El Centro's air quality has several factors working against it, namely its hot, dry climate and the border it shares with Mexico, which has much less stringent clean air laws, according to Brad Poiriez, air pollution control officer for the region.
The city tries to keep dirt roads and farm drives watered or covered with crushed asphalt to stop dust from flying, but there's still plenty of open land where strong winds can stir it up.
The steady stream of traffic to and from Mexico only makes it worse. Often the line is more than two hours long, which means cars idle in the hot desert sun and emit a steady stream of exhaust, said Poiriez. Many of those cars are registered in Mexico and are older models with engines that burn dirtier than newer cars.
The air pollution control office has been working with Mexican authorities to require vehicles that cross the border to meet U.S. emissions standards. It has also gotten Mexican authorities to limit uncontrolled burns on farms. That helped the area reduce its pollution in 2012, but it still has a way to go.
