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How can we have moderate air quality and an Air Quality Alert at the same time?

Why air pollution monitors aren't picking up smoke
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Posted at 10:54 AM, Oct 16, 2017
and last updated 2017-10-16 14:35:27-04

It's been a terrible two weeks for air quality in the Central Valley. Kern County has been under an Air Quality Alert (also known as an Air Quality Warning) due to wildfire smoke coming down from the Lion Fire in the Sequoia National Forest and the complex fires burning in the Napa Valley region.

But that has caused confusion for many residents, because the San Joaquin Valley Air Pollution Control District has been measuring the air quality and most of the time that we've been under that Air Quality Alert, the actual measurement of pollution here in the south valley is in the moderate range. That's a clear discrepancy because we all know moderate air quality doesn't look and feel this bad, especially not when we can clearly smell the smoke and see the thick haze on the horizon.

Anna Stone, Outreach and Communications Representative with the Valley Air District, explains that the problem is two-fold:

First, wildfire smoke tends to fill into the valley, foothills and mountains in pockets. So while they have approximately 30 measurement sites around the valley measuring the pollution, the sites may simply just be missing the smoke.

The second problem is the equipment is designed to measure particulate pollution, which is microscopic, and smoke particles tend to be much larger. So the measuring sites simply can't pick up the smoke even if there is a pocket overhead.

So which do you believe, the air quality rating that says we are in the moderate range, or the Air Quality Alert that says the air quality is unhealthy and people should take precautions?

When in doubt, trust the Air Quality Alert, which is issued by the National Weather Service, but the meteorologists there have consulted with the pollution officials. Even the Valley Air District's site gives that recommendation here:

Please note: If you can smell smoke and see ash, that is an indication that you should be treating air quality conditions as a RAAN Level 4 or higher. The District’s RAAN monitors are designed to detect the fine particulates (called PM 2.5 which are microscopic in size and not visible to the human eye) that exist in wildfire smoke. Ash particles are much larger in size and will not be detected by our monitors. Therefore your area may be covered in ash, while our PM monitor reflects a moderate reading.

A Level 4 means the air is unhealthy for everyone, not just sensitive groups.

So what should you do when the air quality is unhealthy? Seniors and young children are considered the most at risk with sensitive lungs, and they should stay indoors. But even healthy active adults should limit outdoor exposure and avoid overexerting themselves in this bad air quality.

Thankfully it looks like there's an end in sight! The forecast brings a rush of clean air from the northwest at the end of this week with a significant cold front. Fire crews have made significant ground on the fires burning across the state, so if they can gain more containment over the next several days, we shouldn't see as much smoke filling into Kern County and we'll have a better weekend ahead. Click here to see the rest of the forecast, including a chance of rain!

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