Publication: Atmospheric fates of Criegee intermediates in the ozonolysis of isoprene

Publication - Atmospheric fates of Criegee intermediates in the ozonolysis of isoprene

Title: Atmospheric fates of Criegee intermediates in the ozonolysis of isoprene
DOI: 10.1039/C6CP00053C
Publication Year: 2015
Author list: Nguyen, T. B.; Tyndall, G. S.; Crounse, J. D.; Teng, A. P.; Bates, K. H.; Schwantes, R. H.; Coggon, M. M.; Zhang, L.; Feiner, P.; Miller, D. O.; Skog, K. M.; Rivera-Rios, J. C.; Dorris, M.; Olson, K. F.; Koss, A.; Wild, R. J.; Brown, S. S.; Goldstein, A.
Journal Short Name: Phys. Chem. Chem. Phys.
Publisher: RSC

We use a large laboratory, modeling, and field dataset to investigate the isoprene + O3 reaction, with the goal of better understanding the fates of the C1 and C4 Criegee intermediates in the atmosphere. Although ozonolysis can produce several distinct Criegee intermediates, the C1 stabilized Criegee (CH2OO, 61 ± 9%) is the only one observed to react bimolecularly. We suggest that the C4 Criegees have a low stabilization fraction and propose pathways for their decomposition. Both prompt and non-prompt reactions are important in the production of OH (28% ± 5%) and formaldehyde (81% ± 16%). The yields of unimolecular products (OH, formaldehyde, methacrolein (42 ± 6%) and methyl vinyl ketone (18 ± 6%)) are fairly insensitive to water, i.e., changes in yields in response to water vapor (≤4% absolute) are within the error of the analysis. We propose a comprehensive reaction mechanism that can be incorporated into atmospheric models, which reproduces laboratory data over a wide range of relative humidities. The mechanism proposes that CH2OO + H2O (k(H2O) ∼ 1 × 10−15 cm3 molec−1 s−1) yields 73% hydroxymethyl hydroperoxide (HMHP), 6% formaldehyde + H2O2, and 21% formic acid + H2O; and CH2OO + (H2O)2 (k(H2O)2 ∼ 1 × 10−12 cm3 molec−1 s−1) yields 40% HMHP, 6% formaldehyde + H2O2, and 54% formic acid + H2O. Competitive rate determinations (kSO2/k(H2O)n=1,2 ∼ 2.2 (±0.3) × 104) and field observations suggest that water vapor is a sink for greater than 98% of CH2OO in a Southeastern US forest, even during pollution episodes ([SO2] ∼ 10 ppb). The importance of the CH2OO + (H2O)n reaction is demonstrated by high HMHP mixing ratios observed over the forest canopy. We find that CH2OO does not substantially affect the lifetime of SO2 or HCOOH in the Southeast US, e.g., CH2OO + SO2 reaction is a minor contribution (<6%) to sulfate formation. Extrapolating, these results imply that sulfate production by stabilized Criegees is likely unimportant in regions dominated by the reactivity of ozone with isoprene. In contrast, hydroperoxide, organic acid, and formaldehyde formation from isoprene ozonolysis in those areas may be significant.

Additional Notes
Some FIXCIT experiments were used in this analysis

Experiments (3)

ID Name Start date Experiment Category Reaction Type Reactant(s) Oxidant Name Temperature Humidity Type of Seed RO2 Main Fate Data Sets (count) Actions
94 2014 FIXCIT Study_20140106_Isoprene/Ozone/Water_Hydroxyl radical_No Seed_Isoprene + OH + O3, low NO, dry, no seeds 2014-01-06 Gas phase chemical reaction Photooxidation Isoprene, Ozone, Water Hydroxyl radical 25 5 No Seed HO2 11 Download
406 2014 FIXCIT Study_20140123_ISOPRENE/OZONE_Hydroxyl radical_No Seed_Isoprene + OH + O3, low NO, 50% humidity, no seeds 2014-01-23 Gas phase chemical reaction Photooxidation ISOPRENE, OZONE Hydroxyl radical 25 50 HO2 13 Download
409 2014 FIXCIT Study_20140129_isoprene/ozone/CYCLOHEXANE_Ozone_No Seed_Isoprene + O3, cyclohexane OH scrubber, 50% humidity, no seeds 2014-01-29 Gas phase chemical reaction Photooxidation isoprene, ozone, CYCLOHEXANE Ozone 25 58 Not Sure 13 Download