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

Abstract

Abstract. Oxidation processes in Earth's atmosphere are tightly connected to many environmental and human health issues and are essential drivers for biogeochemistry. Until the recent discovery of the atmospheric relevance of the reaction of stabilized Criegee intermediates (sCIs) with SO 2 , atmospheric oxidation processes were thought to be dominated by a few main oxidants: ozone, hydroxyl radicals (OH), nitrate radicals and, e.g. over oceans, halogen atoms such as chlorine. Here, we report results from laboratory experiments at 293 K and atmospheric pressure focusing on sCI formation from the ozonolysis of isoprene and the most abundant monoterpenes (α-pinene and limonene), and subsequent reactions of the resulting sCIs with SO 2 producing sulfuric acid (H 2 SO 4 ). The measured total sCI yields were (0.15 ± 0.07), (0.27 ± 0.12) and (0.58 ± 0.26) for α-pinene, limonene and isoprene, respectively. The ratio between the rate coefficient for the sCI loss (including thermal decomposition and the reaction with water vapour) and the rate coefficient for the reaction of sCI with SO 2 , k(loss) / k(sCI + SO 2 ), was determined at relative humidities of 10 and 50 %. Observed values represent the average reactivity of all sCIs produced from the individual alkene used in the ozonolysis. For the monoterpene-derived sCIs, the relative rate coefficients k(loss) / k(sCI + SO 2 ) were in the range (2.0-2.4) × 10 12 molecules cm −3 and nearly independent of the relative humidity. This fact points to a minor importance of the sCI + H 2 O reaction in the case of the sCI arising from α-pinene and limonene. For the isoprene sCIs, however, the ratio k(loss) / k(sCI + SO 2 ) was strongly dependent on the relative humidity. To explore whether sCIs could have a more general role in atmospheric oxidation, we investigated as an example the reactivity of acetone oxide (sCI from the ozonolysis of 2,3-dimethyl-2-butene) toward small organic acids, i.e. formic and acetic acid. Acetone oxide was found to react faster with the organic acids than with SO 2 ; k(sCI + acid) / k(sCI + SO 2 ) = (2.8 ± 0.3) for formic acid, and k(sCI + acid) / k(sCI + SO 2 ) = (3.4 ± 0.2) for acetic acid. This finding indicates that sCIs can play a role in the formation and loss of other atmospheric constituents besides SO 2 .

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

“…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.…”

“…Moreover, in some circumstances scavenging of SCI may not necessarily suppress particle formation. For example, in the presence of SO 2 , the reactions between SCI and SO 2 can lead to the formation of H 2 SO 4 , 5,74,93,96,97 an important nucleation precursor. 98,99 A quantitative evaluation of the atmospheric importance of RO 2 + SCI reactions is not possible at the moment because of the large uncertainties in the rate constants for bimolecular reactions of SCI, 45,67 especially those of RO 2 + SCI reactions for which experimental data are not available.…”

Measurement-model comparison of stabilized Criegee Intermediate and Highly Oxygenated Molecule production in the CLOUD chamber

“…Those measurements were conducted at 50% relative humidity (RH) and the derived sCI yield from the reaction between α-pinene and ozone was determined to be 0.15±0.07 and the ratio between the loss term 25 and ksCI+SO2 was (2.0±0.4) ×10 12 molecules cm -3 . Sipilä et al (2014) also found that in the case of α-pinene and limonene the ratio kloss / ksCI+SO2 was nearly independent of the relative humidity therefore we neglected the difference in RH of the experiments shown here (38%) compared to the experiments at TROPOS-LFT (50%). The temperature was 278 K in the CLOUD experiments whereas it was 293 K in the previous experiments.…”

“…Recent studies (Berndt et al, 2012;Mauldin III et al, 2012;Welz et al, 2012) with new experimental methods have shown up to four orders of magnitude higher reaction rate constants for the reaction between a sCI and SO2 compared to previous estimates. Also differences between the reactivity of sCI derived from different alkenes and their reactivity towards 5 SO2, water and several other atmospheric compounds has been emphasized (Berndt et al, 2014a;Sipilä et al, 2014;Taatjes et al, 2013;Vereecken et al, 2012Vereecken et al, , 2014.…”

“…The modelling of HOM concentration was based on the experimental yield terms obtained from recent studies by and Jokinen et al (2015) while the sulphuric acid concentration was modelled using the reaction coefficient and the yield term from the study by Sipilä et al (2014). In addition, we calculated the yield terms for sCI and HOM formation in the CLOUD experiments by fitting our model to the measured sulphuric acid and HOM 35 concentrations.…”