Question

What are the sources (source chemical reactions including species in the reactions)

of: (i.) OH         and              (ii.)   Peroxy Radical CH3OO           in the troposphere ?

Answer 1

The basic ingredients for the formation of hydroxyl are NO and NO₂, water vapor, ozone and radiation at wavelengths shorter than 315 nm. The NO₂ is very reactive and may form O₃, which in turn may yield hydroxyl.

The main source of hydroxyl radicals in the troposphere is the photolysis of ozone by ultraviolet light, in the presence of water vapour ,

O₃ + hv == > O(¹D) + O₂

O(¹D) react with H₂O to form the hydroxyl radical HO

O(¹D) + H₂O === > HO + HO

The hydroxyl radical is often referred to as the "detergent" of the troposphere because it reacts with many pollutants, decomposing them through "cracking", often acting as the first step to their removal. It also has an important role in eliminating some greenhouse gases like methane and ozone. It is a short lived free radical

The species RO₂ represents a variety of complex organic peroxy radicals. These reactions occur during the photooxidation of CO, CH₄ and hydrocarbons.

Peroxy radicals RO₂ (where R is an alkyl) are very much intertwined with hydroxyl in the oxidation cycle. They are not as efficient as hydroxyl, but react with themselves to form H₂O₂, an important oxidant in cloud droplets.