No abstract

A fast response chemiluminescent ozone sensor was mounted in a National Center for Atmospheric Research Queen Air aircraft instrumented for air motion, temperature, and humidity measurements. The vertical flux of ozone was then obtained by the eddy correlation technique for several flights in the day‐time atmospheric boundary 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.

In an effort to describe the basic vertical structure of the nocturnal boundary layer, observations from four experiments are analyzed. During the night, the depth of significant cooling appears to increase with time while the depth of the turbulence and height of the low level wind maximum tend to remain constant or decrease with time. Since the inversion layer extends above the low level wind maximum and shear is small in the region of the low level jet, the Richardson number reaches a maximum at the jet level and then decreases again with height. As a result, turbulence is observed to be a minimum at the height of the low level wind maximum and then increases again above this height.

Ozone flux has been measured from aircraft by the eddy correlation technique over the Gulf of Mexico, the north Pacific Ocean, and a Gulf Coast pine forest. Measurements over the Gulf were obtained in polluted air (which had flowed down the Mississippi valley) over relatively warm water, while the north Pacific observations were obtained in pristine air over relatively cold water with nearly neutral stratification. Values of the surface resistance to ozone were about 1.8×103 s m−1 over both ocean surfaces and 50 s m−1 over the forest, with an accuracy of better than ±15%. Photochemical production of ozone during midmorning with clear skies over the Gulf of Mexico was 0.2–0.3 ng m−3 s−1, which is an order of magnitude less than that observed over northeastern Colorado.

We present airplane measurements of the stably strattied nocturnal boundary layer obtained during the Severe Environmental Storms and Mesoscale Experiment (SESAME) in 1979. The cases presented here were obtained over rolling terrain in central Oklahama, with a mean slope of about 0.003. The results are in general agreement with previous modeling and observational studies for the mean and turbulence structure of the nocturnal boundary layer, with the exception that the eddy diffusivity of heat, and consequently the flux Richardson number are less than expected.