Field Methods:
Every Tuesday morning at 9:00 a.m., NTN site operators across the country head to their monitoring stations to retrieve their samples of the previous week’s precipitation, whether rain, snow, or sleet.

Samples are collected continuously in a wet deposition collector. The collector opens automatically during wet weather, allowing the precipitation to fall into a collection bucket lined with a sample bag, and then closes as soon as the precipitation stops.

At the site, the operator replaces the collection bucket and bag with one a new each week. The operator then takes the sample to a field laboratory, where it is weighed. Next, the sample is transferred to a shipping bottle and sent to the NAL in Madison, Wisconsin.

Each site is also equipped with a weighing-bucket rain gauge that provides a continuous record of rainfall amounts. Rainfall is recorded to the nearest 0.01 in. The rain gauge also monitors the wet deposition collector, recording whether the collector was properly open during wet periods and closed during dry periods.

Lab Methods:
At the NADP Analytical Laboratory (NAL), the concentrations of the important inorganic chemicals in precipitation are analyzed. These chemicals or analytes include acidity (measured as pH), sulfate, nitrate, ammonium, chloride, and base cations.

The data are checked to ensure their quality, and special codes are applied to help in interpreting the data. These sample validity codes indicate the quality of the sample, for instance, whether it was collected according to standard protocols and whether there is any sign of contamination.

After this initial data processing, the data are sent electronically to the NADP Program Office, which performs further checks of accuracy and completeness. The entire data record is confirmed as being consistent with standard NTN procedures and documentation. Sophisticated data processing programs are run to detect discrepancies in the coding of the sample validity and completeness of each sites data records. Any such discrepancies are carefully screened and resolved.

Only after data verification is complete is the sample record entered into the NADP database, ready for distribution to the public and inclusion in NADP publications.

The current listing of laboratory SOPs are available. Copies are available upon request.