Atmospheric Oxidation of Vinyl Ethers

Recent field campaign and modeling studies have highlighted significant discrepancies between expected levels of pollutants from solvent use using current emission inventories and observed levels. This indicates either inadequate emission inventory calculations and/or knowledge of the atmospheric fate of emitted compounds, of which mostly significant fraction is composed of oxygenated organic compounds such as ethers. Vinyl ethers are widely applied in industry as oxygenated solvents, additives and in different types of coatings. They are released to the atmosphere entirely from anthropogenic sources. Consequently, a better understanding of the atmospheric fate of vinyl ethers is highly desirable. This work presents investigations on the gas-phase chemistry of vinyl ethers performed in a 405 l borosilicate glass chamber and a 1080 l quartz glass reactor in the Bergische University Wuppertal, Germany. Relative rate coefficients were determined for the OH radical, ozone and NO3 radical initiated oxidation of selected vinyl ethers. Using in situ Fourier transform infrared (FTIR) absorption spectroscopy the following rate coefficients were obtained at room temperature and atmospheric pressure in synthetic air (in cm3 molecule-1 s-1): Vinyl ether kOH×1011 kO3×1016 kNO3×1012 Propyl vinyl ether, n-C3H7OCH=CH2 9.73±1.94 2.34±0.48 1.85±0.53 Butyl vinyl ether n-C4H9OCH=CH2 11.3±3.1 2.59±0.52 2.10±0.54 Ethyleneglycol monovinyl ether HOCH2CH2OCH=CH2 10.4±2.15 2.02±0.41 1.95±0.50 Ethyleneglycol divinyl ether H2C=CHOCH2CH2OCH=CH2 12.3±3.25 1.69±0.41 2.23±0.46 Diethyleneglycol divinyl ether H2C=CHOCH2CH2OCH2CH2OCH=CH2 14.2±3.00 2.70±0.56 6.14±1.38 Product investigations on the gas-phase reactions of the OH radical, ozone and NO3 radical with propyl vinyl ether (PVE) and butyl vinyl ether (BVE) were performed in the 405 l borosilicate glass chamber by in situ FTIR spectroscopy. At room temperature and atmospheric pressure of synthetic air the products observed and their molar formation yields were as follows: Reactans Products Formate (%) HCHO (%) HPMFa (%) CO (%) FAb (%) OH Propyl vinyl ether, n-C3H7OCH=CH2 78.6±8.8i) 63.0±9.0ii) 75.9±8.4i) 61.3±6.3ii) - - - Butyl vinyl ether n-C4H9OCH=CH2 64.7±7.1i) 52.2±6.3ii) 64.3±6.9i) 52.9±6.3ii) - - - O3 Propyl vinyl ether, n-C3H7OCH=CH2 88.3±9.3iii) 89.7±9.9iv) - 12.9±4.0iv) - 13.0±3.4iv) - 10.9±2.6iv) - 1.94±0.59iv) Butyl vinyl ether n-C4H9OCH=CH2 78.5±8.8iii) 76.7±8.9iv) - 10.5±1.8iv) - 12.0±2.9iv) - 8.2±1.3iv) - 2.6±0.54iv) NO3 Propyl vinyl ether, n-C3H7OCH=CH2 52.7±5.9 55.0±6.3 - - - Butyl vinyl ether n-C4H9OCH=CH2 43.6±4.5 48.0±5.6 - - - i) with NOx present; ii) without NOx present; iii) with cyclohexane as OH radical scavenger; iv) with 1,3,5-trimethylbenzene as OH radial tracer a) HPMF---hydroperoxy methyl formate; b) FA---formic anhydride Hydroxyl radical yields of (17±9)% and (18±9)% have been estimated for the reactions of PVE and BVE with ozone, respectively. Total nitrate formation yields of (56.0±12.3)% and (57.1±12.3)% have been estimated for the NO3 radical initiated oxidation of PVE and BVE, respectively. Simplified reaction mechanisms for the reactions of the OH radical, ozone and NO3 radical with the investigated vinyl ethers are proposed. Secondary organic aerosol (SOA) formation was observed in the reactions of ozone with PVE and BVE. The observed aerosol profiles showed typical behavior associated with homogeneous nucleation. In the presence of an excess of cyclohexane to scavenge OH, SOA yields of 0.4% were obtained for PVE and 0.3-1.1% for BVE. The role that the OH radial scavenger might play in the SOA formation is unclear. This work has augmented the atmospheric chemistry database for vinyl ethers; it has substantially improved the knowledge on the distribution of oxidation products formed in the atmospheric degradation of vinyl ethers. All the information will allow a better assessment of the potential environmental impacts of vinyl ethers.