LOS ANGELES – Los Angeles is once again America's smog capital, it was reported Nov. 14 by NBC 4 News. The city actually has had fewer smoggy days this year than last, continuing a relatively steady three-decade trend toward cleaner air, the Los Angeles Times reported. But Houston and California's San Joaquin Valley, which in recent years rivaled and even surpassed Los Angeles 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 air quality, the Times reported. 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, according to the Times. “It's a tough job cleaning up the ozone at this point because there are not a lot of easy emissions to target,” Joe Cassmassi, planning and rules manager for the South Coast Air Quality Management District, the region's chief smog-fighting agency, told the Times. “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.