The Environmental Protection Agency (EPA) will soon announce the results of its review of the existing regulations and possibly announce tightening of ozone limits.

The current limit—75 parts per billion (ppb) averaged over 8 hours—was set in March 2008. The Clean Air Act requires EPA to review, and, if necessary, revise the rule every five years.

Ozone (O₃) is a colorless, unstable toxic gas with a pungent odor and powerful oxidizing properties. It is harmful to breathe and damages crops, trees and other vegetation. It forms when sunlight acts on oxides of nitrogen or volatile organic compounds (VOC), so it is common in the summer in industrial and vehicle-heavy urban areas.

As shown on the map, many parts of the United States are periodically out of compliance with the current standards. Lower limits will certainly force many state and local governments to impose additional requirements to reduce emissions of the compounds that form ozone.

The arguments for and against lower ozone limits:

• The EPA science advisory committee said "ample scientific evidence" exists that ozone is harmful at lower levels than previously thought, citing studies showing it decreased lung function and increased respiratory symptoms and airway inflammation even at concentrations of 70 parts per billion.
• On the other hand, the National Association of Manufactures reports that tighter ozone standards could cost industry $270 billion per year. In addition, a lower limit—60 to 70 ppb levels are expected--could restrict oil and natural gas exploration production operations.

EPA reports that air quality has improved for many common pollutants. Among these, ozone concentrations have improved 33 percent from 1980 to 2013 and 18 percent from 2000 to 2013.

Looking at the precursors of ozone, EPA reports that VOC emissions have declined from 17 million tons per year in 2000 to 14 million tons in 2013. Over the same period oxides of nitrogen declined from 22 to 13 million tons per year.

Industry supporters have recommended that EPA delay changes in the ozone standards until it sees the full impact of its 2015 deadline for “green” or low emission completions for new natural gas wells. The early adoption by many operators of the low-emission requirements may be contributing to improved air quality.

For updates on the status of ozone regulations, follow AAPG’s policy tweets @GeoEnergyPolicy.