EPA is required to update its standard for each of the six main "criteria" air pollutants every five years. Each pollutant has been widely recognized as an important component or indicator of potential health and environmental degradation.
The update of the standard for nitrogen oxides (NOx) is far behind schedule - a situation typical with other criteria pollutants.
However, spurred in part by a pending court order, the agency has moved the process along - last completed in 1996 - by releasing on Aug. 31, 2007, its draft findings of the current science for NOx and its health effects. A 60-day public comment period ends Oct. 31, 2007, and a public meeting with the agency's Clean Air Scientific Advisory Committee (CASAC) is in the works for some time later this year. EPA: Suzanne Ackerman,  202-564-7819; release. 
If the full process goes in accordance with the pending court order, which is expected to be finalized in the next few months, other key dates - resulting in a new standard 14 years after the last one was approved, and 9 years later than required - will be:
- July 2008: Final science assessment
- January 2009: Final risk exposure assessment
- August 2009: Proposed rule
- May 2010: Final rule
To check on the final timing later this year, contact Robert Ukeiley, 859-986-5402, the attorney for the groups and individuals suing EPA to move ahead.
NOx emissions are generated primarily by combustion processes, from sources such as vehicles, electric utilities, and other fuel-burning industrial, commercial, residential, and natural generators.
The average concentration nationwide for nitrogen dioxide (NO2) - a commonly-occurring nitrogen oxide that is used for standard setting - has dropped sharply from 1980 to 2006, but has been flat the past three years: NO2 levels  (includes links to local sites, which vary significantly in their trend).
Various interest groups have just begun to focus on the NO2 standard, for which EPA acknowledges there has been significant new science developed in the past 11 years, after the current standard of 0.053 parts per million (or 100 micrograms per cubic meter) for an annual arithmetic mean was set: National Ambient Air Quality Standards. 
Along with the actual standard, the process by which it is being set is new, after EPA revised its procedures in December 2006. Background information.  This is the first criteria pollutant to be reviewed via the new process, which EPA says will expedite the approval of updated standards. Critics charge that it will increase emphasis on politics, decrease the weight given to science, and be less transparent to the public.
Some of the groups and people that likely will soon be good sources for comment include:
- Alliance of Automobile Manufacturers, Wade Newton,  202-326-5571.
- American Petroleum Institute, Howard Feldman,  202-682-8340.
- Electric Power Research Institute, Heather Lynch Hansen,  650-855-2017.
- National Association of Manufacturers: media,  202-637-3094.
- Clean Air Watch, Frank O'Donnell,  202-302-2065.
- Natural Resources Defense Council, John Walke,  202-289-2406.
- Deborah Shprentz  (often hired by the American Lung Association to review air pollution issues), 703-437-0959.
- George Thurston, New York University School of Medicine, and CASAC member, 845-731-3564.
- Praveen Amar,  Northeast States for Coordinated Air Use Management (NESCAUM), and CASAC member, 617-259-2026.
For more information on NOx:
- Health and environmental basics. 
- Draft science assessment  (includes link to Aug. 30, 2007, Federal Register notice, which is here ).
- Additional information. 
In February 2007, the California Air Resources Board (CARB) approved new NO2 standards, setting the annual average at 0.03 ppm, far below EPA's current standard of 0.053 ppm. In addition to establishing an annual standard for the first time, the state lowered its 1-hour-average standard from 0.25 ppm to 0.18 ppm; EPA doesn't have an equivalent short-term standard. Almost every part of the state is expected to continue meeting the standards, which are expected to go into effect soon.
- CARB: Patricia Rey,  916-322-2990; Review of the Ambient Air Quality Standard for Nitrogen Dioxide.