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        Ambient Air Quality Standards

        Monitoring Program - Pollutants of Concern

        The principal ambient air pollutants, based on public health concerns, have been identified by the U.S. Environmental Protection Agency (EPA) as "criteria" pollutants. The EPA established National Ambient Air Quality Standards (NAAQS) for these criteria pollutants. The standards of quality for ambient air in Nevada differ from EPA's and shall not be exceeded. Detailed information on each criteria pollutant may be found on EPA's criteria pollutant website.



        A: The Director shall use the Nevada standards 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.

        B: The National standards are used in determinations of attainment or nonattainment. The form of a National standard is the criteria which must be satisfied for each respective concentration level of a standard for the purposes of attainment. The form for each National standard is set forth in 40 C.F.R. Part 50 and may be viewed at http://www.epa.gov/air/criteria.html.

        C: Where applicable, concentration is expressed first in units in which it was adopted. All measurements of air quality that are expressed as mass per unit volume, such as micrograms per cubic meter, must be corrected to a reference temperature of 25 degrees Centigrade and a reference pressure of 760 mm of Hg (1,013.2 millibars); “ppm” in this table refers to parts per million by volume, or micromoles of regulated air pollutant per mole of gas; “µg/m3” refers to micrograms per cubic meter.

        D: Any reference method specified in accordance with 40 C.F.R. Part 50 or any reference method or equivalent method designated in accordance with 40 C.F.R. Part 53 may be substituted.

        E: National primary standards are the levels of air quality necessary, with an adequate margin of safety, to protect the public health.

        F: National secondary standards are the levels of air quality necessary to protect the public welfare from any known or anticipated adverse effects of a regulated air pollutant.

        G: The EPA revoked the National 1-hour ozone standard as it applies to all areas. However, anti-backsliding provisions in Federal law require certain areas to have continuing obligations under the National 1-hour ozone standard.

        H: The 1971 National sulfur dioxide standards remain in effect for an area until 1 year after the area is designated for the 2010 National sulfur dioxide standard, except that in an area designated nonattainment for the 1971 National sulfur dioxide standards, the 1971 standards remain in effect until an implementation plan to attain or maintain the 2010 National sulfur dioxide standards is approved.

        I: The ambient air quality standard for hydrogen sulfide does not include naturally occurring background concentrations.

        Exceptional Events

        An exceptional event is an unusual or naturally occurring event that can affect air quality but is not reasonably controllable. Occasionally, an exceptional event can cause an exceedance of the standards of air quality. The Environmental Protection Agency promulgated the Exceptional Events Rule on March 22, 2007 to treat data influenced by exceptional events that result in violations of the NAAQS. The Rule allows states to "flag" air quality monitoring data as an exceptional event and exclude that data from use in determining a violation of the NAAQS, if the U. S. EPA concurs with the demonstration submitted.

        State of Nevada Exceptional Event Demonstrations

        Table of the National Ambient Air Quality Standards
        PollutantPrimary/SecondaryAveraging TimeLevelForm
        Carbon Monoxide (CO)Primary8-hours9 ppmNot to be exceeded more than once per year
        1-hour35 ppm
        Lead (Pb)Primary and secondaryRolling 3-month average0.15 µg/m3Not to be exceeded
        Nitrogen Dioxide (NO2)Primary1-hour100 ppb98th percentile of 1-hour daily maximum concentrations, averaged over 3 years
        Primary and secondary1-year53 ppbAnnual mean
        Ozone (O3)Primary and secondary8-hours0.070 ppmAnnual fourth-highest daily maximum 8-hour concentration, averaged over 3 years
        Particle Pollution (PM)PM2.5Primary1-year12.0 µg/m3Annual mean, averaged over 3 years
        Secondary1-year15.0 µg/m3Annual mean, averaged over 3 years
        Primary and secondary24-hours35 µg/m398th percentile, averaged over 3 years
        PM10Primary and secondary24-hours150 µg/m3Not to be exceeded more than once per year on average over 3 years
        Sulfur Dioxide (SO2)Primary1-hour75 ppb99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
        Secondary3-hours0.5 ppmNot to be exceeded more than once per year

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