The Environmental Protection Agency (EPA) is taking final action to make a technical correction to equation 2 in appendix N to part 50, section 4.4(b) of the National Ambient Air Quality Standards (NAAQS) for Particulate Matter. Equation 2 in appendix N describes an intermediate step in the calculation of the design value for the annual PM<INF>2.5</INF> (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) NAAQS. This action corrects Equation 2 to properly account for cases where a site has quarters without daily values and passes the minimum quarterly value data substitution test. This change accurately reflects the intended calculation of the annual PM<INF>2.5</INF> design value and is consistent with the text of section 4.1 in appendix N to part 50.