http://www.sciencemag.org/news/2019/04/drought-not-just-about-water-it-affects-air-pollution-too

A lengthy California drought left trees and plants parched and influenced their contributions to smog.

The severe drought that struck California from 2011 to 2015 had an obvious impact on rivers, forests, and wildlife. Now, a new study shows it also had some surprising effects on the state’s notorious air pollution, adding new wrinkles to the state’s efforts to clear the skies.