Dry Deposition Monitoring

Overview

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.

CASTNet site at Glacier National Park, Montana

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).

Dry deposition of particles and gases occurs by complex processes such as settling, impaction, and adsorption. Dry deposition is monitored through the Clean Air Status and Trends Network (CASTNet).

Locations

The National Park Service maintains many deposition monitoring sites across the country. For a larger map and table of sites, please visit our Deposition Monitoring Locations web page.

Procedures

Inside CASTNet shelter at Yellowstone
National Park, Wyoming

CASTNet measures weekly average atmospheric concentrations of sulfate, nitrate, ammonium, sulfur dioxide, and nitric acid; and meteorological conditions. Filter packs are exposed for 1-week intervals at a flow rate of 1.5 liters per minute (3.0 liters per minute for western sites), and sent to the contracted laboratory in Gainesville, Florida, for chemical analysis. Dry deposition rates are calculated using atmospheric concentrations, meteorological data, and information on land use, vegetation, and surface conditions.

Data

Results

The following maps show total deposition, including both wet and dry components for 2002. Dry deposition rates are calculated using the Multi-layer Leaf Model (MLM). Total deposition is reported below in terms of kilograms per hectare per year for sulfur and nitrogen.

Total sulfur deposition is much higher in the Eastern U.S. than in the Western states. With few exceptions, wet deposition is the major contributor to total deposition of sulfur.

Total deposition of nitrogen is also higher in the Eastern U.S., however higher rates are also estimated for the Rocky Mountains. Again, most sites are dominated by wet deposition, however the majority of nitrogen deposition to Joshua Tree NP and Death Valley NP in southern California occurs as dry deposition. Annual reports for individual park service stations are available from the NPS, and annual network reports are available from the CASTNet web site.

Contacts