Quality Assurance Support for the NADP


The concentrations of dissolved substances in precipitation are generally quite low (less than 1% of NADP precipitation samples have total dissolved chemical concentrations > 20 mg/L). Chemical measurements of precipitation samples require thorough quality assurance (QA) and quality control (QC) procedures to assure that meaningful data are obtained. Biases can result from: sample handling contamination; losses to sample container walls; chemical, physical, and biological changes; and variations in collection and analytical procedures. Stringent QA and QC procedures are essential for obtaining unbiased, precise, and representative atmospheric deposition measurements and for maintaining the integrity of the sample during collection, handling, and analysis. Equally stringent procedures must be applied to data management to assure data accuracy is maintained.

QA is stressed in all aspects of NADP operations. Sites are required to meet minimum siting standards, use approved instruments, and follow standard procedures. The NADP Analytical Laboratory (NAL) operates under well-defined QA programs with well-defined QC criteria. QA continues for processing, coding, and reporting data to the Program Office. QA procedures, however, are not a static sets of rules. They are modified to accommodate program changes and in response to the experience accumulated from past practices. NADP QA programs are aimed toward providing representative data of documented bias, precision, and completeness to assist data users in evaluating the appropriateness of the data for a particular application. Specifically, it is the NADP quality management policy to accomplish the following:

  • Develop scientifically-based methodologies for data collection and assessment to provide continued quality improvement.

  • Provide quality assessments of network operations to assist network management and cooperating agencies in improving network monitoring strategies.

  • Provide estimates of completeness, precision, bias and representativeness for all spatial and temporal data values reported.

  • Provide complete and concise records of NADP policies, procedures and quality assessments.

  • Permanently associate network quality assurance documentation with reported data.

QA Plans
QA Reports

NADP Analytical Laboratory (NAL)



Atmospheric Mercury Network (AMNet)

External Site Survey Program

External Siting Criteria Evaluations

The NADP Site Selection and Installation Manual outlines 24 siting criteria rules for both NTN and MDN wet deposition collectors, along with 16 or 19 siting criteria guidance guidelines for NTN or MDN, respectively. External siting criteria evaluations performed by Environmental Engineering and Measurement Services (EEMS) and published within their NADP Site Survey Program Annual Report showed that about 80% of sites failed to meet all siting criteria. To address this, a NADP QAAG Siting Criteria Workgroup was formed in 2020. Despite widespread siting criteria violations, only a few had statistically significant negative impacts on data completeness. By downgrading certain criteria from rules to guidance and focusing solely on siting criteria rules, the percentage of collectors meeting all criteria assessments increased from 23% to 85% in 2022, indicating substantial improvement attributed to the hard work of the siting criteria workgroup.

External QA Program
  1. MDN Interlaboratory Comparison Program,
  2. MDN System Blank Program,
  3. NTN Interlaboratory Comparison Program,
  4. NTN Field Audit Program, and
  5. Collocated Sampler Program.
  6. U.S.EPA – Site Visitation Program
Laboratory SOPs

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

QA/QC Issues
  • Notice regarding pH data analyzed from June 1, 2018 through February 4, 2020

    This includes NTN sample IDs TT0001SW-TV1558SW and AIRMoN samples AE001L-AE0769L. This pH data set may have a slight bias due to the use of an incorrect pH meter calibration curve. All quality control samples associated with pH analysis during this timeframe met criteria (unless qualified otherwise) and thus the sample data are considered valid. However, a small pH bias of +/- 0.2 S.U. was detected when comparing samples analyzed with the corrected calibration to the original calibration. Low bias was observed for samples with pH < 5.6 and a high bias for samples with pH > 5.6. In no case was the measured difference greater than 0.2 pH units. Please contact the Laboratory QA Specialist Nichole Miller if you need additional information about this issue.

