The Reaction of Acetyl Peroxy Radical with Aldehyde: Impact on the OH Radical Model Simulation

Abstract:

Understanding the budget of OH (hydroxyl radical) is very important for investigating the atmospheric oxidation capacity, aerosol formation and climate change. Recent studies indicate that there may be a great gap between the modeled and measured OH concentrations in some rural forest areas. This gap may result from our incomplete knowledge about the oxidation mechanism of volatile organic compounds (VOCs). Here, we suggest that acetyl peroxy radical (CH₃C(O)OO∙), the OH-initiated oxidation intermediate of most VOCs, can take the H-atom from the aldehyde group to form corresponding peroxy carboxylic acids. This reaction has not been concerned in the atmosphere. The acetyl peroxy radical may share the “oxidation responsibility” of OH, and help saving OH from being consumed by aldehyde. Using a box model coupled with the isoprene-OH reaction mechanism selected from MCM v3.2, we get OH saving ratio (SR_OH) when we compare the modeled OH levels in the presence and absence of the reaction of acetyl peroxy radical with aldehyde. We find that SR_OH is not a constant but a function of OH production rate, reaction time, isoprene concentration and the ratio of aldehyde to isoprene. It is expected that CH₃C(O)OO∙ radical, a non-OH oxidant, plays an important role in maintaining the oxidation capacity of the troposphere.