Atmospheric Deposition

Atmospheric deposition is the process, long recognized by scientists, whereby precipitation (rain, snow, and fog), particles, aerosols, and gases move from the atmosphere to the earth’s surface. There are several different forms of atmospheric deposition but the most widely acknowledged form is acidic. Acidic deposition hugely effects lakes, streams, and forests.

Materials reaching the earth in precipitation or as dry deposition originate from a variety of air pollution sources and can be harmful to the environment and public health. Acidic deposition is the most widely acknowledged form of atmospheric deposition, with well-known effects on lakes, streams, and forests. More recently, atmospheric contributions of nutrients have received increasing attention, particularly as a source of excessive nitrogen entering the Chesapeake Bay. In addition, atmospheric deposition may be a significant source of environmental contaminants such as trace metals and toxic organic compounds.

Results of the National Atmospheric Deposition Program/National Trends Network indicate that Maryland is in or near the region of most acidic precipitation and receives some of the highest concentrations of sulfate and nitrate deposition in the United States. Sulfate and nitrate are the primary contributors to acidic deposition. In 1987, Maryland’s Synoptic Stream Chemistry Survey concluded that approximately one-third of all headwater streams in Maryland are sensitive to acidification with ANC less than 200 µeq/l) or are already acidic (ANC less than 0 µeq/l) as a result of atmospheric deposition. The MSSCS estimated that most of the acidic or acid-sensitive streams in Maryland are located in the southern Coastal Plain (74% of streams in the region) and the Appalachian Plateau (52%).