Largely in response to the need for "acid rain” information in 1978, State Agricultural Experiment Stations in the north-central United States formed the National Atmospheric Deposition Program or NADP (http://nadp.sws.uiuc.edu/). From its beginning, the NADP focused on measuring the chemistry of precipitation and the deposition of chemicals from the atmosphere. The Illinois State Water Survey (ISWS) was selected as the first and only NADP Central Analytical Laboratory (CAL).

            A 22-station network began collecting precipitation samples for chemical analysis in late 1978, and this network grew rapidly to a nationwide network of nearly 200 stations by the mid-1980s. As the network grew, so, too, did the reputation of the ISWS for producing high-quality measurements of hydrogen (acidity as pH), sulfate, nitrate, ammonium, chloride, and base cations (such as calcium, magnesium, potassium, and sodium).

            Twenty-five years later, the ISWS continues to serve as the NADP CAL and has achieved international recognition for its expertise in measuring acidic compounds, nutrients, and base cations in precipitation. In 1997, the NADP Executive Committee chose the ISWS to coordinate the entire program, which now encompasses the National Trends Network of 250 stations, a Mercury Deposition Network of nearly 75 stations, and more than 150 cooperators from federal, state, local, and tribal agencies; universities; and the private and public sectors.