|Counties where measured ozone is above proposed range of standards, based on 2011-2013 monitoring data. Source: EPA. Click to enlarge.|
The US Environmental Protection Agency (EPA) is proposing tightening the ground-level 8-hour ozone (O3) National Ambient Air Quality Standards (NAAQS) to within a range of 65 to 70 parts per billion (ppb), while taking comments on a level as low as 60 ppb. Earlier this year, EPA staff had recommended the further reduction of this primary ozone standard from the current 75 ppb (parts per billion) to a revised level within the range of 70 ppb to 60 ppb—and preferably below 70 ppb. (Earlier post.)
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 1 October 2015.
The Clean Air Act established two types of national air quality standards:
Primary standards set limits to protect public health, including the health of at-risk populations such as people with pre-existing heart or lung disease (such as asthmatics), children, and older adults.
Secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings.
The Clean Air Act requires EPA to review the standards every five years by following a set of open, transparent steps and considering the advice of a panel of independent experts. EPA last updated these standards in 2008, setting them at 75 ppb.
EPA 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 still pose serious threats to public health, harm the respiratory system, cause or aggravate asthma and other lung diseases, and is linked to premature death from respiratory and cardiovascular causes.
Ground-level ozone forms in the atmosphere when emissions of nitrogen oxides and volatile organic compounds “cook” in the sun from sources such as cars, trucks, buses, industries, power plants and certain fumes from fuels, solvents and paints. People most at risk from breathing air containing ozone include people with asthma, children, older adults, and those who are active or work outside. Stronger ozone standards will also provide an added measure of protection for low income and minority families who are more likely to suffer from asthma or to live in communities that are overburdened by pollution. Nationally, 1 in 10 children has been diagnosed with asthma.
According to EPA’s analysis, strengthening the standard to a range of 65 to 70 ppb will provide significantly better protection for children, preventing from 320,000 to 960,000 asthma attacks and from 330,000 to 1 million missed school days. Strengthening the standard to a range of 70 to 65 ppb would better protect both children and adults by preventing more than 750 to 4,300 premature deaths; 1,400 to 4,300 asthma-related emergency room visits; and 65,000 to 180,000 missed workdays.
Costs are estimated at $3.9 billion in 2025 at a standard of 70 ppb, and $15 billion at a standard at 65 ppb nationwide, excluding California. EPA has analyzed costs and benefits for California separately, because a number of California counties would have longer to meet the proposed standard, based on their ozone levels. A number of California counties likely would have attainment dates ranging from 2032 to late 2037.
Estimated costs of meeting the proposed standards in California post-2025 are $800 million for a standard of 70 ppb, and $1.6 billion for a standard of 65 ppb.
EPA estimates gained health benefits of $6.4 to $13 billion annually for a standard of 70 ppb, and $19 to $38 billion annually for a standard of 65 ppb, except for California, factoring in an estimated:
- 750 to 4,300 premature deaths;
- 790 to 2,300 cases of acute bronchitis in children;
- 1,400 to 4,300 asthma-related emergency room visits;
- 320,000 to 960,000 asthma attacks in children;
- 65,000 to 180,000 days when people miss work; and
330,000 to 1 million days when children miss school.
Benefits of meeting the proposed standards in California add to the nationwide benefits after 2025, with the value of the additional benefits ranging from an estimated $1.1 to $2 billion at a standard of 70 ppb to $2.2 to $4.1 billion for a standard of 65 ppb.
A combination of recently finalized or proposed air pollution rules—including “the Tier 3 clean vehicle and fuels standards (earlier post)—will cut smog-forming emissions from industry and transportation, helping states meet the proposed standards, EPA suggested.
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 vast majority of US counties with monitors would meet the more protective standards by 2025 just with the rules and programs now in place or underway. Local communities, states, and the federal government have made substantial progress in reducing ground-level ozone. Nationally, from 1980 to 2013, average ozone levels have fallen 33%. 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.
Secondary standard. EPA is proposing to define the secondary standard in terms of a “W126 index” in a range of 13 to 17 parts per million-hours (ppm-hours), averaged over three years. A “W126 index,” named for the formula used to calculate it, is a seasonal index often used to assess the impact of ozone on ecosystems and vegetation.
To achieve a level of protection equivalent to 13 to 17 ppm-hours based on the W126 metric, EPA is proposing to set an 8-hour secondary standard at a level within the range of 65 to 70 ppb. EPA analyzed data from air quality monitors and found that setting a standard in a W126 form would not provide additional protection beyond an 8-hour standard.
EPAis seeking comment on setting the standard based on the W126 metric within a range of 13 to 17 ppm-hours, averaged over three years. EPA also is seeking comment on defining a target protection level in terms of a W126 index value as low as 7 to 13 ppm-hours. In addition, EPA is taking comment on retaining the existing 8-hour secondary standard.