Sacramento skies turn orange, but here’s why the air quality readings aren’t always accurate

In downtown Davis, normally busy with pedestrians and socially distanced coffee drinkers, streets were nearly empty on Wednesday morning as orange, smoky skies and large chunks of ash falling from the sky discouraged residents from venturing outside.

The normally busy Common Grounds coffee shop and the UC Davis arboretum were quiet. Even the typically long, snaking line at Dutch Bros Coffee was only a couple cars in length.

Kristan Evans of Davis, who sat with her coffee outside Mishka’s Cafe, said she has continued to go out despite the smoke, citing it as a frustration.

“I would just be going crazy if I didn’t get out,” Evans said.

The smoke has prompted her to seek relief outside of the valley, traveling to Oakland to visit her daughter and hoping a day trip to Bodega Bay might offer fresh air. Both Oakland and Bodega Bay, however, are also covered in smoke and reported moderate to unhealthy air.

Evans said this year’s smoke and heat have made her consider getting out of Davis, but only in “flashes.” She worries that the length and early arrival of fires marks a new normal for Northern California.

For Evans and others braving the environment on Wednesday, there was some encouragement from AirNow readings showing the Sacramento region ranged from moderate to unhealthy for sensitive groups, with an air quality reading of 83 around noon. That appears to be a significant improvement from Tuesday, when Sacramento was placed in hazardous levels, reaching an astounding AQI reading of 484 at one point from AirNow.

However, a report from the Bay Area suggested air quality readings may be somewhat deceptive.

The National Weather Service in the Bay Area reported that smoke and particles were so dense they were actually causing problems with reporting.

“Suspended smoke will descend closer to the surface and could lead to darker skies and worsening air quality today. This is beyond the scope of our models so we rely on your reports,” the NWS Bay Area wrote on Twitter.

And the agency also warned that Wednesday’s relatively low air quality readings did not reflect the true level of harmful particles in the air, at least in the Bay Area.

The sensors are unable to read matter larger than PM10, which is equivalent to the width of a human hair, the agency said. Large chunks of ash that continue to pollute the air and harm those who inhale them are floating in the atmosphere without being read by the air quality index.

“We just have so much smoke over us right now. Yesterday the models were way off and we expect the same today (for afternoon temperatures),” the NWS Bay Area wrote on Twitter.

The California Air Resources Board explained that while big pieces of ash are harmful, the air quality in Sacramento actually improved Wednesday, as compared to Tuesday, because much of the harmful smoke was trapped high in the atmosphere.

Trapped smoke created orange skies and the smoke remains highly visible. But there was less smoke at the lower levels, where people breathe.

“We’re still breathing smoke, but the air quality is much improved today,” said Melanie Turner of the California Air Resources Board.

The orange skies across Northern California are a result of that trapped wildfire smoke. After strong winds brought ash and smoke from various fires into the region, it has stayed and scattered blue light. Only yellow, orange and red light reaches the surface, creating the apocalyptic-like skies people are seeing.

As the region approaches a month of near-constant unhealthy air, it’s difficult to predict when the smoke will dissipate. Weather can affect how the fire behaves, and wind wind patterns decide where the smoke goes.

Dartanion Mims of the California Air Resources Board said wind is the deciding factor when it comes to smoke.

“The fire you’re looking at isn’t causing your smoke problems. It’s a fire upwind from you that’s doing the real impact,” Mims said.

For some people, the arrival of smoky skies hasn’t really changed daily routines. Evan Ditomaso, a Davis resident, said he obviously isn’t “into” the bad air. But he said he’s mostly been staying indoors anyway in response to the COVID-19 pandemic.

“I’m already not going to go out with friends, so I’m just going to do my own thing at home,” Ditomaso said.

This story was originally published September 9, 2020 at 12:52 PM.