Isoprene Epoxydiols as Precursors to Secondary Organic Aerosol Formation: Acid-Catalyzed Reactive Uptake Studies with Authentic Compounds

摘要

Isoprene epoxydiols (LEPOX), formed from the photooxidation of isoprene under low-NO_x conditions, have recently been proposed as precursors of secondary organic aerosol (SOA) on the basis of mass spectrometric evidence. In the present study, LEPOX isomers were synthesized in high purity (>99%) to investigate their potential to form SOA via reactive uptake in a series of controlled dark chamber studies followed by reaction product analyses. lEPOX-derived SOA was substantially observed only in the presence of acidic aerosols, with conservative lawer-bound yields of 4.7-6.4% for β-BPOX and 3.4-5.5* for cS-IEPOX providing direct evidence for LEPOX isomers as precursors to isoprene SOA These chamber studies demonstrate that IEPOX uptake explains the Formation of known isoprene SOA tracers found in ambient aerosols, including 2-merhyttetrols, Cy-alkene trtols, dhners, and LEPOX-derived organosulfates. Additionally, we show reactive uptake on the acidified sulfate aerosols supports a previously unreported acid-catalyzed intramolecular rearrangement of LEPOX to at- and (rans-3 methyltetrahydrofuran-3,4-diols (3-MeTHF-3,4-diols) in the particle phase. Analysis of these novel tracer compounds by aerosol mass spectrometry (AMS) suggests that they contribute to a unique factor resolved from positive matrix factorization (PMF) of AMS organic aerosol spectra collected from low-NO_x, isoprene-dominated regions influenced by the presence of acidic aerosols.