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Depletion of the stratospheric ozone layer could result in increasing u.v. radiation at ground level. Increasing concentrations of greenhouse gases could result in increasing temperature. The response of boundary layer chemistry on increases in energy, in the form of increasing surface temperature or increasing u.v. radiation, will be an increased photochemical reactivity. In this paper we present the results of a model study on the sensitivity of episodic and long-term averaged ozone and oxidant (Ox, sum of O3 and NO2) concentrations on changes in temperature and u.v. radiation. Ground level ozone and oxidant concentrations are calculated for summer 1989 by means of a Lagrangian long-range transport model for a receptor point in the central part of The Netherlands. For a 10% decrease in ozone column density and a 10% increase in surface temperature (on average ?t = 1.6°C) the increase in O3 and Ox 98 percentile value is about 2.7%. The additional ozone production will increase the number of exceedences of threshold values; this may lead to greater human exposures during episodes. The calculations for the reference emission situation resulted for the period 1 May-1 October 1989 (total 3672 h) in 56 observations of 1-h averaged O3 concentrations which exceed the level of 75 ppb; in one case the O3 concentration exceeds 100 ppb. In the sensitivity calculations with increased temperature and reduced ozone column these numbers increase to 72 h (+29%) and 6 h (+600%), respectively. A possible increase in natural VOC emissions from forests due to a global warming may further enhance the number of exceedences.