Southern California Air Quality Takes a Turn for the Worse

After years of gradual improvement, Southern California’s air quality took a tumble this summer, falling to its worst levels since 1997 due to the combined effects of hot weather and increasing emissions. Taken as a whole, the region’s air quality has dramatically improved in the last quarter-century, but the rising smog levels in the last three years, and especially this past summer, threaten that long-term trend. Southern California had 30 percent more smoggy days this summer than last, and twice as many smoggy days as Houston, usually a close competitor in the terrible-air contest. Vehicle emissions in the famously car-clogged region are the primary cause of the problem, followed by household chemicals (such as cleansers and hair spray), factory emissions, and diesel engines.