Laboratory simulation for the aqueous OH-oxidation of methyl vinyl ketone and methacrolein: significance to the in-cloud SOA production

Abstract

Increasing evidence suggests that secondary organic aerosol (SOA) is formed through aqueous phase reactions in atmospheric clouds. In the present study, the aqueous oxidation of methyl vinyl ketone (MVK) and methacrolein (MACR) via OH radical were investigated, with an emphasis on the composition and variation of small-molecular-weight organic products. In addition, high-molecular-weight compounds (HMWs) were found, interpreted as the ion abundance and time evolution. Our results provide, for the first time to our knowledge, experimental evidence that aqueous OH-oxidation of MVK contributes to SOA formation. Further, a mechanism primarily involving radical processes was proposed to gain a basic understanding of these two reactions. Based on the assumed mechanism, a kinetic model was developed for comparison with the experimental results. The model reproduced the observed profiles of first-generation intermediates, but failed to simulate the kinetics of most organic acids mainly due to the lack of chemical kinetics parameters for HMWs. A sensitivity analysis was performed in terms of the effect of stoichiometric coefficients for precursors on oxalic acid yields and the result indicates that additional pathways involving HMWs chemistry might play an important role in the formation of oxalic acid. We suggest that further study is needed for better understanding the behavior of multi-functional products and their contribution to the oxalic acid formation

Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies

“…Carlton et al, 2007;El Haddad et al, 2009;Lim et al, 2010;Perri et al, 2010). Maximum aqSOA yields of up to 100 % from aqueous phase glyoxal and nearly 70 % from aqueous phase methylglyoxal have been reported; aqSOA yields for aqueous MACR and MVK are significantly smaller with 2-12 % and 5-10 %, respectively Zhang et al, 2010). In all experiments, aqSOA yields were observed to be timedependent with an initial increase and a later decrease due to oxidation of aqSOA products to CO 2 .…”

“…Direct contributions of MVK and MACR to aqSOA are not included in the current model approach. These latter products are not very water-soluble but have shown to form aqSOA once dissolved Noziere et al, 2010b;Zhang et al, 2010). Their vapor pressure is also reasonably low that they might form gasSOA and thus are partially captured by P1 and P2 (Eq.…”

“…In ambient aerosol particles and cloud droplets, the observed bulk processes will have only a minor importance due to the limited solubility of these aqSOA precursors; however, in the same study it was discussed that surface reactions could occur and contribute more to organic processing and aqSOA formation. Aqueous oxidation experiments with MACR and MVK show that small acids comprise up to 8.8 % and 23.8 %, respectively, of the aqSOA yield (defined as mass concentration of aerosol after 7 h, related to the initial aqueous phase MACR and MVK concentrations, Zhang et al, 2010). The value for MACR is in good agreement with experiments over longer time scales that reported aqSOA --Absorbing products (l ∼ 500 nm) Spectra structure depending on organic Chang and Thompson (2010) * These rate constants are used in the box model studies in Sect.…”

Understanding the aqueous phase ozonolysis of isoprene: distinct product distribution and mechanism from the gas phase reaction

“…Recently, Hullar and Anastasio (2011) found that the OH-initiated oxidation of organic compounds in aqueous solutions could, in turn, produce H 2 O 2 . Therefore, the aqueous isoprene reaction with ozone appears to initiate a cycle of H 2 O 2 −OH radical, which potentially enhances the formation of aqueous SOA considering that H 2 O 2 and OH radicals are important aqueous oxidants for organic compounds (Carlton et al, 2006;Zhang et al, 2010;Ervens et al, 2011;Huang et al, 2011;Liu et al, 2012;Tan et al, 2012). In addition, peroxide can oxidize S(IV) into S(VI); this increases the aqueous phase acidity, and thus in favor of SOA formation from isoprene oxidation (Surratt et al, 2007).…”

“…However, it remains difficult to quantify the reaction products. Alternatively, a series of recent laboratory experiments on the aqueous oxidation of psVOCs in bulk water in the absence of gas phase interference were performed to quantitatively determine the effect of condensed water on the distribution of products that formed in the aqueous reaction of several psVOCs Zhang et al, 2009Zhang et al, , 2010Huang et al, 2011;EI Haddad et al, 2009;Liu et al, 2012). Interestingly, those studies revealed that the production of carbonyls, organic acids, and peroxides in the aqueous ozonolysis of α-pinene, β-pinene, methacrolein (MAC), and methyl vinyl ketone (MVK), and the aqueous OH radical-initiated oxidation of isoprene, MAC, and MVK significantly differed from those observed in the corresponding gas phase reaction.…”