Abstract
Abstract. Photochemical processes inside urban plumes in the Northeast of the United States have been studied using a highly detailed chemical model, based upon the Master Chemical Mechanism (MCM). The model results have been compared to measurements of oxygenated VOCs (acetone, methyl ethyl ketone, acetaldehyde, acetic acid and methanol) obtained during several flights of the NOAA WP-3D aircraft, which sampled plumes from the New York City area during the ICARTT campaign in 2004. The agreement between the model and the measurements was within 40–60 % for all species, except acetic acid. The model results have been used to study the formation and photochemical evolution of acetone, methyl ethyl ketone and acetaldehyde. Under the conditions encountered during the ICARTT campaign, acetone is produced from the oxidation of propane (24–28 %) and i-propanol (<15 %) and from a number of products of i-pentane oxidation. Methyl ethyl ketone (MEK) is mostly produced from the oxidation of n-butane (20–30 %) and 3-methylpentane (<40 %). Acetaldehyde is formed from several precursors, mostly small alkenes, >C5 alkanes, propanal and MEK. Ethane and ethanol oxidation account, respectively, for 6–23 % and 5–25 % of acetaldehyde photochemical formation. The results highlight the importance of alkanes for the photochemical production of ketones and the role of hydroperoxides in sustaining their formation far from the emission sources.
Highlights
Oxygenated Volatile Organic Compounds (VOCs) are important products of the photo-oxidation of hydrocarbons and other organic species in the atmosphere
Both the MCM model and the New England Air Quality Study (NEAQS) parameterizations describe the trends in the ICARTT data for the other species reasonably well, they underestimate the formation of acetaldehyde and methyl ethyl ketone (MEK) during the first day
A significant contribution to the photochemical formation of acetaldehyde comes from the reaction of ethanol with OH (Fig. 10). This route accounts for 5 % up to 25 % of acetaldehyde formation, peaking on the second day, and it is mostly related to direct emissions of ethanol (Table 1), since its photochemical production is very slow
Summary
Oxygenated Volatile Organic Compounds (VOCs) are important products of the photo-oxidation of hydrocarbons and other organic species in the atmosphere. Oxygenated VOCs include carbonyls (aldehydes and ketones), alcohols and carboxylic acids It has been known for many years that these classes of compounds are ubiquitous in the atmosphere (Singh et al, 1994, 1995, 2000, 2001, 2004; Colomb et al, 2006; Muller et al, 2006) and may account for a large fraction of the organic carbon in the troposphere, with some studies suggesting that they might be 2 to 5 times more abundant than all the non-methane hydrocarbons combined (Singh et al, 2001, 2004). Parameter acetylene benzene toluene o-xylene m-xylene p-xylene ethylbenzene n-propylbenzene i-propylbenzene 1,2,3-trimethylbenzene 1,2,4-trimethylbenzene 1,3,5-trimethylbenzene 1-ethyl-2-methyl benzene 1-ethyl-3-methyl benzene 1-ethyl-4-methyl benzene styrene dichloromethane chloroform 1,1,1-trichloroethane tetrachloroethene methyl t-butyl ether formaldehyde acetaldehyde propanal n-butanal n-pentanal methanol ethanol i-propanol acetone methyl ethyl ketone dimethyl sulphide temperature pressure
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