LACTOZ: Chemical Processes related to Tropospheric Ozone

Summary

The LACTOZ project has provided an extended kinetic and mechanistic data base that gives much improved quantitative description of the chemical production and loss of ozone from its precursor molecules — nitrogen oxides (NO_x) and volatile organic compounds (VOCs) — in the atmospheric boundary layer and free troposphere. The data base relates to the following classes of reactions:

• * reactions of hydroxyl radicals with VOCs: this determines the rates of reaction of VOCs in the sunlit atmosphere:

• * reactions of nitrate radicals with VOCs and peroxy radicals and of ozone with alkenes: this controls the non photochemical homogeneous oxidation of VOCs:

• * reactions of peroxy radicals (self reactions, reaction with HO₂ other RO₂, NO and NO₂), central to the main ozone generation process:

• * reactivity of nitrates and peroxynitrates, which is central to the atmospheric transport of NO_x.

Improved or new photolysis parameters of photo-labile species (e.g. carbonyl compounds) have been provided, and significantly new mechanistic information has been established for the oxidation of aromatic and biogenic VOCs (especially isoprene). The available data base has been used to establish structure-reactivity relationships to be used for predicting the reactivity of the very large number of VOCs involved in the generation of tropospheric ozone. As an application of LACTOZ, the data have been incorporated into many atmospheric models describing and predicting ozone and photo-oxidant formation.