Friday, October 25, 2013

Collection Of Acid Precipitation

Wet deposition samples can be measured to determine chemical concentrations in almost any area. The National Atmospheric Deposition Program (NADP) at the Illinois State Water Survey, University of Illinois, maintains three networks with more than 350 deposition monitoring sites. The NADP National Trends Network has 250 sites in the U.S. located far from the point sources of pollution. Each site has an automated precipitation collector and gauge to gather samples only during rain or snowfall.

Weekly samples are collected and sent to the NADP for analysis. The network measures acidity and calcium, magnesium, sodium, potassium, sulfate, nitrate, chloride, and ammonium ions.

NADP monitoring data show that wet sulphate deposition has decreased an average of 30 percent since the early 1990s in the eastern United States. The largest decreases occurred in Maryland, New York, Virginia, West Virginia, and Pennsylvania. Nitrogen deposition has decreased as well, but to a lesser extent.

Legislative mandates, federal government programs, and environmental-friendly changes in fossil fuel use in electrical power plants have successfully lowered the emission of SO2 and NOx and the resulting acid deposition in the U.S. since the 1980s. However, the problem still exists. Scientists continue to try to fully understand acid rain and its long-term effects on the environment and on human health.

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