A fast response chemiluminescent ozone sensor was mounted in National Center for Atmospheric Research Queen Air aircraft instrument for air motion, temperature, and humidity measurements. The vertical flux of ozone was then obtained by the eddy correlation technique for several flights of the daytime atmospheric boudnary layer over eastern Colorado. Because of the range and mobility of the aircraft, this technique can be utilized for a wide variety of situations. For example, a flight leg over an interstate highway shows large negative fluctuations in O3 due to vehicular emission of NO that are well correlated with positive temperature and vertical velocity fluctuations. On one flight the significant terms in the mean ozone concentration budget (and also, for comparison, the sensible heat and humidity budgets) were evaluated from the airplane measurements. For this flight, which occurred under clear skies over range and cropland about 100 km northeast of Denver, the time rate of change of ozone density in the lower half of the boundary layer was about 2.4 ng m-3 s-1. This was several times larger than the contributions by horizontal advection and the divergence of the vertical eddy flux of ozone. Thus, most of the observed increase in ozone concentration must have been the result of internal photochemical production of ozone. This may be the first well-documented example where the rate of O3 increase with time is shown to be balanced by photochemical production of O3. The deposition velocity of ozone for this case was about 0.47 cm s-1.