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No Valid Measurement(s)

  • There is not a valid hourly average available for one or more hours.
  • There are a number of reasons these averages may not be available.
  • TCEQ uses an automated collection system which analyzes all of the data as it is collected. Based on conditions at the site and the state of the instruments, the system may decide to automatically reject data. TCEQ personnel also continuously review the data and may decide to manually reject data.
    • Rejected data is flagged in various ways depending upon why it was rejected.
    • The flags show up in the hourly average report as characters instead of a data value.
    • The following are codes that may be applied to data:
      • NA - The average cannot be computed until all the measurements are received. This average will not be available until enough data has been received for the current or past hour.
      • 5PPB - Unblended standard check conducted at 5 ppb-V.
      • AQI - Data rejected by TCEQ validators. The TCEQ validators have reviewed the data and determined that it is not valid.
      • ARC - Acetylene response check.
      • AUDI - Audit sample.
      • BLAN - Blank sample.
      • CACS - Compressed air comparison sample.
      • CAL - Automatic calibration in progress. Calibrations are performed when instruments are changed or fail a span check and last from 3 to 6 hours. Non-scheduled calibrations may be initiated at any time by TCEQ field operators - usually during the course of instrument repair/replacement or troubleshooting.
      • DCSD - Daily Cal check standard duplicate.
      • DLA - Detection limit analysis.
      • EXP_ - Experimental or bad sample.
      • FEW - Not enough five-minute measurements available to create an hourly average. There must be 45 minutes of data available each hour in order for a valid hourly average to be created.
      • LIM - Data exceeds automatic criteria for rejection.
        • For meteorological parameters, this indicates that the measurements fall outside the EPA guidelines for meteorological collection of data. This is usually due to a short-term meteorological condition, such as rapid heating during the day or extended periods of calm winds.
        • For pollution parameters, this indicates that the instrument failed a scheduled automatic calibration or span check. Calibrations are performed periodically to insure that the instrument is functioning properly and the data collected is valid. If a calibration is failed, TCEQ field operators will go to the monitoring station to determine why the automatic calibration failed. Once the problem has been identified and corrected, a fresh calibration will be done on the instrument and valid data will start being collected.
      • LST - Lost data. Usually indicates that data was never collected. This may also be triggered by delays or breakdowns in data communications. Try retrieving the data later.
      • MAL - A malfunction that voids the data has occurred. The operator has determined that the data is not valid and should be ignored.
      • MUL - This is only seen on NOx monitors. This indicates that the sum of NO and NO2 measured at a site does not balance with the amount of NOx measured at a site. This usually indicates a problem in the instrument adjustment.
      • NEG - The measurement exceeds a lower limit and has too negative a value. It is possible to get small negative values under routine conditions, but large negative numbers indicate a problem in the data collection system.
      • NOD - Not Detected. The compound was not detected at a concentration that could be reliably quantitated. This may mean the compound is present but had interferences present, was below the detection capability of the instrument, or not present at all.
      • NOL - Instrument is not on line. The instrument is collecting data, but it has not been calibrated and the data it collects is ignored.
      • PMA - Preventive maintenance. Indicates the instument or monitoring site is undergoing maintenance and data collected is not valid data.
      • QAS - Quality Control audit in progress. TCEQ conducts periodic Quality Control audits on each monitoring site.
      • QRE - Data rejected because of failed or poor quality assurance results.
      • RAS - Radian audit sample.
      • RT_S - 55-component standard sample.
      • SPN - Automatic span check in progress. This is to check that the instrument calibration is holding. Span checks are generally performed once a week on each instrument and last from 2 to 4 hours. Non-scheduled span checks may be initiated at any time by TCEQ field operators - usually during the course of troubleshooting.
      • SPZ - Automatic span check in progress. This is a short instrument challenge to check that the instrument calibration is holding. These span checks are generally performed once a day on instruments and last 30 minutes. These are normally only seen if the system detects an instrument problem during the span check.
      • UNK - Unknown flag found in data.
  • Each time data is automatically rejected, TCEQ personnel review the data to determine if the automatic rejection is warranted or if there are circumstances which warrant recovery of the measurements.
  • Recovered and rejected data will be reflected in the hourly average report after it has been reviewed by TCEQ personnel.