Prediction of the abiotic degradability of organic compounds in the troposphere

A statistically relevant correlation between the reaction rate coefficient, k_OH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies E_i,v, reveals two classes of compounds: aromatics where –log(k_OH/cm³s^-1)3/2E_i,v(eV)–2 and aliphatics where –log(k_OH/cm³s^-1)4/5E_i,v(eV)+3. The prediction of the rate coefficient, k_OH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×10⁵ cm³, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated.