Pollution is spreading across the United States for the first time in 5 years

Driven by Canadian wildfires, pollution in the United States in 2023 was not only the highest it's been in the last decade, but also more geographically spread. As wildfire smoke expanded across Wisconsin, Illinois, Indiana, and Ohio, and even to Pennsylvania, Oklahoma, and as far south as Mississippi, many counties in these states became the top 10 most polluted for the first time since 2019—replacing counties in California, which typically dominate the list. This is not to say that pollution levels in California have reduced—they have remained fairly constant over the past two years. But it does indicate that air quality became a problem for many more states in 2023.

While average particulate pollution concentrations in the United States still remained just below the national standard, pollution rose 20 percent in just one year. At this level, the country could potentially gain 105.1 million total life years if air quality permanently met the WHO guideline. The backslide shows that even with stricter air quality standards and decades of strong enforcement, countries like the United States cannot escape the ghost of fossil fuels that are driving climate change.

See factsheet: United States