Cal. Code Regs. Tit. 17, div. 3, ch. 1, subch. 1.5, art. 3, app 1
This Appendix describes the criteria to be used in determining the representativeness of individual air quality measurements and statistics for the purpose of designating areas as described in this article. Data representativeness, as that term is used herein, relates to the determination of whether the amount of data reflected in an individual air quality measurement or statistic is sufficient to characterize reliably air quality during the respective averaging time of a state standard. The criteria for determining data representativeness are summarized in the accompanying table and discussed further, below.
Air quality measurements and statistics are usually computed from short term observed values. If all the short term values for the statistical time period are available, the calculated statistic is representative. However, because all the short term values for a given period often are not available, a minimum number of observations are needed to provide reasonable assurance that the calculated measurement or statistic is a reliable estimate for the averaging time specified in the state standard.
In general, air quality measurements and statistics are considered representative if a minimum of 75 percent of all the potential short term values are included and are distributed throughout the entire statistical time period. This 75 percent criteria must be met from the averaging time of the initial measurement, up to and including, the final averaging time reflected by the air quality measurement or statistic. For example, a maximum daily statistic must meet the representativeness criteria specified for a "Day." Because a daily statistic reflects a single day, it does not need to meet the representativeness criteria for any other level (Month, Quarter, or Year). In evaluating data representativeness, all measurements are considered, including those identified as affected by a highly irregular or infrequent event under the "Air Resources Board Procedure for Reviewing Air Quality Data Possibly Affected by a Highly Irregular or Infrequent Event," set forth in Appendix 2 to this article.
Individual air quality measurements and statistics used for designating an area as attainment, nonattainment-transitional, or nonattainment must be representative. Furthermore, to ensure that the group of air quality measurements or statistics used for designating an area as attainment or nonattainment-transitional reflect the time of day and the season of expected high concentrations, these data must also be complete under the "Criteria for Determining Data Completeness" set forth in Appendix 3 to this article. In contrast, the air quality measurements or statistics used for designating an area as nonattainment are not required to be complete.Criteria for Representativeness of Air Quality Measurements and Statistics
Cal. Code Regs. Tit. 17, div. 3, ch. 1, subch. 1.5, art. 3, app 1
2. Amendment of first and third paragraphs filed 8-26-99; operative 9-25-99 (Register 99, No. 35).
3. Amendment filed 6-7-2004; operative 7-7-2004 (Register 2004, No. 24).