Technical Correction to the National Ambient Air Quality Standards for Particulate Matter

The Environmental Protection Agency (EPA) is taking direct final action to make a technical correction to an equation in an appendix in the National Ambient Air Quality Standards (NAAQS) for Particle Pollution. Equation 2 describes an intermediate step in the calculation of the design value for the annual PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) NAAQS. This action corrects a scrivener's error in one of the equations used to calculate an annual mean PM2.5 concentration, to properly account for cases where a site does not have four complete quarters of data and passes one of two substitution tests. This change accurately reflects the intended calculation of the annual mean PM2.5 design value and is consistent with the text elsewhere in the appendix.