Gas-Phase Oxidation Rates and Products of 1,2-Dihydroxy Isoprene

1,2-Dihydroxy isoprene (1,2-DHI), a product of isoprene oxidation from multiple chemical pathways, is produced in the atmosphere in large quantities; however, its chemical fate has not been comprehensively studied. Here, we perform chamber experiments to investigate its gas-phase reactions. We find that the reactions of 1,2-DHI with OH radicals and ozone are rapid (k(OH) = 8.0 (+/- 1.3) x 10(-11) cm(3) molecule(-1) s(-1); k(O3) = 7.2 (+/- 1.1) x 10(-18) cm3 molecule-1 s-1). Reaction with OH, which dominates 1,2-DHI loss, leads primarily to fragmentation and radical recycling; major products under both high- and low-NO conditions include hydroxyacetone, glycolaldehyde, and 2,3-dihydroxy-2-methyl-propanal (DHMP). Radical-terminating hydroperoxide formation from the peroxy radical (RO2) reaction with HO2 and organonitrate formation from RO2 + NO are not observed in the gas phase, possibly due to low volatility; constraints for their branching ratios are instead derived by mass balance. We also measure secondary organic aerosol mass yields from 1,2-DHI (0-23%) and show that oxidation in the presence of aqueous particles leads to formic and acetic acid production. Finally, we incorporate results into GEOS-Chem, a global chemical transport model, to compute the global production (25.3 Tg a(-1)) and gas-phase loss (20.2 Tg a(-1)) of 1,2-DHI and show that its oxidation provides non-negligible contributions to the atmospheric budgets of hydroxyacetone, glycolaldehyde, hydroxymethyl hydroperoxide, formic acid, and DHMP.

Automated summary

This study investigates the gas-phase reactions of 1,2-Dihydroxy isoprene (1,2-DHI) with OH radicals and ozone, finding rapid reactions and major products like hydroxyacetone, glycolaldehyde, and 2,3-dihydroxy-2-methyl-propanal (DHMP). Formation of radical-terminating hydroperoxide and organonitrate from RO2 reactions are not observed in gas phase due to low volatility, leading to branching ratios being derived by mass balance. Incorporating results into a global chemical transport model shows significant contributions of 1,2-DHI oxidation to atmospheric budgets of various compounds.