Atmospheric isoprene ozonolysis: impacts of stabilised 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 SO 2 and NO 2 in the atmosphere; however the significance of this chemistry for SO 2 processing (affecting sulfate aerosol) and NO 2 processing (affecting NO x levels) depends critically upon the fate of the SCIs with respect to reaction with water and decomposition. Here, we have investigated the removal of SO 2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO 2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene-derived SCIs with H 2 O. Under excess SO 2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO 2 removal kinetics are consistent with a relative rate constant, k(SCI + H 2 O) / k(SCI + SO 2 ), of 3.1 (±0.5) × 10 −5 for isoprene-derived SCIs. The relative rate constant for k(SCI decomposition) / k(SCI+SO 2 ) is 3.0 (±3.2) × 10 11 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 isoprenederived SCIs are unlikely to make a substantial contribution to gas-phase SO 2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO 2 removal in the isopreneozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCIs and dimethyl sulfide (DMS); the observed SO 2 removal kinetics are consistent with a relative rate constant, k(SCI + DMS) / k(SCI + SO 2 ), of 3.5 (±1.8). 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.

An Estimation of the Levels of Stabilized Criegee Intermediates in the UK Urban and Rural Atmosphere Using the Steady-State Approximation and the Potential Effects of These Intermediates on Tropospheric Oxidation Cycles

“…sCI was then split into CI‐1 (CH 2 OO), CI‐2 (RCHOO), and CI‐3 (R 2 COO). Taking account of the unimolecular loss rate ( k 2 ) of 11.6 s −1 for CI‐1 , 250 s −1 for CI‐2 , and 305 s −1 for CI‐3 , the rate coefficient of the reaction with H 2 O ( k 3 ) of 2.4 × 10 −16 cm 3 molecules −1 s −1 for CI‐1 , 1.9 × 10 −19 cm 3 molecules −1 s −1 for syn ‐CI‐2 , 5.2 × 10 −15 cm 3 molecules −1 s −1 for anti ‐CI‐2 , and 2.1 × 10 −15 cm 3 molecules −1 s −1 for CI‐3 , the rate coefficient of the reaction of CH 2 OO with (H 2 O) 2 ( k 4 ) of 5.4 × 10 −12 cm 3 molecules −1 s −1 for CI‐1 , 2.6 × 10 −14 cm 3 molecules −1 s −1 for syn ‐CI‐2 , 1.6 × 10 −11 cm 3 molecules −1 s −1 for anti ‐CI‐2 , and 1.3 × 10 −13 cm 3 molecules −1 s −1 for CI‐3 , the loss process of sCI was estimated. The monthly average [H 2 O], [(H 2 O) 2 ], and temperature data (Supporting Information, Table S2) were obtained from UK Meteorological office chemistry transport model, STOCHEM (Dick Derwent, Personal communication).…”

Investigation of potential interferences in the detection of atmospheric RO<sub><i>x</i></sub> radicals by laser-induced fluorescence under dark conditions

“…The sCI yield for molecules which give internal OH production has been determined to be 15 % for α-pinene, 27 % for limonene, and 58 % for isoprene Donahue et al, 2011;Newland et al, 2015b). The chemistry of the sCI is diverse and is subject to recent research that has been summarized in recent reviews (Taatjes et al, 2014;Lee, 2015).…”

Unimolecular decomposition kinetics of the stabilised Criegee intermediates CH2OO and CD2OO

“…A recent series of chamber experiments at atmospheric temperature and pressure reported an upper limit of 4.2 s À1 for the first-order loss of stabilised CH 2 OO, which includes a contribution from the decomposition reaction. 19,20 This value was determined by measuring the ratio of the rate coefficient for first-order losses to that for the reaction of CH 2 OO with SO 2 , and the decomposition rate was indistinguishable from zero within the measurement uncertainties. 19,20 Measurements of photolytically generated CH 2 OO using cavity ringdown spectroscopy (CRDS) have also been used to infer the unimolecular decomposition kinetics in N 2 at 293 K in the pressure range 7 to 30 Torr, giving an upper limit to the decomposition rate coefficient of (11.6 AE 8.0) s À1 .…”