With a little help from good weather, air in the Los Angeles was the cleanest on record this year, regulators said on Nov. 4, according to the Associated Press. Still, the region's air quality remained the worst in the nation by one key measure, said Sam Atwood, a spokesman for the South Coast Air Quality Management District. "The weather was a major factor this year, there's no denying that," Atwood said. "We're headed in the right direction but we have to definitely not rest on our laurels." Southern California, which has struggled with air pollution for half a century, historically has its worst smog between May 1 and Oct. 31. The region benefited this year from weather that isn't conducive to smog, including cooler temperatures, fog, low clouds and weak inversion layers. Cleaner cars, industries and businesses also improved air quality, officials said. This year, there were only 27 days during that period when the region's ozone level, averaged over one hour, exceeded the federal Environmental Protection Agency's standard. Overall, the region violated the one-hour standard 68 days last year, officials said. Ground-level ozone, a precursor to smog, causes respiratory illnesses that can be especially harmful to the elderly, children and people with asthma. The Los Angeles area still had the highest peak level of ozone averaged over an eight-hour period - a newer, stricter EPA measure than the one-hour standard.