The US Environmental Protection Agency (EPA) is proposing to retain, without changes, the existing, more stringent 2015 National Ambient Air Quality Standards (NAAQS) for ozone. The standards, established in 2015, are currently set at 70 parts per billion (ppb), in terms of a 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentrations.

From 2017 to 2019, ozone concentrations fell 4%. Since the beginning of the Trump Administration, EPA has also re-designated 13 nonattainment areas for the 2008 8-hour ozone standards to attainment meaning these communities are now breathing cleaner air.

A majority of EPA’s science advisors, the Clean Air Science Advisory Committee (CASAC), recommended the agency retain the primary standard, and reached consensus to recommend EPA retain the secondary standard.

As a result of Clean Air Act programs and efforts by state, local, and tribal governments, from 1990-2019, US emissions of nitrogen oxides and volatile organic compounds have dropped by 65% and 47% respectively. During that same time, national average ozone concentrations have dropped 25%.

EPA will accept comment on this proposed decision for 45 days after it is published in the Federal Register.

Background. The Clean Air Act requires EPA to set NAAQS for criteria pollutants. Currently, ozone (and related photochemical oxidants) and five other major pollutants are listed as criteria pollutants. The law requires EPA periodically to review the relevant scientific information and the standards and revise them, if appropriate, to ensure that the standards provide the requisite protection for public health and welfare.

In the prior review of the ozone standards, which was completed in 2015, EPA increased the stringency of the levels of the ozone standards to 70 parts per billion (ppb), from the 2008 standard of 75 ppb.

EPA said it is focused on reviewing the NAAQS within the Clean Air Act 5-year time frame because of the potentially significant impacts of a NAAQS revision on economic activity, state agency planning resources, public health, and the environment.