Impact of percentile computation method on PM 24-h air quality standard

► US EPA uses the average of the percentile values for 3 years to determine attainment. ► US EPA NAAQS percentile values were compared with the actual 98th percentile values. ► Regression analysis found high correlation coefficients. ► The two methods showed substantial agreement. ► Either approach could serve as the statistical form of the 24-h PM standard.