Ca 2+ Cl - HNO3 HNO3- K + Mg 2+ Na + NH3 NH4+ NO3- NOx NOy O3 PM2.5 SO2 SO42-
Western Reference SitesDownload Image
Eastern Reference SitesDownload Image
1 The NAAQS was revised from 0.075 ppm to 0.070 ppm on October 15, 2015.
2 To attain this standard, the 3-year average of the fourth highest DM8A O3 concentrations measured at each monitor within a specified area must not exceed 0.070 ppm or 70 parts per billion (ppb) in practice (effective December 28, 2015). Ozone concentrations are commonly presented in units of ppb.