annual PM
(1) The 3-year average of PM2.5 annual mean mass concentrations for each eligible monitoring site is referred to as the annual PM2.5NAAQS DV. (2) The 3-year average of annual 98th percentile 24-hour average PM2.5 mass concentration values recorded at each eligible monitoring site is referred to as the 24-hour (or daily) PM2.5NAAQS DV.