Smog: A Bane for All Seasons in the San Gabriel Valley

Don’t adjust your calendar. Just because it looks as if it’s August out there doesn’t mean the summer smog season has arrived early in the San Gabriel Valley.

No, this is the winter smog season, when nitrous dioxide often dominates the air and makes it look brown.

Winter smog is not uncommon, and is created when foggy mornings collaborate with excessive amounts of nitrous dioxide and contaminants from automobiles, trucks, buses and dust, air quality officials say.

The result is a low-lying haze that does no favors to the lungs. It can impair breathing and makes the sight of the peaks of the San Gabriel Mountains nothing more than a fond memory.

But Claudia Keith, a spokeswoman for the South Coast Air Quality Management District, said: “I don’t think we’re having anything out of the ordinary. It’s just your typical winter smog going into springtime.”

The good news, she said, is that in winter “when we don’t have as much sunlight . . . there isn’t as much of an opportunity for the formation of ozone.” Ozone, though invisible, is the most dangerous of smog’s components.

The murky look these days probably comes from elements known as “10 micron particulates,” minuscule but abundant contaminants made up of everything from debris of radial tires to diesel fuel residue and soot. “When you can’t see the mountains, it’s usually because of particulates,” Keith said.

The main source of particulates remains constant, winter or summer, she said: “The main culprit is the car.”

Even though it looks bad out there, it’s not nearly as smoggy as in the summer, Keith said. “We have moderate levels of pollutants in the air now, regardless of what you see. And we haven’t had any smog alerts.”

So far, the worst day in recent weeks for the San Gabriel Valley was Feb. 5, Keith said. On that day, the air quality district’s recording station in Pomona indicated an officially “unhealthful” reading of 140 on the Pollutant Standard Index, a scale for measuring the intensity of air contamination.

On the scale, 0-50 is considered good; 51-100, moderate; 101-200, unhealthful; 201-275, very unhealthful, and above 275, hazardous.

Smog alerts are declared when the reading is 200-plus, Keith said. Those usually start kicking in after the official start of the summer smog season--May 1.