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Author(s):   Orlando, J.J.; Tyndall, G.S.
Title:   Mechanisms for the reactions of OH with two unsaturated aldehydes: Crotonaldehyde and acrolein
Journal:   J. Phys. Chem. A
Volume:   106
Page(s):   12252 - 12259
Year:   2002
Reference type:   Journal article
Squib:   2002ORL/TYN12252-12259

Reaction:   Methacrolein + ·OH → Products
Reaction order:   2
Pressure:  0.93 - 0.96 bar
Rate expression:   2.8x10-11 [cm3/molecule s]
Bath gas:   air
Category:  Experiment
Data type:   Absolute value measured directly
Experimental procedure:   Static or low flow - Data taken vs time
Excitation technique:   Direct photolysis
Time resolution:   By end product analysis
Analytical technique:   Fourier transform (FTIR)
Comments:   Experiments were performed at the room tem[perature.


The mechanisms for the reaction of OH with the unsaturated aldehydes, acrolein and crotonaldehyde, have been determined at 1 atm total pressure in the presence of NOx using an environmental chamber/FTIR spectrometer system. Products observed in the OH-initiated oxidation of acrolein were CO, CO2, CH2O, HOCH2CHO (glycolaldehyde), and HCOOH, while the major products identified in the OH-initiated oxidation of crotonaldehyde were CO, CO2, CH3CHO, and HC(O)CHO (glyoxal). Also observed were two PANtype species, identified as CH2dCH-C(O)O2NO2 (APAN) from acrolein oxidation and CH3-CHdCHC(O)O2NO2 (CPAN) from crotonaldehyde. The near-complete mass balance obtained in these experiments allows for a quantitative assessment of the branching ratios for abstraction and addition in these reactions. It is shown that about 68% (50%) of the OH reaction with acrolein (crotonaldehyde) proceeds via abstraction of the aldehydic H, with the remainder occurring via addition to the double bond. The data allow for a more accurate assessment of the atmospheric source strength of APAN, a species which has now been identified in ambient air. Trends in the reactivity of acrolein and its methylated derivatives, methacrolein and crotonaldehyde, are also discussed; data are shown to be consistent with structure-reactivity considerations.

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