The relative importance of competing pathways for the formation of high-molecular-weight peroxides in the ozonolysis of organic aerosol particles

Abstract

Abstract. High-molecular-weight (HMW) organic compounds are an important component of atmospheric particles, although their origins, possibly including in situ formation pathways, remain incompletely understood. This study investigates the formation of HMW organic peroxides through reactions involving stabilized Criegee intermediates (SCI's). The model system is methyl oleate (MO) mixed with dioctyl adipate (DOA) and myristic acid (MA) in submicron aerosol particles, and Criegee intermediates are formed by the ozonolysis of the double bond in methyl oleate. An aerosol flow tube coupled to a quadrupole aerosol mass spectrometer (AMS) is employed to determine the relative importance of different HMW organic peroxides following the ozonolysis of different mixing mole fractions of MO in DOA and MA. Possible peroxide products include secondary ozonides (SOZ's), α-acyloxyalkyl hydroperoxides and α-acyloxyalkyl alkyl peroxides (αAAHP-type compounds), diperoxides, and monoperoxide oligomers. Of these, the AMS data identify two SOZ's as major HMW products in the ozonolysis of pure methyl oleate as well as in an inert matrix of DOA to as low as 0.04 mole fraction MO. In comparison, in mixed particles of MO and MA, αAAHP-type compounds form in high yields for MO mole fractions of 0.5 or less, suggesting that SCI's efficiently attack the carboxylic acid group of myristic acid. The reactions of SCI's with carboxylic acid groups to form αAAHP-type compounds therefore compete with those of SCI's with aldehydes to form SOZ's, provided that both types of functionalities are present at significant concentrations. The results therefore suggest that SCI's in atmospheric particles contribute to the transformation of carboxylic acids and other protic groups into HMW organic peroxides.

Oligomer formation during gas-phase ozonolysis of small alkenes and enol ethers: new evidence for the central role of the Criegee Intermediate as oligomer chain unit

“…Similarly, peroxidic SOA constituents formed by reactions of the stabilized CI, such as secondary ozonides, α-acyloxyalkyl hydroperoxides and α-alkyloxyalkyl hydroperoxides, involve CI that consist of nine, ten or 13 carbon atoms for the ozonolysis of linear alkenes such as oleic acid (Zahardis and Petrucci, 2007), methyl oleate (Mochida et al, 2006), and 1-tetradecene , and of six to ten carbon atoms for cyclic alkenes (Ziemann, 2003) and the monoterpene α-pinene (Tolocka et al, 2006). By their secondary reactions, these stabilized CI often become associated to aldehydes or carboxylic acids of similar sizes, such as nonanoic acid (oleic acid/ozone system, Zahardis and Petrucci, 2007;Zahardis et al, 2006), tridecanal (1-tetradecene ozonolysis, , or pinonaldehyde (α-pinene ozonolysis, Tolocka et al, 2006), leading to large, low-volatile peroxidic compounds consisting of 18 and more carbon atoms.…”

“…Among those products are secondary ozonides, α-acyloxyalkyl hydroperoxides, cyclic geminal diperoxides, peroxyhemiacetals and diacyl peroxides (Zahardis and Petrucci, 2007;Mochida et al, 2006;Reynolds et al, 2006;Tolocka et al, 2006;Zahardis et al, 2006Zahardis et al, , 2005Docherty et al, 2005;Dreyfus et al, 2005;Ziemann, 2003Ziemann, , 2002. Initial unsaturated compounds are either monoterpenes and cyclic alkenes consisting of six to ten carbon atoms (Tolocka et al, 2006;Docherty et al, 2005;Ziemann, 2003Ziemann, , 2002, cholesterol (Dreyfus et al, 2005) or the linear C18 oleic acid and methyl oleate (Zahardis and Petrucci, 2007;Mochida et al, 2006;Reynolds et al, 2006;Zahardis et al, 2006Zahardis et al, , 2005. Formation reactions leading to those highmolecular peroxidic compounds were partly suggested to take place in the liquid phase within the aerosol particles or heterogeneously.…”

A New Aerosol Flow System for Photochemical and Thermal Studies of Tropospheric Aerosols

“…These are typically much smaller in volume with shorter residence/reaction times, often of the order of a few seconds to minutes (Harrison and Collins 1998;Morris et al 2002;Smith et al 2002;Bröske et al 2003;Jang et al 2003;Lee and Kamens 2005;Mochida et al 2006;Tolocka et al 2006;Vlasenko et al 2006). Flow systems are readily disassembled for cleaning and provide access to different reaction times in one experiment via sampling from ports at different locations along the length of the flow tube.…”

The ozonolysis of primary aliphatic amines in fine particles

“…Conversely, DOS and similar high molecular weight esters (i.e. dioctyl adipate) are common constituents in studies of organic particles (Ziemann, 2005;Mochida et al, 2006) that are not a source of SCI and inert to ozone (Mochida et al, 2006); hence, DOS serves as an excellent negative control for comparison to the studies of ozonized mixed particles of amines with OL.…”

“…These mixed particles contained the inert matrix DOS, which like other esters does not undergo ozonolysis or react with SCI (Mochida et al, 2006;Ziemann, 2005). Figure 6 compares the evolution of the 438 m/z amide between the azelaic acid + ODA + DOS and ODA + OL heterogeneous reaction systems, at four ozone concentrations.…”