Data validation is necessary because serious errors in data analysis and modeling results can be caused by erroneous individual data values. With the support of EPRI and the U.S. Environmental Protection Agency (EPA), STI developed volatile organic compound (VOC) data validation and analysis software named VOCDat. STI has provided this software at no cost to local, state, and regional agencies throughout the United States for use in preparing their VOC data for submittal to the EPA's data repository (AQS, formerly AIRS). VOCDat enables an analyst to screen VOC data for outliers and display data using scatter, fingerprint, and time series plots. VOCDat handles 1-hr, 3-hr, 8-hr, and 24-hr data and imports and displays other air quality parameters such as toxic compounds, speciated PM2.5, ozone, NOx, and meteorological data.
VOCDat software and its user guide can be downloaded free from http://vocdat.sonomatech.com/.
Scatter plots are useful for assessing the relationships between different species.
Fingerprint plots show the concentrations of each species in a sample (for VOCs, it is best to place them in chromatographic order) and help to identify unique characteristics of the samples.
Time series plots are useful for investigating the diurnal behavior of pollutants (and for data validation).
VOCDat includes three screening tests to aid analysts in determining which data should be flagged. These tests are checks of abundant species concentrations (checks for typically abundant species below detection when several others are present well above detection), comparison of concentrations (checks for violations of typical chemical relationships), and variability in concentrations (lists statistical outliers for selected species).
