Atmospheric isoprene ozonolysis: impacts of stabilized Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide

Abstract

Abstract. Isoprene is the dominant global biogenic volatile organic compound (VOC) emission. Reactions of isoprene with ozone are known to form stabilised Criegee intermediates (SCIs), which have recently been shown to be potentially important oxidants for SO2 and NO2 in the atmosphere; however the significance of this chemistry for SO2 processing (affecting sulfate aerosol) and NO2 processing (affecting NOx levels) depends critically upon the fate of the SCI with respect to reaction with water and decomposition. Here, we have investigated the removal of SO2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene derived SCI with H2O. Under excess SO2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + H2O)/k(SCI + SO2), of 5.4 (±0.8) × 10−5 for isoprene derived SCI. The relative rate constant for k(SCI decomposition)/k(SCI + SO2) is 8.4 (±5.0) × 1010 cm−3. Uncertainties are ±2σ and represent combined systematic and precision components. These kinetic parameters are based on the simplification that a single SCI species is formed in isoprene ozonolysis, an approximation which describes the results well across the full range of experimental conditions. Our data indicate that isoprene-derived SCIs are unlikely to make a substantial contribution to gas-phase SO2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO2 removal in the isoprene-ozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCI and DMS; the observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + DMS)/k(SCI + SO2), of 4.1 (±2.2). This result suggests that SCIs may contribute to the oxidation of DMS in the atmosphere and that this process could therefore influence new particle formation in regions impacted by emissions of unsaturated hydrocarbons and DMS.

Unimolecular decay strongly limits the atmospheric impact of Criegee intermediates

“…Lifetimes of the order of milliseconds are predicted here, in agreement with literature data, 16,41,[45][46][47][48][49][50][51] and allylresonance (reaction (10)) further increases the reaction rate. These reactions form vinyl hydroperoxides (VHP), where for asymmetric CI the E-VHP is by far the most dominant stereospecific product.…”

Estimating the atmospheric concentration of Criegee intermediates and their possible interference in a FAGE-LIF instrument

“…The rate of this reaction strongly depends on the CI conformation (Aplincourt and Ruiz-López, 2000;Tobias and Ziemann, 2001;Ryzhkov and Ariya, 2003;Kuwata et al, 2010;Anglada et al, 2011;Anglada and Sole, 2016;Chen et al, 2016;Lin et al, 2016;Long et al, 2016) and until now the rate coefficient has been measured for anti-CH 3 CHOO Sheps et al, 2014), while lower limits have been determined for CH 2 OO (Stone et al, 2014), syn-CH 3 CHOO Sheps et al, 2014), and (CH 3 ) 2 COO (Huang et al, 2015;Newland et al, 2015b). The uncertainties in these rate coefficients make it difficult to estimate the importance of Criegee intermediates and the impact they may have as oxidants in the atmosphere.…”

Gas-phase broadband spectroscopy using active sources: progress, status, and applications [Invited]

“…However, higher time resolution can be obtained by using a time-resolved step-scan FTS [199, 200] for repetitive events that can be triggered at a precise time (for example, chemical reactions initiated with laser photolysis). Time-resolved FTS has been used to measure the kinetics of Criegee intermediates, which are formed during the reaction between ozone and alkenes and are thought to be important oxidizers of SO 2 and NO 2 [201–203]. The small Criegee intermediates (CH 2 OO and CH 3 CH 2 OO) formed from the photo-initiated reaction of iodine-substituted hydrocarbons with O 2 were found to have an unexpectedly fast self-reaction rate [204] and conformer-dependent reaction rates in a mixture NO/NO 2 [205].…”