How is the air quality measure (number of days exceeding the NAAQS) calculated?
The air quality measure is the number of days that the maximum 8-hour ozone levels exceed the NAAQS. The maximum 8-hour daily concentration for ozone is determined by retaining data reported for each monitoring site that meet the minimum data completeness criteria set forth in the NAAQS (i.e. if valid 8-hour averages are available for at least 75% of possible hours in a day or the maximum 8-hour average is above the level of the standard). The values that exceed the NAAQS of 0.075 ppm (i.e., 0.076 and higher) are considered above the NAAQS.
