OZONE CONCENTRATION CHARACTERISTICS AT A HIGH-ELEVATION FOREST SITE

Atmospheric ozone concentrations have been monitored at a subalpine fo rest ecosystem site, 3180 m above mean sea level (msl), and at a 2680 m msl forest-steppe ecotone site 15 km to the southeast. Ozone concent rations were monitored at three heights above the ground on a 30 m tow er al the higher elevation site, and on a 10 m tower in a large meadow downwind of this site. The research reported here concentrates on the data for the first six months of 1990-1994. The diel amplitude of ozo ne concentrations is very small in winter, increasing as the seasons a dvance to June. Following snowmelt in late May or June. the nighttime minima decrease under the forest canopy. The highest monthly mean ozon e concentrations occur in April or May, depending on the year. Episoda l high concentrations were recorded during spring months when upper le vel atmospheric low pressure troughs and cut-off low centers occurred. These contributions peak in May, and add about 10% to normal May back ground ozone concentrations. varying widely from year to year. Spectra l representations of ozone concentrations, illustrate the suppression of the diel peak during spring months, when stratospheric-tropospheric intrusion patterns show no significant diel cycle.