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Why Is The Air Quality In LA So Much Worse Today?

The afternoon sun between palm trees in Arcadia (Frederic J. Brown/AFP via Getty Images)
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Even though much of California was blanketed in smoke yesterday, the Los Angeles area appeared to have pretty good air quality, at least according to sensors.

However, this morning people woke up to their lungs burning as smoke penetrated homes. The sensors read red or even purple, as dangerous levels of the Air Quality Index was reached.

What happened?


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Our skies are mostly grey because of the massive amount of smoke and ash flowing down from the fires in Northern California.

Though, that didn’t necessarily translate into poor air quality in L.A.

Some of these fires are so large that they inject burning matter tens of thousands of feet into the atmosphere. Up there, smoke and ash can get pushed by winds high up in the atmosphere, traveling some time before touching down.

“It’s possible that they’re impacting air quality, just not on the local area,” said Michael Jerrett, Professor of Environmental Health Science at UCLA.

"With some of these mega wildfire complexes, you actually start seeing them affecting air quality literally thousands of miles away,” said Jerrett. “They could potentially have impacts on the Great Lakes, all of the way from California.”

Just because air quality monitors said everything was OK yesterday, ash from the fires was still falling across many parts of Southern California. Unsurprisingly, ash is not healthy to breathe, but it doesn’t factor into air quality measurements.

“Our monitors aren’t designed to pick up ash. They’re designed to pick up the smaller particles which is sort of our typical urban air pollution concern,” said Philip Fine, Deputy Executive Officer at the South Coast Air Quality Management District.


So why is the air quality so bad today? Growing and shifting winds at the local level.

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Places like Pasadena, Monrovia, and even Downtown Los Angeles, are being choked by smoke because of the Bobcat Fire burning nearby.

Yesterday, some of that smoke was likely dissipated by the Santa Ana wind event that blew through. Today, there are light winds coming from the East and North East, pushing smoke from the fire over the San Gabriel Valley.

Same goes for San Bernardino and the El Dorado Fire.

“It could be a little smokey because we’re not expecting much in the way of wind the next few days,” said David Sweet, meteorologist with the National Weather Service.

Interestingly enough, the smoke is likely impacting temperatures as well.

Sweet said that it’s about 10-15 degrees cooler today than yesterday, in part because the thick blanket of smoke is keeping the sun’s rays from reaching the Earth’s surface. The lack of onshore winds is also playing a major part.


Whether you’re inundated with smoke over the next few days will depend on whether or not firefighters are able to get a handle on the Bobcat and El Dorado fires. And whether the wind blows your way.

Remember, if you smell smoke or see ash falling, it’s best to stay inside.

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