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Title 40

Displaying title 40, up to date as of 6/16/2026. Title 40 was last amended 6/15/2026.
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  1. Title 40 —Protection of Environment
  2. Chapter I —Environmental Protection Agency
  3. Subchapter C —Air Programs
  4. Part 50   View Full Text
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Title 40Protection of EnvironmentPart / Section
Chapter IEnvironmental Protection Agency1 – 1099
Subchapter CAir Programs50 – 99
Part 50National Primary and Secondary Ambient Air Quality Standards50.1 – 50.21
§ 50.1Definitions.
§ 50.2Scope.
§ 50.3Reference conditions.
§ 50.4National primary ambient air quality standards for sulfur oxides (sulfur dioxide).
§ 50.5National secondary ambient air quality standard for sulfur oxides (sulfur dioxide).
§ 50.6National primary and secondary ambient air quality standards for PM10.
§ 50.7National primary and secondary ambient air quality standards for PM2.5.
§ 50.8National primary ambient air quality standards for carbon monoxide.
§ 50.9National 1-hour primary and secondary ambient air quality standards for ozone.
§ 50.10National 8-hour primary and secondary ambient air quality standards for ozone.
§ 50.11National primary and secondary ambient air quality standards for oxides of nitrogen (with nitrogen dioxide as the indicator).
§ 50.12National primary and secondary ambient air quality standards for lead.
§ 50.13National primary and secondary ambient air quality standards for PM2.5.
§ 50.14Treatment of air quality monitoring data influenced by exceptional events.
§ 50.15National primary and secondary ambient air quality standards for ozone.
§ 50.16National primary and secondary ambient air quality standards for lead.
§ 50.17National primary ambient air quality standards for sulfur oxides (sulfur dioxide).
§ 50.18National primary ambient air quality standards for PM2.5.
§ 50.19National primary and secondary ambient air quality standards for ozone.
§ 50.20National primary ambient air quality standards for PM2.5.
§ 50.21National secondary ambient air quality standards for sulfur oxides (sulfur dioxide).
Appendix A-1 to Part 50
Reference Measurement Principle and Calibration Procedure for the Measurement of Sulfur Dioxide in the Atmosphere (Ultraviolet Fluorescence Method)
Appendix A-2 to Part 50
Reference Method for the Determination of Sulfur Dioxide in the Atmosphere (Pararosaniline Method)
Appendix B to Part 50
Reference Method for the Determination of Suspended Particulate Matter in the Atmosphere (High-Volume Method)
Appendix C to Part 50
Measurement Principle and Calibration Procedure for the Measurement of Carbon Monoxide in the Atmosphere (Non-Dispersive Infrared Photometry)
Appendix D to Part 50
Reference Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere (Chemiluminescence Method)
Appendix E to Part 50 [Reserved]
Appendix F to Part 50
Measurement Principle and Calibration Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase Chemiluminescence)
Appendix G to Part 50
Reference Method for the Determination of Lead in Total Suspended Particulate Matter
Appendix H to Part 50
Interpretation of the 1-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone
Appendix I to Part 50
Interpretation of the 8-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone
Appendix J to Part 50
Reference Method for the Determination of Particulate Matter as PM10 in the Atmosphere
Appendix K to Part 50
Interpretation of the National Ambient Air Quality Standards for Particulate Matter
Appendix L to Part 50
Reference Method for the Determination of Fine Particulate Matter as PM2.5 in the Atmosphere
Appendix M to Part 50 [Reserved]
Appendix N to Part 50
Interpretation of the National Ambient Air Quality Standards for PM2.5
Appendix O to Part 50
Reference Method for the Determination of Coarse Particulate Matter as PM10-2.5 in the Atmosphere
Appendix P to Part 50
Interpretation of the Primary and Secondary National Ambient Air Quality Standards for Ozone
Appendix Q to Part 50
Reference Method for the Determination of Lead in Particulate Matter as PM10 Collected From Ambient Air
Appendix R to Part 50
Interpretation of the National Ambient Air Quality Standards for Lead
Appendix S to Part 50
Interpretation of the Primary National Ambient Air Quality Standards for Oxides of Nitrogen (Nitrogen Dioxide)
Appendix T to Part 50
Interpretation of the Primary and Secondary National Ambient Air Quality Standards for Oxides of Sulfur (Sulfur Dioxide)
Appendix U to Part 50
Interpretation of the Primary and Secondary National Ambient Air Quality Standards for Ozone
eCFR Content