The same stagnant air that has, with ruthless efficiency, kept the rain out of California has kept the pollution in. The drought has turned the wooded mountains that surround the San Joaquin Valley’s farmland into kindling. The 2015 wildfire season was the most destructive on record, with fires so big and fast-moving that they’ve been dubbed “super fires.” As the fires blazed along the western edge of the Sierra Nevada, smoke and ash poured downwind into the valley. Fresno saw what Bonnie Holmes-Gen, senior director for air quality and climate change for the American Lung Association, called “nightmare scenarios.”