Air quality on the PNW coast shows as poor, with seemingly no reason

I have a sensor right on the coast in Long Beach Washington, my sensor very often relays that PM2.5 is moderate to unhealthy. This seems to be the case for other sensors located along the Oregon coast.
The thing is, that there doesn’t appear to be any reason for the air quality to be poor, the wind is straight off the Pacific ocean, there is no sand storm, no fires, seemingly no pollution.
And sensors that are situation just inland will often show much better air quality.
Any ideas about what could be causing the PM2.5 to be showing such high readings and should we consider the air quality harmful when there doesn’t seem to be a clear reason for it?

My sensor is about 1-1/4 miles from the beach in Hawaii. I have noticed during periods of stronger (20 MPH+) onshore wind conditions that my sensor and others in similar near-shore locations here record higher 2.5u readings.

According to

“the size of sea salt aerosols ranges widely from ~0.05 to 10 μm in diameter”

I’m not a scientist, but I suspect what your (and my) device is measuring is sea salt aerosols carried by onshore winds.


I regularly see this same thing on the Oregon coast. It’s one of a few phenomena I haven’t been able to explain very well. This explanation makes a lot of sense – thanks for offering it.

Notably, Astoria is almost always shielded from this effect. It sits 4-5 miles off the coastline, along the Columbia.

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