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USGS - science for a changing world


Acid Rain, Atmospheric Deposition and Precipitation Chemistry

picture of twirling vines in rain forest picture of water on rust dripping down picture of bluish abstract reflection in water picture of rain dripping in shallow water with granite bottom picture of CO13


Trends in precipitation chemistry across the U.S. 1985–2017: Quantifying the benefits from 30 years of Clean Air Act amendment regulation (2021)

This study reports trends in wet-precipitation chemistry in response to emissions reductions implemented as part of the CAA.
Trends were calculated for sulfate (SO4), nitrate (NO3) and ammonium (NH4) from 1985 to 2017 at 168 stations
operated by the National Atmospheric Deposition Program (NADP); stations were divided into 9 regions across
the United States. Trend analyses were conducted for three time periods: Period 1 (1985–1999), Period 2
(2000–2017), and the entire study period (1985–2017). Seasonal and regional Kendall trend analyses reveal
significant decreasing trends in mean wet-precipitation SO4 concentrations in all 9 regions during the entire
study period. The journal article is available here: McHale et al., 2021

Atmospheric mercury deposition to forests in the eastern USA (May 2017)

Atmospheric mercury (Hg) deposition to forests is important because half of the land cover in the eastern USA is forest. Mercury was measured in autumn litterfall and weekly precipitation samples at a total of 27 National Atmospheric Deposition Program (NADP) monitoring sites in deciduous and mixed deciduous-coniferous forests in 16 states in the eastern USA during 2007-2014. The journal article is available at:

The USGS has Introduced Satellite Telemetry at 11 NADP National Trends Sites as a Pilot Study (Nov. 2016)

Current precipitation data for participating sites can now be accessed on the USGS RealTime site:

Soil acidification from acid rain that is harmful to plant and aquatic life has now begun to reverse in forests of the northeastern United States and eastern Canada (Oct. 2015)

Reduced acid rain levels resulting from American and Canadian air-pollution control measures have begun to reverse soil acidification across this broad region," said Gregory Lawrence, a USGS soil and water chemist and lead study author. "The start of widespread soil recovery is a key step to remedy the long legacy of acid rain impacts on terrestrial and aquatic ecosystems," according to Lawrence. The study is available at:

Estimates of Inorganic Nitrogen Wet Deposition from Precipitation for the Conterminous United States, 1955-84 (2014)

This U.S. Geological report provides estimates of inorganic nitrogen deposition from precipitation for the conterminous United States for 1955-56, 1961-65, and 1981-84, preceding the inception of the NADP. A copy of this report and data sets are available at:

USGS Measures Fallout from Fukushima in U.S. NADP Precipitation Samples (2012)

USGS and the National Atmospheric Deposition Program (NADP) networks measured fission-product isotopes in the U.S. from the Fukushima Dai-ichi nuclear power facility atmospheric release incidents, which occurred March 12 and 14, 2011 near Sendai, Japan.  This project added to the body of knowledge about radioactive fallout from the March 12-14, 2011 incident and exhibited the capabilities of the USGS and NADP to respond to an unexpected atmospheric release. Details and publications on the results are now available at


The U.S. Geological Survey (USGS) is the lead federal agency for the monitoring of wet atmospheric deposition (chemical constituents deposited from the atmosphere via rain, sleet, and snow) in the United States. The USGS atmospheric deposition program provides: 1) participation and leadership in the National Atmospheric Deposition Program (NADP) and 2) scientific research and assessment to evaluate trends and the effects of atmospheric deposition on aquatic and terrestrial ecosystems.

      image of fact sheet Atmospheric Deposition Program, U.S. Geological Survey Fact Sheet, 2000, 112-00: 27:36

National Atmospheric Deposition Program (NADP)
The NADP monitors wet atmospheric deposition at approximately 300 locations  throughout the United States. The USGS supports 76 of the roughly 250 NADP National Trends Network sites which measure acidity, nutrients and other major ions in precipitation. The USGS also supports 1 of the approximately 100 sites in the NADP Mercury Deposition Network which measure total and methyl mercury in precipitation. A fundamental NADP program objective is to provide scientists, resource managers and policy-makers world-wide with a long-term, high-quality database of atmospheric deposition to support research and decision-making in the areas of air quality, water quality, agricultural effects, forest productivity, materials effects, ecosystem studies, watershed studies, and human health.

NTN map
NADP - National Trends Network and 2021 Inorganic Nitrogen Deposition (November, 2021)


NADP - Mercury Deposition Network and 2021 Precipitation-weighted Mean Hg Concentration (November, 2021)

red dots = USGS supported sites
black dots = Other sites

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Page Last Modified: 11/30/2021