Los Angeles is America's smog capital once again.
The megalopolis actually has had fewer smoggy days this year than last, continuing a relatively steady three-decade trend toward cleaner air. However, Houston and California's San Joaquin Valley, which in recent years rivaled and even surpassed L.A. as the smoggiest areas in the country, experienced exceptionally clean air this year.
As a result, the Greater Los Angeles region is again home to the worst smog in the nation, according to the federal Environmental Protection Agency's latest barometer for measuring the unhealthful haze -- a dubious distinction the region has held for most of the last half-century.
Air quality in Los Angeles, Orange, Riverside and San Bernardino counties has exceeded the federal health standard for more than 2 1/2 months this year.
"It's a tough job cleaning up the ozone at this point because there are not a lot of easy emissions to target," said Joe Cassmassi, planning and rules manager for the South Coast Air Quality Management District, the region's chief smog-fighting agency. "The low-hanging fruit, as a lot of people like to say, has been taken."
Ground-level ozone, the primary ingredient in smog, is formed when two types of air pollution react chemically while being cooked by the sun's rays. Both of the pollutants, volatile organic compounds and nitrogen oxides, are emitted during the burning of fossil fuels in cars, factories and power plants.
Scientists have linked breathing smoggy air to an array of health effects, including wheezing and coughing because of irritated lungs, increased asthma attacks, reduced lung power and even premature death.
The South Coast Air Basin, which includes all of Orange County and most of the urbanized parts of Los Angeles, Riverside and San Bernardino counties, exceeded the EPA's smog standard on 84 days this year.
Last year, the region exceeded the standard on 90 days, and in 2003, it surpassed it on 120 days. The standard limits airborne concentrations of smog, or ground-level ozone, to .08 parts per million over an eight-hour period.
By comparison, the San Joaquin Valley, which in recent years had been the nation's biggest violator of the eight-hour standard, exceeded it on just 72 days this year -- the fewest ever since regulators began recording smoggy days. The region surpassed the mark on 109 days last year and 134 days in 2003.
"We'd like to believe that public awareness of this issue has become so high in the valley that people are changing their behavior," said Kelly Hogan Malay, a spokeswoman for the San Joaquin Valley Air Pollution Control District. She said the weather in the San Joaquin Valley was unusually hot for parts of this year, which should have created more smog.
Because the smog season tends to peak in summer and tail off after October, the totals for this time of year have traditionally been the final numbers.
The EPA requires areas that exceed the smog standard to develop plans to reduce ozone-forming pollution. Regions have different deadlines to meet the standard, based on the severity of their smog problems. If Los Angeles still exceeds the standard by 2021, it risks losing federal transportation funding.
Before adopting the eight-hour smog standard this summer, the EPA's dirty air barometer was a measure that limited concentrations of ozone over a one-hour period.
Though the eight-hour baseline is generally seen as a more accurate measure of smog levels, critics condemned the agency for pushing back the compliance deadline, which had been 2010 for Los Angeles, when it switched standards, arguing that it removed pressure on local officials to clean the air or lose federal money.
EPA officials said last week that the criticism was unjustified, arguing that their new rules still called for areas with smog problems to continue trying to meet the old one-hour standard, even if the actual regulatory deadlines had changed.
If the one-hour standard were still used, Houston would have topped Los Angeles as the nation's smog capital. Houston violated the one-hour standard on 33 days this year, compared with 30 days in the L.A. region.
Texas officials said they took no comfort in ceding first place in the annual smog derby to Los Angeles. They said they are tightening restrictions on air pollution in the Houston area, which largely stems from the cluster of oil refineries and chemical plants near the city.
"It's easy to say that we don't want to be No. 1 when it comes to smog. But we don't want to have the first-, the second- or the third-highest number of 'exceedences,' " said John Steib, deputy director in charge of enforcement and compliance for the Texas Commission on Environmental Quality.
Although the Los Angeles region once again finds itself leading the nation in smoggy air, state and local regulators have made dramatic strides in reducing the haze.