Haze at sunset isn’t wildfire smoke, so what is it?

Have you noticed the haze out over the horizon this week during the sweltering heat? It turns out it’s not the wildfire smoke more typical in August than June.

Seattle area’s ‘insane’ heat wave finally gives way to cooler weather

The Washington State Department of Ecology says it’s actually Secondary Organic Aerosols (SOA). Even trees emit terpenes and isoprene gases more so on hot days, the Ecology department explained in its blog. They’re “secondary” because the aerosols form as a result of processes happening in the atmosphere.

Those emissions are just some of the ingredients in what makes up smog formation.

“They react with oxides of nitrogen (mostly from traffic and industrial sources) under the right meteorological conditions to form ozone,” the Ecology department writes.

According to the blog, the extreme heat pushes air downward and traps pollutants in a shallow layer of the atmosphere, also known as a subsidence inversion.

The mixture of all those elements came together and result in high levels of ozone, which makes for some incredible sunsets. However, it can be unhealthy for sensitive groups.

On Tuesday, the air quality remains Good to Moderate across most of Western Washington. Check here for updates.

The bad news is that the aerosols will push air quality in parts of the Puget Sound region today into the "unhealthy for sensitive groups" range, or even into the "unhealthy" category. The good news is that air quality should improve as the temperatures dip on Tuesday.

— WA Department of Ecology (@EcologyWA) June 28, 2021

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