Aqueous-phase oligomerization of methyl vinyl ketone through photooxidation – Part 1: Aging processes of oligomers

Abstract

Abstract. It has recently been established that unsaturated water-soluble organic compounds (UWSOCs) might efficiently form oligomers in polluted fogs and wet aerosol particles, even for weakly soluble ones like methyl vinyl ketone (MVK). The atmospheric relevance of these processes is explored by means of multiphase process model studies in a companion paper. In the present study, we investigate the aging of these aqueous-phase MVK oligomers formed via •OH oxidation, as well as their ability to form secondary organic aerosol (SOA) upon water evaporation. The comparison between aqueous-phase composition and aerosol composition after nebulization of the corresponding solutions shows similar trends for oligomer formation and aging. The measurements reveal that oligomer aging leads to the formation of organic diacids. Quantification of the SOA mass formed after nebulization is performed, and the obtained SOA mass yields seem to depend on the spectral irradiance of the light used to initiate the photochemistry. Investigating a large range of initial MVK concentrations (0.2–20 mM), the results show that their •OH oxidation undergoes competition between functionalization and oligomerization that is dependent on the precursor concentration. At high initial MVK concentrations (≥ 2 mM), oligomerization prevails over functionalization, while at lower initial concentrations, oligomerization is not the major process, and functionalization dominates, resulting in small carbonyls, dicarbonyls and monoacids. The atmospheric implications of these processes are discussed.

Carbon isotope‐constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo‐Gangetic Plain

“…However, these isotope effects are much smaller [Kaye, 1992] than what is expected from the kinetic isotope effects associated with chemical reactions (making and breaking of covalent bonds) [Meusinger et al, 2016]. The isotope effects associated with oligomerization reactions involving organic aerosols are rather complex in nature as it depends on both the reaction mechanism and the partitioning between gas and aerosol phase [Gao et al, 2004;Kalberer et al, 2004;Renard et al, 2015;Tan et al, 2012;Thompson et al, 2016]. For example, a condensation reaction mainly leads to a water molecule being eliminated.…”

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

“…For the biogenicinfluenced cloud water samples (A1-A3), CHO compounds compose 51-56 %, by number, of the dissolved organic species identified (Table S5). CHO compounds potentially arising from aqueous reactions were identified by comparison to laboratory studies of the aqueous photooxidation of α-pinene oxidation products (cis-pinonic acid and the surrogate tricarballylic acid) (Aljawhary et al, 2016) and isoprene oxidation products (methyl vinyl ketone and isoprene SOA) (Nguyen et al, 2012a;Renard et al, 2015) (Table 3). CHOS and CHNOS compounds account for 14 and 7-9 %, respectively, of the measured organic compounds in the A1 and A2 samples; lower percentages were observed for sample A3 (Table S5), consistent with the lower sulfate concentration in A3 (Table 1).…”

Oligomer formation in the troposphere: from experimental knowledge to 3-D modeling

“…4) (e.g., Donahue et al, 2009;Valorso et al, 2011). There, M w stands for the mean organic aerosol molar mass (set to 250 g mol −1 based on Robinson et al, 2007), C OA represents the total organic aerosol mass concentration (µg m −3 ) and P vap is the saturation vapor pressure (atm) and considering an ideal mixture. Figure 3 illustrates the gas-particle partition of the three semi-volatile compounds considered in our work for the two distinct situations.…”