Ozone variation with height in a forest canopy—results from a passive sampling field campaign

Vertical ozone profiles were measured using a 10.5 m tower in a low (13 m) forest canopy in the Lower Fraser Valley, British Columbia, Canada. Ozone was measured cumulatively using passive samplers over five 2-week periods, at seven canopy heights. A strong power-law relationship was found between biweekly mean hourly ozone concentration and within-canopy height (r2=0.98–0.99), with a 31–47% reduction in ozone towards the forest floor. Using a Buckingham-Pi dimensional analysis the plots were normalised. Through similarity theory the equation y=1.03x0.15b was derived for ozone concentration with canopy height; where y is normalised biweekly mean hourly ozone, x is height normalised by the height of the canopy, and b is a stability parameter that increases with increased stability. This study presents a unique method of measuring within-canopy ozone that is inexpensive, yields good results, and may be further developed for flux estimation.