Rate Coefficients of C1 and C2 Criegee Intermediate Reactions with Formic and Acetic Acid Near the Collision Limit: Direct Kinetics Measurements and Atmospheric Implications

Abstract

Rate coefficients are directly determined for the reactions of the Criegee intermediates (CI) CH2OO and CH3CHOO with the two simplest carboxylic acids, formic acid (HCOOH) and acetic acid (CH3COOH), employing two complementary techniques: multiplexed photoionization mass spectrometry and cavity-enhanced broadband ultraviolet absorption spectroscopy. The measured rate coefficients are in excess of 1×10−10 cm3 s−1, several orders of magnitude larger than those suggested from many previous alkene ozonolysis experiments and assumed in atmospheric modeling studies. These results suggest that the reaction with carboxylic acids is a substantially more important loss process for CIs than is presently assumed. Implementing these rate coefficients in global atmospheric models shows that reactions between CI and organic acids make a substantial contribution to removal of these acids in terrestrial equatorial areas and in other regions where high CI concentrations occur such as high northern latitudes, and implies that sources of acids in these areas are larger than previously recognized.

Reactivity of stabilized Criegee intermediates (sCIs) from isoprene and monoterpene ozonolysis toward SO<sub>2</sub> and organic acids

“…Acid formation yields are about 5 % of reacted alkene, and thus the acid concentrations are in the range of 10 7 molecules cm −3 (4-7 orders of magnitude lower than the SO 2 concentrations). The relative reactivity, k(sCI + acid) / k(sCI + SO 2 ), is ∼ 3 as shown later in this work and qualitatively in line with Welz et al (2014). Thus, sCI + acid cannot be competitive with sCI + SO 2 in this experiment.…”

“…Neeb et al (1997) showed that the rate coefficient for the above reaction is relatively large (14 000-fold) in comparison to the reaction rate coefficient for CH 2 OO + water. An extremely high reactivity of CH 2 OO and CH 3 CHOO toward formic (HCOOH) and acetic acid (CH 3 COOH) was observed also by Welz et al (2014) in a low-pressure system. Also Taatjes et al (2012; showed that sCIs -at least the simple sCIs -are reactive toward other trace gases in addition to SO 2 .…”

“…Due to the relatively long lifetime of sCI, bimolecular reactions of sCIs with several compounds like water vapour, SO 2 , carbonyls, organic acids, etc., are also possible (e.g. Neeb et al, 1996Neeb et al, , 1997Johnson, 2001;Welz et al, 2012Welz et al, , 2014Mauldin III et al, 2012;Berndt et al, 2012Berndt et al, , 2014aTaatjes et al, 2012Taatjes et al, , 2013. These reactions can potentially be fast enough to contribute significantly to the atmospheric oxidation capacity.…”

Role of the reaction of stabilized Criegee intermediates with peroxy radicals in particle formation and growth in air

“…It can be seen in Fig. 2b and c that the presence of formic acid, which reacts with SCI, 5,45,[66][67][68] strongly suppresses the formation of longer oligomers, confirming that SCI play a key role in oligomer formation.…”

“…In addition, SCI react with a number of other atmospheric species, e.g., H 2 O, SO 2 , NO 2 , carboxylic acids, as well as carbonyl and hydroxyl compounds. 5,45,[66][67][68]72,[93][94][95] Bimolecular reactions with these scavengers, in particular H 2 O, have been suggested to be the dominant loss pathway of some SCIs in the atmosphere. 45,67,72 However, in the present study, water vapor was shown to increase new particle formation while decreasing the total mass.…”