California´s air quality improved substantially this year thanks to cooler weather.
The San Joaquin Valley had nine bad air days this year — compared with 36 at the same time a year ago.
That´s welcoming news after three years of worsening smog that´s made California the most polluted state in the country.
Last year, four Southern California counties surpassed a federal health standard for ozone for 64 days.
So far this year, the region has exceeded the standard on just 27 days.
Air quality officials say the data show that the hazy skies are not only a product of pollution but of weather conditions.
High temperatures cook the chemical stew of pollutants that form smog, resulting in high ozone levels.