A quality control (QC) procedure for eliminating spurious measurements of PM2.5 from a network of ground observations has been developed by the team from NASA/MSFC participating in the HELIX-Atlanta Respiratory Health Team led by the CDC. The procedure utilizes observations from surrounding sites to determine whether a given measurement is acceptable or is considered erroneous and thus eliminated from further analysis. The QC procedure is based on a non-parametric (rank-order) spatial analysis. This method does not make the assumptions often present when using parametric statistics.
Purpose
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Methodology
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Figure 1: Defining Neighbors |
Figure 2. Test Statistic Distribution
Surface EnhancementThe filtered EPA AQS observations have then been used to generate spatially continuous ground-level PM2.5 surfaces in order to estimate exposure to the local population using the B-Spline surfacing technique. Figure 3 shows an example how using the quality control procedure enhanced the output PM2.5 surfaces by preventing any unrealistic ripples to be formed within the surface. The location of the wild value is indicated by the green arrow. Data are from the EPA AQ network for October 9, 2003. |
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Figure 3. PM2.5 B-Spline surface for October 9 2003 (a) without and (b) with QC procedures
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Additional InformationCDC:National EPHT Program (epht@cdc.gov) NASA: Dale Quattrochi (Dale.Quattrochi@nasa.gov) Doug Rickman (Douglas.L.Rickman@nasa.gov) EPA: Solomon Pollard(Solomon@epamail.epa.gov) Web: http://www.cdc.gov/nceh/tracking/helix.htm |
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