Isoprene is a major source of secondary organic aerosol (SOA). Improving our fundamental understanding of isoprene-derived SOA is key to improving existing air quality models, especially since these models currently underestimate observations. By combining organic synthesis, computational calculations, mass spectrometry, smog chamber studies, flow tube studies and field measurements, we show that reactive epoxides, which include methacrylic acid epoxide (MAE) and isomeric isoprene epoxydiols (IEPOX), produced from the atmospheric oxidation of isoprene are key to SOA formation. Furthermore, anthropogenic pollutants enhance these epoxides as an SOA source. In the laboratory, we find that the reactive uptake of synthetic IEPOX and MAE standards onto acidified sulfate aerosol yields known isoprene-derived SOA tracers (2-methlytetrols, 2-methylglyceric acid, C5-alkene triols, 3-methyltetrahydrofuran-3,4-diols, dimers and organosulfates) that we measure in fine aerosol collected from multiple sites across the southeastern U.S. using gas chromatography/mass spectrometry (GC/MS) and liquid chromatography coupled to diode array detection and electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (LC/DAD-ESI-QTOFMS). Notably, IEPOX- and MAE-derived SOA molecular tracers account for a significant mass fraction (10-20%) of ambient OA. Moreover, real-time continuous chemical measurements of fine aerosol made using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) during summer 2011 and 2013 resolved IEPOX-derived SOA when applying positive matrix factorization (PMF) to the organic mass spectral time series. IEPOX-derived SOA is found to account for upwards of 33% of the fine OA mass and is correlated with known molecular tracers, sulfate, and aerosol acidity. We have investigated the heterogeneous kinetics of MAE and trans-b-IEPOX. The reaction probability, also called the reactive uptake coefficient, is calculated for MAE and IEPOX on 1-2 component aerosol particles under various aerosol compositions and environmental conditions in order to probe the chemical drivers of the epoxide uptake. New findings on how this chemistry impacts climate and public health will also be discussed.

Anthropogenic pollutants enhance secondary organic aerosol production from the heterogeneous chemistry of isoprene-derived epoxides: Implications for air quality, climate, and public health in the southeastern U.S.

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.