Residents of Visalia can't rely on summer winds and rains to wash away high ozone and particle pollution. On average, less than a third of an inch of rain falls between June 1 and September 30.
And since the city is located hard up against the Sierra foothills, air flowing eastward hits the mountains and stays there, building up pollutant levels.
Forest fires and smoke are a bigger problem here than elsewhere in the San Joaquin Valley. Visalia is close to national forests in the mountains and the U.S. Forest Service holds "prescribed burns" to keep the underbrush under control, according to Seyed Sadredin of the San Joaquin Valley Air Pollution Control District.
"Even worse, we have wild fires, which totally overwhelm the control in place," he said. In a particularly bad year, like 2008, he said, there can be 3,000 wildfires in the area.
