Scientists from the National Center for Atmospheric Research in Colorado released a study which said that the wildfires that hit California in September and October last year caused a rise in ozone levels.

Over 9,000 blazes burned more than one million acres of forest land and more than 2,000 houses in California.

According to NCAR lead scientist Gabriele Pfister, residents of rural regions far from the wildfires are still affected by the smoke. Pfister identified the areas where unhealthy air are concentrated as Kern, Tulare, El Dorado and Mariposa counties.

The NCAR study was published in the Geophysical Research Letters journal.