Assessment of atmospheric exposure and deposition to high-elevation forests in the eastern United States

The report summarizes the results of the four year field measurement and data analysis program of MCCP. The MCCP is sponsored by the U.S. Environmental Protection Agency as part of the joint U.S. Forest Service-EPA Spruce-Fir Research Cooperative. The objectives of the project have been met and the result is an assessment of principal atmospheric constituents as they impact the high elevation forests of the Eastern U.S. Deposition of SO4(-2), NO3(-), H(+), and NH(4+) in cloud water represents a significant input to forest canopies with elevations greater than 1000m. Cloud water deposition can exceed wet (rain) deposition and may be the dominant process for input of sulfate and nitrate compounds during the growing season in high elevation forests frequently exposed to clouds. Cloud water pH concentrations may be as much as 0.6pH units lower than pH in rain. SO(4+) and NO3(-) concentrations are also higher in cloud water than in precipitation. Ozone data reveals that significant differences exist between ozone concentrations at high elevation and low elevation sites. The primary effect of the difference is to produce higher mean ozone concentrations and longer episodes at the higher elevation sites.