Vertical gradients of ozone and carbon dioxide within a deciduous forest in Central Pennsylvania

Ambient concentrations of ozone (O 3) and carbon dioxide (CO 2) were measured at locations from the forest floor to the top of the canopy in a deciduous forest at the Moshannon State Forest in northcentral Pennsylvania. O 3 concentrations were measured from May–September for three years (1993–1995) while CO 2 concentrations were measured only during July and August of 1994. O 3 concentrations increased steadily during the day at all locations, peaking during the middle to late afternoon hours. O 3 concentrations then steadily declined to their lowest point, just before dawn. Vertical O 3 concentration gradients varied seasonally and among years. However, O 3 concentrations were highest within the forest canopy and lowest at the forest floor, with an average difference of approximately 13%. Differences in O 3 concentrations between the canopy and forest floor were greatest at night. O 3 concentrations were slightly higher at locations within the canopy than above the canopy. CO 2 concentrations were consistenly higher near the forest floor and were higher above the canopy than within the canopy. CO 2 concentrations were higher at night than during the day at all locations, especially near the forest floor.