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Autumn Parry / The Californian

Smog is seen in the air during sunset at the foot of the Grapevine in this file photo.

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Felix Adamo / The Californian

Smog settles in near the mountains south of Bakersfield in this photo taken from Comanche Drive looking to the southwest over oilfields and orchards.

Have you been feeling an uncomfortable tightness in your chest? Are your reaching for your asthma inhaler more often?

If so, the cause may be related to the valley's terrible, awful no-good air.

In summer, the valley's biggest air problem is ozone, an unhealthy component of smog that forms under the hot, summer sun.

But this time of year the valley's air pollution scourge is particulate matter, or PMs, a mixture of tiny solid particles and liquid droplets in the air. The size and composition of PM is directly linked to potential health hazards.

"The air quality has been unhealthy," said Jaime Holt, a spokeswoman for the San Joaquin Valley Air Pollution Control District.

"It's been a challenge for the last couple of weeks," she said, "due to these stagnant air patterns."

The valley's unusually mild, dry weather has allowed more particulates to become concentrated inside the valley's bowl-like topography, raising health concerns not only for sensitive groups but for healthy individuals as well.

Since Christmas Eve, PMs measured at a central Bakersfield station have spiked into the "very unhealthy" zone known as Level 5, a concentration of more than 75 micrograms of particulate matter per cubic meter of air.

The "good" zone, or Level 1, cannot show concentrations exceeding 12 micrograms of PM per cubic meter of air.

"People should be mindful about where they exercise," Holt said. "And don't use your fireplace."

Even at the "unhealthy" Level 4, which is 56 to 75 micrograms per cubic meter, sensitive individuals are advised to exercise indoors, and everyone should avoid prolonged or vigorous outdoor activities.

If you're trying to work off those extra holiday pounds, consider working out indoors.

Unlike summer, when the best air quality is typically found during the early-morning hours, it is reversed in winter. That's because when it gets cold overnight, the inversion layer, which acts like a lid atop the bowl, drops lower, squeezing the PM into a smaller space, and concentrating it even more.

Until the weather changes, we can look forward to more unhealthy air.

"We need a big storm," Holt said. "With rain, with wind, with low pressure."

But Brian Ochs, a meteorologist at the National Weather Service's Hanford station, said we'd better hunker down. There's no relief in sight.

"At least through next week we're not seeing much change," he said.

In fact, the chance of precipitation in the long-term forecast through January has been revised downward, he said.

"There's a somewhat more elevated chance of above-normal temperatures," Ochs said. "And the odds of below-normal precipitation in January is now 35 to 40 percent."