Ozone concentrations above a Douglas-fir forest canopy in western Washington U.S.A.

Abstract

Ozone concentrations were monitored above a 30 m Douglas-fir canopy at Cedar River, Washington from 1 April to 30 September in 1986 and 1987. Maximum average hourly ozone concentrations were similar in both years. Ozone concentrations exceeded 0.12 ppm on 2 days in 1986 and 1 day in 1987. Fifteen and 14 days had ozone concentrations greater than or equal to 0.08 ppm in 1986 and 1987, respectively. Ozone concentrations were positively related to daily radiation and maximum daily air temperature. However, only 46 per cent of the variance in ozone concentration in 1986 could be explained by solar radiation and even less was explained by maximum temperature (26%). In 1987, 51 and 54 per cent of the variation in ozone concentration was explained by solar radiation and temperature, respectively. Maximum average hourly ozone concentrations peaked near 1500 h (Pacific Standard Time) for days > 0.06 ppm with minimum values near 0600 h. Highest concentrations were observed when the wind was blowing from the northwest from the Seattle area indicating that photochemical oxidation of NO_x was a major source of elevated ozone. If the data represent current levels of ozone some potential for forest damage exists in Puget Sound forests.