Southern California has enacted the strictest air-quality requirements in the nation, including most of Los Angeles, Orange, San Bernardino and Riverside counties. Cars are cleaner. Businesses have new rules to reduce emissions. And there are new standards to clean up diesel engines in trucks on the highway and ships in the port. Nonetheless, the region is still the king of smog, ahead of the San Joaquin Valley, with 67 unhealthy ozone days, and Houston, with 24. The smog season begins May 1 and ends Oct. 31. Advocates for cleaner air said it’s up to each resident to help cut smog. “We can’t say it enough: We’re all responsible for that air we breathe in L.A.,” said Julia Robinson Shimizu, spokeswoman for Breathe California of Los Angeles County. That means each resident can use cleaner cars. Drive less. Take the train or bus. Walk. Burn less energy. And support legislation to help clean the air, she said. “The only way we’re going to solve the traffic and resulting pollution is to implement more mass transit. The Orange Line is fabulous,” said Robinson Shimizu, who lives in the San Fernando Valley. “I have been breathing deeply each day this year, and I am so glad that every year gets a little bit easier.” [email protected] (818) 713-3730160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! Breathe deeper – but not too deeply: The nation’s most smog-choked city is poised for its cleanest year on record. Los Angeles, the smoggiest city in the nation for four years running, recorded 78 unhealthy ozone days through Monday, its fewest for a year since 1976. With clean air expected through the end of smog season, Oct. 31, the Southland will likely set a healthy-air record, air regulators said Tuesday. “We are headed in the right direction toward our goal of clean air,” said William A. Burke, governing board chairman for the South Coast Air Quality Management District. “The challenge ahead will be to maintain and increase our momentum, especially in cleaning up construction equipment, trucks, trains, ships and the ports.” In 1976, Angelenos breathed amidst more than 200 unhealthy ozone days lasting at least eight hours at an average of 0.08 parts per million, the federal standard. Since then, clean-air laws have cut those numbers more than in half. The last Stage III smog alert was in 1974, when ozone hit 0.51 parts per million. The last Stage I alert was in 2003. The next year, the Southland suffered 88 unhealthy ozone days; then it had 84 days in 2005 and 86 during last year’s record hot summer. Regulators attribute this year’s low to an unseasonably cool summer, with an eight-hour ozone low of 0.137 ppm, the lowest concentration on record. “The air-quality improvement is due to forging ahead on all fronts to reduce pollution,” AQMD spokesman Sam Atwood said.