Fresno's air suffered a setback last year, with an increase in the particle pollutants found in smoke and haze like soot and sulfur dioxide, which can aggravate asthma and heart issues.
The Fresno metro area's population sharply increased 16% between 2000 and 2010, spurring the once compact city to sprawl outwards. Now, residents drive much further distances to get to work, leaving a trail of exhaust and emissions.
"Air pollution is proportional to vehicular traffic," said John Swanton, an air pollution specialist with the California Air Resources Board.
Like other cities located in California's valleys, layers of warm air trap those emissions like a lid on a cooking pot and pollution builds up to unhealthy levels.
