STATE AND NATIONAL AMBIENT AIR QUALITY STANDARDS
The state ambient air quality standards and the corresponding NAAQS are listed in the .pdf file at the bottom of this page. The Nevada standards shall be used in considering whether to issue a permit for a stationary source and shall ensure that the stationary source will not cause the Nevada standards to be exceeded in areas where the general public has access.
Although the national one-hour standard for O3 was supplemented with an eight-hour standard effective September 16, 1997, and new national standards for PM2.5 were added, the state standards will not reflect these changes until the federal implementation guidance has been issued and regulation changes can be adopted. The state has conducted ambient monitoring for PM2.5 since 1999. In February 2004 the State recommended all of Nevada be designated unclassifiable/attainment for PM2.5 and in June 2004 the EPA responded in agreement. The EPA Region 9 final designations of attainment status for the PM2.5 standards are expected to be made the end of 2004.
Excluding the 1997 national standards, which were challenged in the courts, the state standards and national primary standards for criteria pollutants are the same or approximately the same with the exceptions of O3 in the Lake Tahoe basin and eight-hour CO above 5,000 feet elevation. For these exceptions, the state standards are more stringent than the national standards. Furthermore, a violation of a short term standard for CO or SO2 is generally not incurred under national standards until the second annual exceedance, while a violation is incurred under the state standards for all pollutants at the first exceedance.
Determinations of violations of the national primary standards for PM10 and O3 are complicated by the need to round 24-hour PM10 concentrations to the nearest 10 µg/m3 and to determine "expected" values based on calculations involving the most recent three or more years' data, in accordance with 40 CFR 50, Appendix K. Appendix N to 40 CFR 50 is not used for comparisons to the PM10 standards because the 1997 PM10 standards were vacated by the courts (D.C. Circuit, May 14, 1999). The PM10 data presented in this report have not been manipulated according to the national method for determining attainment of the national ambient air quality standards. Instead, they are raw data suitable for comparison with the state standards.
Comparisons to the national PM2.5 standards are complicated by the need to compare to the 24-hour standard the 98th percentile of the distribution of the 24-hour concentrations for a period of one year, averaged over three years.
Finally, the national one-hour O3 standard is attained when, based on a three-year average, the expected number of days per year with a maximum hourly average above the standard is not more than one. The one-hour O3 standard was supplemented on September 16, 1997 with a national eight-hour standard, which is based on a three-year average of the annual fourth-highest daily maximum eight-hour average O3 concentrations.