By 2050, some parts of the US, and especially California, the Southwest and the Northeast, could be experiencing up to 9 extra days a year of unhealthy ozone levels, unless emissions are brought under control. This is the conclusion of research published in Geophysical Research Letters.

Other regions are likely to see an additional 2.3 days on average of dangerous ozone levels, with accompanying increases in respiratory illness, exacerbating the health risks for children, seniors and those prone to asthma.

Tropospheric, or “bad,” ozone results when pollutants emitted by cars and industry react in the presence of sunlight. Tropospheric ozone is the main ingredient in smog.

Short-term exposure to ozone is associated with adverse health effects, and high ozone levels can worsen chronic lung disease, potentially leading to fatalities.