5.3.2 Completeness Requirement

Regulatory analyses for the short-term ambient air quality standards (1 to 24-hour averaging) involve the sequential application of a dispersion model to every hour in the analysis period (one to five years); such analyses require a meteorological record for every hour in the analysis period. Substitution for missing or invalid data is used to meet this requirement. Applicants in regulatory modeling analyses are allowed to substitute for up to 10 percent of the data; conversely, the meteorological data base must be 90 percent complete (before substitution) in order to be acceptable for use in regulatory dispersion modeling. The following guidance should be followed for purposes of assessing compliance with the 90 percent completeness requirement:

• Lost data due to calibrations or other quality assurance procedures is considered missing data.



• A variable is not considered missing if data for a backup, collocated sensor is available.



• A variable is not considered missing if backup data from an analog system; which meets the applicable response, accuracy and resolution criteria; are available.



• Site specific measurements for use in stability classification are considered equivalent such that the 90 percent requirement applies to stability and not to the measurements (e.g., _E and _A ) used for estimating stability.



• The 90 percent requirement applies on a quarterly basis such that 4 consecutive quarters with 90 percent recovery are required for an acceptable one-year data base.



• The 90 percent requirement applies to each of the variables wind direction, wind speed, stability, and temperature and to the joint recovery of wind direction, wind speed, and stability.

Obtaining the 90 percent goal will necessarily require a commitment to routine preventive maintenance and strict adherence to approved quality assurance procedures (Sections 8.5 and 8.6). Some redundancy in sensors, recorders and data logging systems may also be necessary. With these prerequisites, the 90 percent requirement should be obtainable with available high quality instrumentation. Applicants failing to achieve such are required to continue monitoring until 4 consecutive quarters of acceptable data with 90 percent recovery have been obtained. Substitutions for missing data are allowed, but may not exceed 10 percent of the hours (876 hours per year) in the data base. Substitution procedures are discussed in Section 6.8

5. SYSTEM PERFORMANCE
 5.1 System Accuracies
 5.2 Response Characteristics of Meteorological Sensors
  5.3 Data Recovery
      5.3.1 Length of Record
      5.3.2 Completeness Requirement
  5.4 Recommendations