Chemistry of the orange sky

September 11, 2020

Orange sky at the College

Image: Looking toward Tan Kah Kee Hall (l) and Campbell Hall (r) from the mining circle (9/9/20). Photo by Pete Rosos for Berkeleyside

This event happened on September 9th, 2020.

The sky is orange because longer wavelength light (reds and oranges) are able to push through smoke particulates, whereas shorter wavelengths (blues and purples) are filtered out. 

Photo of campanile with orange sky

Photo: UC Berkeley campanile against an orange sky (9/9/20). Photo courtesy of Danny Yim (B.S. '22, ECSE) 

Yes day is night and you can’t see the sun. You woke up and were disoriented. Had to put the lights on in your home at 7 a.m. to see what you were doing. People are wandering around outside wide-eyed and taking photographs on their cellphones.

It might feel like apocalypse, not least on top of a global pandemic that has put us on lockdown for six months, but it’s not.

As Berkeleyside reported yesterday, the ominous orange sky — even darker than it was Tuesday — is caused by smoke from the over 300,000-acre August Complex fires burning in Mendocino and neighboring counties.

The Bay Area is directly downwind from the fires and strong winds are pushing smoke about 5,000 feet up in the air through a process called “turbulent mixing.” Or, as NWS meteorologist Drew Peterson put it: “It’s kind of like if there’s a pile of dust, and someone took a leaf blower to it and flung it all up into the air.”

The sky is orange because longer wavelength light (reds and oranges) are able to push through smoke particulates, whereas shorter wavelengths (blues and purples) are filtered out. And it has gotten progressively darker since (the largely invisible) sunrise.

According to the National Weather Service, as the winds weaken, gravity takes over as the primary vertical transport of the smoke. “Suspended smoke will descend closer to the surface and could lead to darker skies and worsening air quality today,” the agency posted on Twitter, adding, “This is beyond the scope of our models so we rely on your reports!”

Berkeleyans have been sharing dramatic photos on social media since they woke up — describing the view as a “nuclear winter” or  the “Twilight Zone.”

The good news — and boy do we need good news on an eerie day like today — is that the air quality is actually pretty good in Berkeley. According to the Bay Area Air Quality Management District monitor at the Aquatic Park, it was at the yellow, “moderate” level (79 MP2.5) by the 7 a.m. count.

View full story here>

Lightning strikes San Francisco as seen from Berkeley on August 16, 2020

Photo of one of many lightning strikes that started the fire events in the Bay Area. View from Berkeley looking toward San Francisco, Sunday, August 16, 2020. Image: Michelle Nisbet IG: michellenisbetphoto

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