  • Br data was removed on October 15, 2019

    The NADP Analytical Laboratory (NAL) determined that web-published bromide data from January 2012 through June 2018 have a known or suspected bias caused by the presence of oxalate in the precipitation. Motions to remove these data from the NADP website and discontinue bromide as an official NADP analyte (due to >80% non-detects) were presented to the NADP Executive Committee on May 17, 2019 and were approved.

    This note serves as notification that these motions have been executed – all bromide data, including maps, was removed from the NADP website on October 15th, 2019; and as of June 1st, 2019 the NAL is no longer quantifying bromide. Preliminary, summary and individual sample reports will no longer include bromide results (though for a period of time the published data file format will continue to include the bromide column, but without analytical results).

    Bromide data from June 2018 through June 2019 (which is valid) and the larger bromide data set will be archived and made available upon request. A link to documents providing background on this bromide issue will be placed on the NADP website. Please contact David Gay with any questions and data requests.

  • CAL Readiness Verification Report

    This report presents the results of quality assurance (QA) studies conducted to verify the performance of the Wisconsin State Laboratory of Hygiene (WLSH) as the new NADP Analytical Laboratory (NAL) for the National Atmospheric Deposition Program (NADP). A Readiness Verification Plan (RVP; QAAG, March 16, 2018) was developed that details the objectives, study designs, and performance assessment metrics for the QA studies. The overarching goal of the RVP QA studies was to ensure that NADP data continue to be of sufficient quality to quantify trends in atmospheric chemistry, and importantly, that potential step-changes in data, which could be introduced as a result of analytical laboratory bias and variability, are identified, quantified, and minimized.

    Readiness Verification Plan

Past Issues

Other QA Information

Intercomparisons Between the NADP/NTN Monitoring Network and Other Networks

APIOS – Acid Precipitation In Ontario Study

  • Period of Intercomparison: October 1981 – September 1992
  • Locations Involved: (1 in the United States)
    • Fernberg, MN
  • Publications:

    Y. Zeng, P.K. Hopke, A study of the sources of acid precipitation in Ontario, Canada, Atmospheric Environment (1967), Volume 23, Issue 7, 1989, Pages 1499-1509, ISSN 0004-6981, https://doi.org/10.1016/0004-6981(89)90409-5.

CANSAP – Canadian Network for Sampling Acid Precipitation

CAPMoN – Canadian Air and Precipitation Monitoring Network

CARB – California Air Resources Board

  • Period of Intercomparison: April 1983 –
  • Number of Locations Involved: 4
    • Giant Forest (Sequoia National Park)
    • Montague
    • Tanbark Flat
    • Yosemite

EMEFS – Eulerian Model Evaluation Field Study

  • Period of Intercomparison: May 1988 – June 1990
  • Number of Locations Involved: 15 (not all networks operated in all locations)
    • Bondville, IL
    • Coweeta, NC
    • Fernberg, MN
    • Kane, PA
    • Land Between the Lakes, KY
    • Liley Cornet Woods, KY
    • Oxford, OH
    • Parson, WV
    • Pennsylvania State University, PA
    • Perryville, KY
    • Quabbin Reservoir, MA
    • Sutton, PQ
    • Underhill, VT
    • Washington Crossing, NJ
    • Whiteface Mtn, NY
  • Publications:
  • Daniel J. McNaughton, Robert J. Vet, Eulerian model evaluation field study (EMEFS): A summary of surface network measurements and data quality ,Atmospheric Environment, Volume 30, Issue 2, 1996, Pages 227-238, ISSN 1352-2310, https://doi.org/10.1016/1352-2310(95)00273-2.

MAP3S – Multi-state Atmospheric Power Production Pollution Study

  • Period of Intercomparison:
  • Number of Locations Involved:
    • Bondville, IL
    • Oxford, OH
    • Pennsylvania State University, PA
    • Whiteface Mtn, NY
QA Contacts

Systems QA Manager
Martin Shafer

Laboratory QA Specialist
Nichole Miller