Heat Brings Foul Air

After a long, cool spring, a weeklong siege of smog has gripped inland valleys from Simi Valley to San Bernardino, bringing warnings that afternoon air is dangerous for most everyone to inhale.

Thursday marked the seventh consecutive day when ozone, a main ingredient in smog, reached the unhealthful mark in at least one location in the Los Angeles region.

Crestline, the hamlet in the San Bernardino Mountains that, by a quirk of nature, has become the region’s smog magnet, is getting the worst of it. But other cities are feeling the early sting of air pollution, including Palm Springs, Riverside, Fontana, Redlands, Lake Arrowhead, Pasadena, Santa Clarita and Glendora.

This week’s bout of bad air marked the earliest arrival of so much smog in several years. Blame triple-digit temperatures and a stubborn inversion -- a warm-air layer that traps smog over valleys like a trash can lid -- say air quality regulators.

The sudden bad air quality, officials say, is a reminder that although Southern California’s smog has been steadily lessening in both frequency and intensity, the region’s potent mix of sunshine, mountains, millions of people and their cars can still deliver heavy doses of dangerous pollution to residents, particularly in inland regions.

A decade ago, a temperature inversion like the current one would have triggered days of extremely unhealthful air quality, conditions when simply walking out the front door would have caused even healthy adults to suffer headaches, teary eyes and wheezing, said Sam Atwood, spokesman for the South Coast Air Quality Management District.

Schools in inland districts used to frequently keep children inside for recess and gym class to avoid smog. Now, that happens only once or twice a year, said Linda Hill, a spokeswoman for the San Bernardino City Unified School District.

Extremely unhealthful levels of ozone have not been seen anywhere in the region since 1998. But “even though we’re no longer seeing Stage 1 episodes, it is still quite noticeable when the ozone is unhealthful,” Atwood said.

“In the Inland Empire, there’s been a very noticeable degradation of visibility and hazy conditions. It’s a reminder everyone should keep their eyes on the air quality forecast to adjust their activities accordingly,” he said.

Ozone is a colorless, poisonous gas. It can scar lung tissue, not to mention paint, metal and rubber. Symptoms of ozone exposure include headaches, nausea and shortness of breath. Long-term health effects include loss of lung function. Other pollutants, such as smoke, dust, soot and nitrates, form haze that gives the sky a gauzy appearance.

Through much of the spring, the smog had been kept at bay by prolonged cool, moist weather brought here by a weak El Nino system, said Joe Cassmassi, senior meteorologist for the AQMD.

But this week, those conditions were replaced by warm, sunny weather perfect for ozone, which is created in the atmosphere when man-made emissions mix together in sunlight. Meanwhile, sea breezes and coastal fog have been too weak to dissipate the smog.

“This is a little bit of surge for this early in the year. There’s just a very stagnant weather pattern with a strengthening inversion,” he said. “It just builds up each day.”

Cooler temperatures, coastal fog and mild sea breezes should arrive to break the smog stranglehold for the Memorial Day weekend. But the respite will be brief, Cassmassi predicted, with ozone due to return next week.

Summer smog should be no worse than last year, he said. On the other hand, last year was worse than the previous couple of years.

About the only smog-free place is along the coast. Indeed. plotting ozone across the Southern California map increasingly resembles an election-night map, divided between blue cities to the west and smoggy, red cities inland.

Marilynn Morris moved to the clear skies of Canyon Lake after four decades in smoggy Riverside, a move for which she is thankful.

“I’m glad I left here, especially on days like this,” she said Thursday during a visit to downtown Riverside. She said she could sense the smog in her nose and lungs as she returned to the city yesterday. “I can tell, definitely,” she said.

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Times staff writer Seema Mehta contributed to this report.