Oligomerization Reaction of the Criegee Intermediate Leads to Secondary Organic Aerosol Formation in Ethylene Ozonolysis

Abstract

Ethylene ozonolysis was investigated in laboratory experiments using a Teflon bag reactor. A negative ion chemical ionization mass spectrometer (NI-CIMS) using SO2Cl(-) and Cl(-) as reagent ions was used for product analysis. In addition to the expected gas-phase products, such as formic acid and hydroperoxymethyl formate, oligomeric hydroperoxides composed of the Criegee intermediate (CH2OO) as a chain unit were observed. Furthermore, we observed secondary organic aerosol (SOA) formation from the ethylene ozonolysis, and the particle-phase products were also analyzed by NI-CIMS. The CH2OO oligomers were also observed as particle-phase components, suggesting that the oligomeric hydroperoxides formed in the gas phase partition into the particle phase. By adding methanol as a stabilized Criegee intermediate scavenger, both the gas-phase oligomer formation and SOA formation were strongly suppressed. This indicates that CH2OO plays a critical role in the formation of oligomeric hydroperoxides followed by SOA formation in ethylene ozonolysis. A new formation mechanism for the oligomeric hydroperoxides, which includes sequential addition of CH2OO to hydroperoxides, is proposed.

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

“…Accurate mass measurements (Table 2) of selected OLI-D oligomers agree well with the expected elemental composition for these peroxyhemiacetals. Formation of peroxyhemiacetals has also been suggested in SOA from ozonolysis of 1-tetradecene, 69 a-pinene, 16,23 and ethylene, 44 and photooxidation of dodecane 70 and toluene. 71 Fig .…”

“…Given the smaller number of particles that occur in the presence of formic acid, there should be more low MW condensable species available in the gas phase for each particle to grow to larger sizes. Recently, Sakamoto et al 44 observed the gas phase formation of oligomers containing SCI as the chain unit during ethylene ozonolysis and proposed a new oligomer formation mechanism (reaction (R2)) involving sequential addition of SCI to organic hydroperoxides (ROOHs) instead of to RO 2 radicals. The hydroperoxides included 2-hydroxylethyl hydroperoxide (HOCH 2 CH 2 OOH) produced by OH oxidation of ethylene, and formyloxymethyl hydroperoxide (HCOOCH 2 OOH) formed from reaction of formic acid with SCI.…”

“…40,41 Accurate mass measurements suggested that these oligomers have high oxygen content (average O/C = 0.6) and comprise the majority of isoprene/O 3 derived SOA. 40 Recently, theoretical 45,46 and experimental [41][42][43][44] studies have suggested the gas phase formation of low-volatility oligomers containing SCI as the repeat unit during the ozonolysis of small enol ethers and alkenes (including isoprene) in dry air. Two different mechanisms have been proposed: sequential addition of SCI to peroxy radicals (RO 2 ) (reaction (R1)), 43 or to hydroperoxides (ROOH) (reaction (R2)).…”

“…Two different mechanisms have been proposed: sequential addition of SCI to peroxy radicals (RO 2 ) (reaction (R1)), 43 or to hydroperoxides (ROOH) (reaction (R2)). 44 Sadezky et al 43 investigated the formation of oligomers from the ozonolysis of a number of simple alkenes including trans-3-hexene in a static chamber, and proposed the structures and mechanisms shown in reaction (R1). We report here an expanded investigation of the ozonolysis of trans-3-hexene in which particle composition is probed as a function of size.…”

Reactions between Criegee Intermediates and the Inorganic Acids HCl and HNO3: Kinetics and Atmospheric Implications

“…[1,2] They are thought to have a significant influence on the oxidative capacity of the atmosphere and, through reaction with trace species, to contribute to new particle formation. [3][4][5][6][7][8][9] Unimolecular dissociation of vibrationally hot nascent CIs is a major source of night-time OH in the troposphere. [3,10] Stabilized CIs react quickly (~10 -12 -10 -10 cm 3 s -1 ) with many trace atmospheric gases.…”