The impact of natural non-methane hydrocarbon oxidation on the free radical and ozone budgets above a eucalyptus forest

Abstract

The impact of the oxidation of natural non-methane hydrocarbon, particularly of isoprene, on the free radical formation and on ozone budgets has been evaluated on the basis of the results of the FIELDVOC'94 campaign. Four reduced chemical mechanisms for hydrocarbon oxidation and a detailed chemical scheme for C₁–C₅ hydrocarbon oxidation incorporated into a box model suitable for the integration of stiff chemical reactions have been used for this study. The observed peroxy radical concentrations are well simulated by the models. Hydroperoxy radicals contribute by about 40–60% to the daytime peak of peroxy radicals. Terpenes and isoprene chemistry could account for about 10% and 45% of the observed levels of daytime peroxy radical concentrations. Ozone reactions contribute up to 50% to the organic peroxy radicals produced at night by isoprene oxidation. Isoprene chemistry reduces by a factor of two to three the computed radical concentrations and contributes by about 50–100% to the net ozone daytime photochemical production in this forested area.