The US Environmental Protection Agency (EPA) its revising the National Ambient Air Quality Standards (NAAQS) for ground-level ozone to 70 parts per billion (ppb) from 75 ppb to protect public health. Ground-level ozone forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the air.
EPA examined nearly 2,300 studies in this review of the ozone standards including more than 1,000 new studies published since the last review of the standards in 2008. Scientific evidence shows that ozone can cause a number of harmful effects on the respiratory system, including difficulty breathing and inflammation of the airways. EPA estimates that the public health benefits of the updated standards will range from $2.9 to $5.9 billion annually in 2025 (outside of California), outweighing the estimated annual costs of $1.4 billion.
These annual benefits include the value of avoiding a range of harmful health effects, including:
- 320 to 660 premature deaths
- 230,000 asthma attacks in children
- 160,000 days when kids miss school
- 28,000 missed work days
- 630 asthma-related emergency room visits
- 340 cases of acute bronchitis in children
EPA analyzed the benefits and costs for California separately, because a number of areas in California would have longer to meet the final standards, based on their ozone levels. A number of California counties likely would have attainment dates ranging from 2032 to late 2037.
Benefits of meeting the standards in California add to the nationwide benefits after 2025, with the value of the additional benefits estimated at $1.2 to $2.1 billion annually after 2025. This includes the value of avoiding harmful health effects, including:
- 120 to 220 premature deaths
- 160,000 asthma attacks in children
- 120,000 days when kids miss school
- 5,300 missed work days
- 380 asthma-related emergency room visits
- 64 cases of acute bronchitis in children
Estimated costs in California post-2025 are $800 million. Estimated net benefits range from $1.5 to $4.5 billion nationwide, except California. In California, net benefits are estimated at $0.4 to $1.3 billion.
Some health advocates, such as the , expressed concern that the new rules are not stringent enough.
EPA addressed this by stating that while several clinical studies have shown effects in some adults following exposure to ozone at levels as low as 60 ppb, the evidence is uncertain that those effects are harmful or “adverse.” In light of these uncertainties, the EPA Administrator concluded that the science supported setting a standard that reduces exposure to ozone concentrations as low as 60 ppb but does not support a standard that eliminates them.
The Administrator concluded that a standard of 70 ppb also will provide the adequate margin of safety the law requires. The updated standard will protect more than 98 percent of school-age children from repeated exposures to ozone concentrations as low as 60 ppb—a 60 percent improvement over the current standard.
Local communities, states, and the federal government have made substantial progress in reducing ground-level ozone. Nationally, from 1980 to 2014, average ozone levels have fallen 33%, while the economy has continued to grow. EPA projects that by 2025, existing rules and programs will bring the vast majority of the remaining counties into compliance.
Advances in pollution control technology for vehicles and industry along with other emission reduction standards, including “Tier 3” clean vehicle and fuels standards, the Clean Power Plan and the Mercury and Air Toxics Standards, will significantly cut smog-forming emissions, helping states meet the updated ozone standards.
To ensure that people are alerted when ozone reaches unhealthy levels, EPA is extending the ozone monitoring season for 32 states and the District of Columbia. This is particularly important for at-risk groups, including children and people with asthma because it will provide information so families can take steps to protect their health on smoggy days.
EPA also is strengthening the “secondary ozone standard” to 70 ppb, which will improve protection for trees, plants and ecosystems. New studies since the last review of the standards add to evidence showing that repeated exposure to ozone reduces growth and has other harmful effects on plants and trees. These types of effects have the potential to harm ecosystems and the benefits they provide.
The Clean Air Act provides states with time to meet the standards. Depending on the severity of their ozone problem, areas would have until between 2020 and 2037 to meet the standards.