 reaction pathways. Reaction of ether-adjacent RO2 with HO2 may produce carbonyls or hydroperoxides; however, the carbonyl pathway is not available to tertiary-RO2, potentially increasing the competitiveness of RO2 + NO reactions that promote fragmentation. Glycol ether RO2 fate and SOA production depend on molecular structure and bimolecular reactant concentrations, with branching structures and NO promoting carbon-carbon scission and reducing SOA mass yields.