Local concentrations of the tropospheric oxidants OH and O-3; Measurement and interpretation

Measurements of the oxidants OH and O, have been carried out at the Weybourne Atmospheric Observatory (WAO) in North Norfolk. These measurements are compared with model calculations and as an example one day (June 22nd, 1995) is presented. The comparison for OH shows good agreement, indicating that the applied model sufficiently describes the relevant tropospheric chemistry and that the measurement of the ancillary data provides a set which contains all the necessary information. The model further allows us to specify the contribution from the source and sink terms to the measured concentration, showing, e.g. that the observed strong decrease of the OH in the afternoon is mainly a result of changes in the source term and that, in the morning, the reaction with NO, is the main sink. For the observed ozone concentration a detailed calculation was made to estimate the influence of transport on the measured concentration indicating that transport contributes ca. 40% to the total sink term, and that sometimes much larger contributions are possible. The calculated net flux shows strong influences from the chemical composition of the transported air masses as well as from the strength of the transport.