Kinetics of the reaction of the criegee intermediate CH 2 OO with water Rachel E. Lade 1 , Mark A. Blitz 1,2 , Paul W. Seakins 1 , Daniel Stone 1 1 School of Chemistry, University of Leeds, UK, 2 National Centre for Atmospheric Science, University of Leeds, UK Air quality and climate change are influenced by atmospheric composition, which is controlled by both the emissions and chemistry of trace species. Criegee intermediates (CIs) are reactive zwitterionic species with the general formula R 1 R 2 COO that are produced in the atmosphere following the ozonolysis of unsaturated volatile organic compounds (VOCs). The nascent excited Criegee intermediate can undergo unimolecular decomposition to form important trace species such as OH, CO and HO 2 1 or become stabilised via collisions with species such as N 2 and O 2 to form stabilised Criegee intermediates (SCIs). Bimolecular reactions of SCIs with water vapour and SO 2 are of particular interest as they have the potential to impact atmospheric budgets of secondary organic aerosols (SOA), gas phase sulfuric acid, and sulfate aerosol, thereby influencing air quality and climate. Reaction with water vapour is expected to dominate the atmospheric chemistry of the simplest SCI, CH 2 OO, but there is uncertainty over the role of the water monomers (H 2 O, R1) or water dimers ((H 2 O) 2 , R2), with a wide range of values reported for the kinetics of R1 and R2 at room temperature and only one previous study of the temperature dependence of the reaction over a relatively narrow temperature range 2 . The kinetics of the reaction of CH 2 OO with water vapour have been measured experimentally in this work using laser flash photolysis of CH 2 I 2 /O2 /N 2 /H 2 O mixtures coupled with time-resolved broadband ultraviolet absorption spectroscopy as a function of temperature (262 – 353 K). A quadratic relationship was observed between the rate coefficient describing the loss of CH 2 OO and H 2 O, in agreement with previous work 2,3 which suggests that the dominant reaction taking place is that of CH 2 OO and water dimers ((H 2 O) 2 ). Results from this work show that the reaction of CH 2 OO with water dimers has a rate coefficient of (8.14 ± 0.88) × 10 -12 cm 3 molecule -1 s -1 at 298 K, with a temperature dependence described by k 2 = (1.89± 0.27)× 10 -29 × ( T / 298)× exp (12120± 4486 / T ) cm 3 molecule -1 s -1 . Atmospheric implications will be discussed. References
1. D. Johnson, G. Martson., Chem. Soc. Rev., 37 , 699-716, (2008). 2. M. Smith et al., J. Phys. Chem. Lett., 14, 2708-2713, (2015). 3. T. Berndt et al., Phys. Chem. Chem. Phys., 16, 19130-19136, (2014).
P28
© The Author(s), 2023
Made with FlippingBook Learn more on our blog