Secondary Organic Aerosol from Aqueous Reactions of Green Leaf Volatiles with Organic Triplet Excited States and Singlet Molecular Oxygen

摘要

Vegetation emits a class of oxygenated hydrocarbons - the green leaf volatiles (GLVs) - under stress or damage. Under foggy conditions GLVs might be a source of secondary organic aerosol (SOA) via aqueous reactions with hydroxyl radical (OH), singlet oxygen (~1O_2~*), and excited triplet states (~3C~*). To examine this, we determined the aqueous kinetics and SOA mass yields for reactions of ~3C~* and ~1O_2~* with five GLVs: methyl jasmonate (MeJa), methyl salicylate (MeSa), cis-3-hexenyl acetate (HxAc), cis-3-hexen-1-ol (HxO), and 2-methyl-3-butene-2-ol (MBO). Second-order rate constants with ~3C~* and ~1O_2~* range from (0.13-22) × 10~8 M~(-1) s~(-1) and (8.2-60) × 10~5 M~(-1) s~(-1) at 298 K, respectively. Rate constants with ~3C~* are independent of temperature, while values with ~1O_2~* show significant temperature dependence (E_a = 20-96 kJ mol~(-1)). Aqueous SOA mass yields for oxidation by ~3C~* are (84 ± 7)%, (80 ± 9)%, and (38 ± 18)%, for MeJa, MeSa, and HxAc, respectively; we did not measure yields for other conditions because of slow kinetics. The aqueous production of SOA from GLVs is dominated by ~3C~* and OH reactions, which form low volatility products at a rate that is approximately half that from the parallel gas-phase reactions of GLVs.