Analytical Chemistry Seminar: Jordan Krechmer
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program
Formation of Low Volatility Compounds and SOA from Isoprene Oxidation without IEPOX uptake
Jordan Krechmer - 3rd Year Graduate Studentl, Department of Chemistry and Biochemistry
Many of the sources and formation mechanisms of secondary organic aerosol (SOA) are still poorly understood. In this talk, I will present evidence of gas-phase low volatility organic compounds (LVOC), produced from the OH oxidation of isoprene hydroxy hydroperoxide (ISOPOOH), condensing and forming secondary organic aerosol (SOA) during the Caltech FIXCIT chamber study. Decreases in LVOC concentrations directly corresponded to the appearance and growth in organic aerosol, indicating that LVOC were condensing and forming SOA (at OA levels below 1 mg m-3) with a wall-loss corrected mass yield of roughly 1.5% (from isoprene). This previously uncharacterized formation pathway from isoprene could account for up to 8.0 Tg yr-1 of SOA, or 5% of the estimated global SOA source. The experimental conditions and AMS SOA spectrum indicate that SOA formation in this study is separate and not explained by previously described IEPOX uptake. Condensing species have 4-5 carbons and volatilities consistent with multiple hydroxyl groups, as well as carbonyl and possibly hydroperoxide groups. These species are not extremely low volatility VOCs (ELVOC) as previously observed from monoterpene oxidation by O3, but most likely LVOC with saturation concentrations ranging from 10-2 to 10mg m-3. Their ability to condense at low OA levels at room temperature and to grow nanoparticles indicate that their importance may be largest in environments with lower OA concentrations. The same LVOC compounds were observed in the atmosphere during the SOAS campaign in the SE US. The results of efforts to extract mechanistic information from an ion mobility spectrometer-mass spectrometer (IMS-MS) during the SOAS field study and subsequent laboratory work will also be presented.