Abstract
Abstract. Peracetic acid (CH3C(O)OOH) is one of the most abundant organic peroxides in the atmosphere; yet the kinetics of its reaction with OH, believed to be the major sink, have only been studied once experimentally. In this work we combine a pulsed-laser photolysis kinetic study of the title reaction with theoretical calculations of the rate coefficient and mechanism. We demonstrate that the rate coefficient is orders of magnitude lower than previously determined, with an experimentally derived upper limit of 4×10-14 cm3 molec.−1 s−1. The relatively low rate coefficient is in good agreement with the theoretical result of 3×10-14 cm3 molec.−1 s−1 at 298 K, increasing to ∼6×10-14 cm3 molec.−1 s−1 in the cold upper troposphere but with associated uncertainty of a factor of 2. The reaction proceeds mainly via abstraction of the peroxidic hydrogen via a relatively weakly bonded and short-lived prereaction complex, in which H abstraction occurs only slowly due to a high barrier and low tunnelling probabilities. Our results imply that the lifetime of CH3C(O)OOH with respect to OH-initiated degradation in the atmosphere is of the order of 1 year (not days as previously believed) and that its major sink in the free and upper troposphere is likely to be photolysis, with deposition important in the boundary layer.
Highlights
The processes leading to the formation and loss of two classes of atmospheric trace gases, organic acids and organic peroxides, have been the subject of numerous field, laboratory and model-based investigations (Atkinson et al, 2006; Calvert et al, 2011; Gunz and Hoffmann, 1990; Jackson and Hewitt, 1999; Lee et al, 2000; Paulot et al, 2011; Reeves and Penkett, 2003)
The laboratory kinetic studies of the title reactions used the method of pulsed laser photolytic (PLP) generation of OH combined with real time detection based on pulsed laser induced fluorescence (LIF)
H2O2 and organic peroxides (Fischer et al, 2015), we found that H2O2 was present at about 1 % of the CH3C(O)OOH concentration, consistent with the low vapour pressure of H2O2 compared to CH3C(O)OOH
Summary
The processes leading to the formation and loss of two classes of atmospheric trace gases, organic acids and organic peroxides, have been the subject of numerous field, laboratory and model-based investigations (Atkinson et al, 2006; Calvert et al, 2011; Gunz and Hoffmann, 1990; Jackson and Hewitt, 1999; Lee et al, 2000; Paulot et al, 2011; Reeves and Penkett, 2003). Measurements in the boundary layer (Crowley et al, 2018; Fels and Junkermann, 1994; He et al, 2010; Liang et al, 2013; Phillips et al, 2013; Walker et al, 2006; Zhang et al, 2010) and from aircraft (Crounse et al, 2006; Wang et al, 2019) indicate that it is present throughout the troposphere, where it is observed to be the second most abundant organic peroxide (after CH3OOH). Unlike its non-peroxidic analogue, CH3C(O)OH (acetic acid), the direct emission of CH3C(O)OOH by the biosphere has not been documented, and its formation during biomass burning has not been reported (Andreae, 2019), elevated CH3C(O)OOH mixing ratios have been observed in air masses impacted by biomass burning (Crowley et al, 2018; Phillips et al, 2013). Apart from leakage during industrial production and application as an indoor disinfectant (Henneken et al, 2006; Pacenti et al, 2010), the only significant source of CH3C(O)OOH in the atmosphere is the radical terminating channel (Reaction R1a) in the reaction between the acetylperoxy and hydroperoxyl radicals
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