Quality Assurance in the National Atmospheric Deposition Program for Support of Atmospheric Trends Research

摘要

The National Atmospheric Deposition Program(NADP)has established Quality Assurance(QA)and Quality Control(QC)procedures to assure that data of defined quality are provided to support atmospheric deposition research.The NADP measures chemical concentrations and precipitation amounts at over 300 sites in North America to determine wet deposition from precipitation.NADP sites are required to meet minimum siting standards,use approved equipment,and follow standard operating procedures.Additionally,the NADP analytical laboratories operate under well-defined QA programs with well-defined QC criteria.Established evaluations provide information to quantify the primary data quality indicators of precision,bias,completeness,representativeness,comparability,and sensitivity.To evaluate the performance of NADP QA/QC programs,a trend analysis was performed at twenty National Trends Network(NTN)sites using the nonparametric Kendall trend test.Precipitation amounts,and chemical concentrations of calcium,magnesium,potassium,sodium,sulfate,nitrate,chloride,ammonium,and hydrogen ion were evaluated.The variability in the trend estimate was compared with the total measurement variability,as assessed by measurements at collocated sites.Overall,the variability of collocated site data was lower than the variability of the trend estimates.This indicates that the variability observed in NTN data primarily reflects real changes in precipitation composition,and not the variability of the measurement system.Therefore,data quality goals can be set for the primary data quality indicators to ensure that trends can be quantified with known certainty using NADP data.