The U.S. Environmental Protection Agency (EPA) proposed rules on November 26 to strengthen air quality standards to within a range of 65 to 70 parts per billion (ppb). The agency says it will take comments on a level as low as 60 ppb.

The Clean Air Act requires EPA to review the standards every five years. EPA last updated these standards in 2008, setting them at 75 ppb.

EPA says its scientists examined numerous scientific studies in its most recent review of the ozone standards, including more than 1,000 new studies published since the last update. Studies indicate that exposure to ozone at levels below 75 ppb -- the level of the current standard -- can pose serious threats to public health. Ground-level ozone forms in the atmosphere when emissions of nitrogen oxides and volatile organic compounds “cook” in the sun from sources like cars, trucks, buses, industries, power plants and certain fumes from fuels, solvents and paints.

EPA says health benefits will be gained from tighter standards. It valued the benefits at $6.4 to $13 billion annually in 2025 for a standard of 70 ppb, and $19 to $38 billion annually in 2025 for a standard of 65 ppb. Annual costs are estimated at $3.9 billion in 2025 for a standard of 70 ppb, and $15 billion for a standard at 65 ppb.

EPA says a combination of recently finalized or proposed air pollution rules – including “Tier 3” clean vehicle and fuels standards – will cut smog-forming emissions from industry and transportation, helping states meet the proposed standards. EPA’s analysis of federal programs that reduce air pollution from fuels, vehicles and engines of all sizes, power plants and other industries shows that the majority of U.S. counties with monitors would meet the tighter standards by 2025 with the rules and programs now in place or underway. Nationally, from 1980 to 2013, average ozone levels have fallen 33 percent. EPA projects that this progress will continue.

The Clean Air Act provides states with time to meet the standards. Depending on the severity of their ozone problem, areas would have between 2020 and 2037 to meet the standards. To ensure that people are alerted when ozone reaches unhealthy levels, EPA is proposing to extend the ozone monitoring season for 33 states.

The agency is also proposing to strengthen the “secondary” ozone standard to a level within 65 to 70 ppb to protect plants, trees and ecosystems from damaging levels of ground-level ozone. EPA says that new studies show that repeated exposure to ozone stunts the growth of trees, damages plants and reduces crop yield. The proposed level corresponds to levels of seasonal ozone exposure scientists have determined would be more protective.
EPA will seek public comment on the proposal for 90 days following publication in the Federal Register, and the agency plans to hold three public hearings. EPA will issue final ozone standards by Oct. 1, 2015.

More Resources:

EPA Ground Level Ozone site