The atmospheric impacts of monoterpene ozonolysis on global stabilised Criegee intermediate budgets and SO<sub>2</sub> oxidation: experiment, theory and modelling

Abstract

21The gas-phase reaction of alkenes with ozone is known to produce stabilised Criegee 22 intermediates (SCIs). These biradical/zwitterionic species have the potential to act as 23 atmospheric oxidants for trace pollutants such as SO 2 , enhancing the formation of sulfate 24 aerosol with impacts on air quality and health, radiative transfer and climate. However, the 25 importance of this chemistry is uncertain as a consequence of limited understanding of the 26 abundance and atmospheric fate of SCIs. In this work we apply experimental, theoretical and 27 numerical modelling methods to quantify the atmospheric impacts, abundance, and fate, of 28 Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1095 Manuscript under review for journal Atmos. Chem. Phys.

Sulfur Dioxide Modifies Aerosol Particle Formation and Growth by Ozonolysis of Monoterpenes and Isoprene

“…We note that the RH used in our study (15 ± 3%) was above this level, and so the extent of SO 2 oxidation would likely be similar under higher RH representative of ambient conditions. We also note that the syn ‐sCI yields proposed by Newland et al () increase in the order α ‐pinene < limonene < β ‐pinene, which is in agreement with the amount of nucleation we observe in our experiments following SO 2 addition.…”

“…Particle nucleation was also observed with β ‐pinene in the presence of SO 2 , and the number concentration was about a factor of 5 higher than that achieved with α ‐pinene for approximately the same number of molecules oxidized. This suggests that the yield of H 2 SO 4 produced by oxidation of SO 2 during β ‐pinene ozonolysis is much greater than from α ‐pinene ozonolysis, which is in line with a reported higher sCI yield from β ‐pinene than α ‐pinene (Hatakeyama & Akimoto, ; Newland et al, ). Due to this substantial new particle formation, the seed particles only contributed less than 10% to the total condensation sink after SO 2 addition.…”

“…Numerous studies have suggested that the dominant fate of the smallest sCI (CH 2 OO) is reaction with water (Berndt et al, ; Chao et al, ; Newland et al, ), whereas larger sCIs, such as those produced by ozonolysis of monoterpenes, can be less reactive to water, in particular the syn conformers (Sheps et al, ; Taatjes et al, ). Newland et al () recently studied the loss of SO 2 during ozonolysis of the same three monoterpenes studied in this work as a function of relative humidity. They found that as RH was increased, the SO 2 loss became less sensitive to [H 2 O], which they attributed to there being at least two chemically distinct sCIs produced from each monoterpene (i.e., anti and syn ).…”

“…Isoprene has been previously reported to give a significantly higher total yield of sCIs from its reaction with ozone relative to α ‐pinene or limonene (Sipilä et al, ). Our results then suggest that only a fraction of the total isoprene sCI yield reacts with SO 2 , with the remainder likely scavenged by water vapor, which once again is likely to occur rapidly even at a fairly low relative humidity of ~15% as used in this study (Newland et al, ).…”

Criegee intermediates and their impacts on the troposphere

“…26 36 Newland et al 36 Newland et al 36 Note: the experimental first order rate coefficients include a component from wall loss of the Criegee intermediate in addition to unimolecular decomposition, *the wall loss was negligible in the work of Kroll et al 9 because of using large diameter reactor, **the wall loss (assuming equal to thermal decomposition of CH2OO) was accounted for in the work of Smith et al 35 . MVKOO represents methyl vinyl carbonyl oxide and MACROO represents methacrolein oxide which are isoprene derived sCIs.…”