National Atmospheric Deposition Program.

Two NADP sites, located at 2524 m elevation in upper montane forest (Sugarloaf = CO94) and 3525 m in elevation and in alpine tundra (Niwot Ridge Saddle = CO02), collected precipitation samples on a weekly basis. These were analyzed for pH, conductivity, anions (Cl-, SO4--, NO3-), and cations (Ca++, Mg++, K+, Na+, NH4+, H+) at the Central Analytical Laboratory in Champaign, IL