Production and Fate of C_4 Dihydroxycarbonyl Compounds from Isoprene Oxidation

摘要

Isoprene epoxydiols (IEPOX) are formed in high yield as second-generation products of atmospheric isoprene oxidation in pristine (low-NO) environments. IEPOX has received significant attention for its ability to form secondary organic aerosol, but the fate of IEPOX in the gas phase, and those of its oxidation products, remains largely unexplored. In this study, three dihydroxycarbonyl compounds with molecular formula of C_4H_8O_3, putative products of IEPOX oxidation, are synthesized to determine their isomer-specific yields from IEPOX. We find that 3,4-dihydroxy-2-butanone (DHBO) comprises 43% and 36% of the products from cis- and trans-β-IEPOX, respectively, and is by far the most abundant C_4H_8O_3 dihydroxycarbonyl compound produced by this mechanism. OH is found to react with DHBO with a rate coefficient of 1.10 × 10^(–11) cm^3 molecule^(–1) s^(–1) at 297 K, forming two hydroxydicarbonyl compounds that share the molecular formula C_4H_6O_3 with unitary yield. The results of this study are compared with field observations and used to propose a multigenerational mechanism of IEPOX oxidation. Finally, global simulations using GEOS-Chem, a chemical transport model, show that the C_4H_8O_3 dihydroxycarbonyl compounds and their oxidation products are widespread in the atmosphere and estimate annual global production of C_4H_8O_3 dihydroxycarbonyls to be 54 Tg y^(–1), primarily as DHBO.