NADP/NTN

National Atmospheric Deposition Program (NRSP-3)/National Trends Network, NADP/NTN Coordination Office, Colorado State University Fort Collins, CO, 1992. 

Precipitation sampling networks in the United States generally collect either daily (UAPSP, MAP3S) or weekly (NADP, NTN) samples. 

The maps in Fig. 8.6(a) and Fig. 8.6(b) show average concentrations of Na and Cl in rain over the contiguous United States for 1994 (NADP/NTN, 1996). The high concentrations along coastlines reflect the contribution of wind-blown salt spray, particularly within 100 to 300 km of the ocean. 

Since 1986, the National Atmospheric Deposition Program (NADP/NTN) has collected weekly precipitation samples from alx>ut 200 monitoring sites nationwide in the United States. Sites are away from major point sources and large urban centers to provide a more regional/national perspective on precipitation chemistry. 

National Atmospheric Deposii ion Proouam (NRSP-3)/ Nationai Trends Nhtw ork. 1996. NADP/NTN Coordi-... 

The most widely used sampler in the United States networks today is comprised of two buckets, and a rain-activated switch to operate a movable cover. During non-precipitating periods, the cover remains tightly sealed on one bucket. Precipitation falling on the sensitive switch completes an electrical circuit activating a motor which lifts the cover from one side and places it on the opposite bucket. The sampler thus provides a dry sample as well as a wet sample. This is the standard instrument used throughout the NADP/NTN network. 

For example, the NADP/NTN allows extraction of a few milliliters for the field determination of pH and conductivity. Immediately after the aliquot has been withdrawn, the sample is sealed and then shipped to a central laboratory for further chemical analysis. Shipment of the sample is an important consideration for any type of sampling program since one must be sure that the collecting vessel does not leak in transit. 

It was stated at the outset that no dry deposition monitoring method has been decided and approved, but the dry bucket data from the precipitation network are available and, perhaps, are a source of some information. The total deposition was calculated at five sites in the NADP/NTN network and the percentage that was observed wet and dry was determined. The sites are located in east-central Illinois, northeast Ohio, southeast New York, central North Carolina, and extreme southwest North Carolina. All sites are rural in character with the southwest North Carolina site standing in a forest clearcut area. The data are shown in Figure 8. Recall the point made earlier that the first three ions shown in the figure are related to crustal dust. At all but one of the sites, these ions are... 

Figure 7. The pH (top), sulfate deposition (first down from the top), precipitation (first up from the bottom), and the sulfate concentration (bottom) from the Bondville, Illinois NADP/NTN network site.

Figure 8. The total and percent wet and dry deposition at selected NADP/NTN network sites.

National Atmospheric Deposition Program (1988). NADP/ NTN Annual Data Summary. Precipitation Chemistry in the United States, 1987. National Resources Ecology Laboratory, Colorado State University, Fort Collins, Colorado, 353 pp. 

National Atmospheric Deposition Program/National Trends Network (NADP/NTN) Site Visitation Program for the Period October 1987 through September 1988 Summary Report... 

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