Analyses of ozone observations obtained at single surface stations usually indicate an afternoon peaking diurnal variation in ozone concentration; several photochemical models have been developed which can accurately predict this trend by adjusting the rate constants of reaction or the concentration of the several precursor gases to ozone. Ozone observations obtained atop isolated hills in rural surroundings rarely show such an afternoon peaking diurnal variation of concentrations; the behavior of ozone concentrations at these sites can be predicted by meteorological analysis, based on the classical hypothesis of a single ozone source in the stratosphere, and subsident transport to the measuring station. Observations at Whiteface Mountain and surrounding surface sites with supporting meteorological analyses show that it is impossible to define variation in ozone concentrations uniquely by either of these analytical techniques. These observations do strongly support an hypothesis that above average ozone concentrations over this area have their source above the 850-mbar level.