Wet Deposition Monitoring (including Mercury)
Atmospheric deposition is the process by which airborne pollutants are deposited to the earth. These pollutants include, but are not limited to, sulfur dioxide, nitrogen oxides, ammonia, and mercury. Total deposition consists of both wet and dry components.
Wet deposition occurs when pollutants are deposited in combination with precipitation, predominantly by rain and snow, but also by clouds and fog. The NPS monitors wet deposition through the National Atmospheric Deposition Program (NADP).
The NADP National Trends Network (NTN) collects weekly precipitation samples that are analyzed by a central analytical laboratory at the Illinois State Water Survey for pH, conductivity, cations (hydrogen, calcium, sodium, magnesium, potassium, and ammonium) and anions (sulfate, nitrate, and chloride). Each site includes a precipitation collector and a rain gage.
The NADP Mercury Deposition Network (MDN) also collects weekly precipitation samples. These samples are analyzed by Frontier Geosciences for mercury. MDN sites include a modified precipitation collector and a rain gauge.
Data for both networks is available on the NADP web site.
|Metadata||what, where, and when monitors have operated in national parks||Monitoring History Database|
|Wet Deposition||ph and conductivity: sulfate, nitrate, chloride, calcium, magnesium, sodium, potassium, and ammonium concentration and deposition; and precipitation amount||NADP NTN web site|
|Wet Mercury Deposition||mercury concentration and deposition, and precipitation amount||NADP MDN web site|
|NADP Annual Isopleth Maps||annual isopleth maps of constituent concentration or wet deposition||NADP NTN web site/isopleths|
|CASTNet Total Deposition Charts||summary charts of total sulfur and nitrogen deposition||
CASTNet web site/siteinfo
*charts are found by clicking on a site under Site Information
Atmospheric deposition in the U.S. has changed significantly over the past two decades. Sulfate deposition has notably declined in the East since 1988, largely due to Title IV of the Clean Air Act which required SO2 emission reductions from power plants. Nitrate deposition has also declined in the Northeast, due to another regulatory program that reduced NOx emissions in the Northeast from motor vehicles.
Ammonium deposition, however, has increased across the U.S. Deposition of ammonium is highest through the Midwest and over the Great Plains region, the result of high ammonia emissions associated with agricultural activities, such as fertilizer use and livestock production.
|NPS Deposition Program Manager||Kristi Morris||(303) 987-6941|