USGS External Quality Assurance Project Studies - Improving National Atmospheric Deposition Program Data Acquisition and Interpretation

Gregory A. Wetherbee and Natalie E. Latysh
U. S. Geological Survey, Branch of Quality Systems

The U.S. Geological Survey (USGS) implements external quality assurance programs to measure and improve the integrity of National Atmospheric Deposition Program (NADP) data and datacollection systems. In addition to several long-term quality assurance studies, the USGS is evaluating four data-collection systems and their interpretation: 1) data telemetry systems for network monitoring and management; 2) altitude-dependent isopleth maps for spatial representation of atmospheric deposition; 3) wind shielding precipitation collectors to improve snow catch; and 4) urbanization of NADP sites.

Replacement of Belfort recording rain gages with more sophisticated electronic gages (ETI Noah-IV and OTT Pluvio-N) enables sites to be monitored remotely using telemetry systems. The USGS is evaluating two different satellite telemetry platforms and a cellular phone-based system to transmit data in near-real time. The near-real time data can inform site operators and network coordinators of instrument malfunction to limit lost data, improve representativeness of the NADP data, and assist in qualification of data.

Research of high altitude ecosystems would benefit from more accurate interpolated estimates of precipitation used in preparing NADP maps of annual wet deposition and annual precipitationweighted mean concentration. The Parameter-elevation Regressions on Independent Slopes Model (PRISM) uses point measurements of precipitation and a digital elevation model (land surface altitude) to produce digital grid estimates of precipitation depth. The resulting maps using PRISM and NADP precipitation chemistry provide more realistic illustrations of total annual wet deposition in high altitude areas with complex terrain such as the Rocky Mountains. Estimation of the error inherent in the maps is needed before further consideration of using PRISM to create the maps.

USGS is preparing to operate two co-located AeroChem Metrics precipitation collectors at the National Center for Atmospheric Research Marshall Field Site, located between Golden and Boulder, Colorado. One collector will be operated using standard NADP methods and the other using a fabric wind shield attached to the collector. Weekly catch efficiency differences will be monitored and, if warranted, chemical measurements will be made.

Finally, the project is preparing to study trends indicative of urbanization near selected NADP sites. Most NADP sites were located to measure regionally representative precipitation chemistry. Population growth and expansion of industry is occurring near sites originally selected to be unimpacted by local emission sources. The USGS study will attempt to identify which, if any, NADP sites are collecting data indicative of urban encroachment.