Fresno's Air: The Valley That Traps Everything
Near Fresno, California
Fresno is surrounded by mountains. The Sierra Nevada rises to the east. The Coast Ranges close in from the west. The Tehachapi Mountains form a wall to the south. This geography, which in promotional materials is described as scenic, is also a bowl. And a bowl collects what falls into it.
The San Joaquin Valley air quality problem is not a recent discovery. The valley floor has been accumulating particulates since the agricultural and industrial economy of the twentieth century began generating them in quantity. Diesel exhaust from the trucks and farm equipment that move the valley's harvest through its roads and highways. Dust from tilled fields, from gravel pits, from construction sites. Agricultural burning, which was used for decades to clear fields after harvest and which produces smoke that settles on the valley floor when the atmospheric inversion layer, a warm-air lid that forms above the basin in certain conditions, prevents it from rising and dispersing. Wood smoke from residential heating in communities that cannot afford alternative fuel. All of it collects in the bowl.
The San Joaquin Valley Air Pollution Control District was established to address the problem, and the valley has made measurable progress in some categories of air pollutants. It has not solved the problem. As of the most recent available data, Fresno County consistently ranks among the most polluted counties in the United States by measures of both particulate matter and ozone concentrations. The American Lung Association has placed Fresno on its most-polluted cities list repeatedly. Asthma is a serious concern for children in the valley.
The communities most exposed to the worst air are not the communities with the most economic or political power to change it. The farm labor communities of the valley floor, many of them Latino, bear the highest exposure to diesel exhaust from the truck routes and agricultural machinery. The atmospheric geography that makes the valley valuable for farming, the sheltered basin with reliable sun and deep soils, is also the geography that makes it hard to breathe.
