In addition to checking the temperature and the chance of rain before leaving home, many people have been forced to add a new indicator to their daily weather check – air quality.
Ground-level ozone pollution – more commonly known as smog – reached dangerous levels across the U.S. this summer. EDF’s new analysis found that almost every state experienced unhealthy levels of it, with millions of Americans exposed to dangerous air pollution.
The current national standard for ground-level ozone pollution is 70 parts per billion. As you can see from the maps above, 45 states had at least one day between March and August with levels that exceeded that limit.
However, there is a substantial and growing body of scientific evidence that shows serious health effects from ground-level ozone exposure at levels below the current standard. When the data is expanded to consider ground-level ozone levels greater than 60 parts per billion, which would be a health-based standard more consistent with the scientific evidence, the picture of summer ozone levels is even more concerning – all but one state (Hawaii) had at least one day with levels that exceeded that amount.
Our analysis also found:
- The Western U.S. experienced the worst ozone levels in the country this summer. California, Arizona and Colorado experienced the most high-ozone days between March and August.
- 343 counties recorded at least one high-ozone day. San Bernardino, California recorded the most exceedances – 112 high-ozone days between March and August, including almost every day in July and August.
- More than 31 million people live in the 24 counties that had more than 20 high-ozone days between March and August, including Denver County in Colorado, Maricopa County in Arizona, and Los Angeles County in California.
- If you use the more health-protective standard of 60 parts per billion, a majority of days between March and April had unhealthy ozone levels across the Western U.S.
- In Arizona, under the 60 parts per billion standard, 89% of days between March and August had unhealthy ozone levels somewhere in the state.
There were many wildfires this summer and wildfire smoke is one of the sources that can contribute to elevated levels of ozone pollution. EPA establishes standards based on health science alone, and the agency has long had policies in place that allow states to account for truly exceptional events. Our analysis includes all recorded high ozone readings and does not exclude any high ozone days
