Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers A. Sadezky1,2, P. Chaimbault3, A. Mellouki2, A. Römpp1, R. Winterhalter1, G. Le Bras2, and G. K. Moortgat1 1Max-Planck-Institute for Chemistry, Atmospheric Chemistry Department, P.O. Box 3060, 55020 Mainz, Germany 2Laboratoire de Combustion et de Systèmes Réactifs, CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France 3Institut de Chimie Organique et Analytique, UMR 6005, BP 6759, University of Orléans, 45067 Orléans Cedex 2, France
Abstract. Formation of secondary organic aerosol has been observed in the gas phase
ozonolysis of a series of enol ethers, among them several alkyl vinyl ethers
(AVE, ROCH=CH2), such as ethyl, propyl, n-butyl, iso-butyl, t-butyl vinyl
ether, and ethyl propenyl ether (EPE, C2H5OCH=CHCH3). The
ozonolysis has been studied in a 570 l spherical glass reactor at
ambient pressure (730 Torr) and room temperature (296 K). Gas phase reaction
products were investigated by in-situ FTIR spectroscopy, and secondary
organic aerosol (SOA) formation was monitored by a scanning mobility
particle sizer (SMPS). The chemical composition of the formed SOA was
analysed by a hybrid mass spectrometer using electrospray ionization (ESI).
The main stable gas phase reaction product is the respective alkyl formate
ROC(O)H, formed with yields of 60 to 80%, implying that similar yields
of the corresponding excited Criegee Intermediates (CI) CH2O2 for the
and CH3CHO2 for EPE are generated. Measured SOA yields are between
2 to 4% for all enol ethers. Furthermore, SOA formation is strongly
reduced or suppressed by the presence of an excess of formic acid, which
acts as an efficient CI scavenger.
Chemical analysis of the formed SOA by ESI(+)/MS-TOF allows to identify
oligomeric compounds in the mass range 200 to 800 u as its major
constituents. Repetitive chain units are identified as CH2O2 (mass
46) for the AVE and C2H4O2 (mass 60) for EPE and thus have
the same chemical compositions as the respective major Criegee Intermediates
formed during ozonolysis of these ethers. The oligomeric structure and chain
unit identity are confirmed by HPLC/ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF
experiments, whereby successive and systematic loss of a fragment with mass
46 for the AVE (and mass 60 for EPE) is observed. It is proposed
that the oligomer has the following basic structure of an oligoperoxide,
-[CH(R)-O-O]n-, where R=H for the AVE and R=CH3 for the EPE.
Oligoperoxide formation is thus suggested to be another, so far unknown
reaction of stabilized Criegee Intermediates in the gas phase ozonolysis of
oxygen-containing alkenes leading to SOA formation.
Citation: Sadezky, A., Chaimbault, P., Mellouki, A., Römpp, A., Winterhalter, R., Le Bras, G., and Moortgat, G. K.: Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers, Atmos. Chem. Phys., 6, 5009-5024, doi:10.5194/acp-6-5009-2006, 2006.