When Will the Air Quality Improve in California?

But what has continued to astonish experts is the unprecedented scale of the fires this year.

[Read about the deaths, which have devastated communities up and down the coast.]

On Friday, Gov. Gavin Newsom gave his usual virtual news briefing standing among trees charred by the raging North Complex Fire, in the midst of a yellowish haze.

He sounded a dire warning about the realities of climate change and railed against federal leaders who he said were falsely denying its realities.

“California is America in fast forward,” he said. “What we’re experiencing right now is coming to communities all across the country.”

While the governor acknowledged that poor forest management over decades has contributed to the severity of wildfires in recent years, he said that mega-droughts and record-breaking heat waves were undeniable evidence that many of the extreme predictions about climate change had already come true.

[Read about how the fires, raging where they don’t usually burn, represent a new climate menace for Oregon.]

“My 4-year-old has moved from talking about a novel coronavirus — his actual words — to asking me why he can’t play around outside with a soccer ball,” he said. “That’s not the world that I want to leave to our kids.”

Millions of Californians were effectively homebound by toxic air over the weekend in a grim preview of the months that could be ahead. It’s still only September, after all.

In my Los Angeles neighborhood, I could smell and feel the smoke in my throat during a short walk down the block on Saturday. A sooty film had settled on the trees and cars, and the sun was visible as a glowing red circle in a gray-brown sky.

A look at PurpleAir’s map was a depressing exercise; few of the outdoor monitors in California registered less than 100 on the Air Quality Index.

Late last week, I asked Edward Smith, a forest ecologist with the Nature Conservancy, how long the fires might burn.

“In many cases, the fires will burn until they run out of fuel or the winter rains come,” he said in an email. Running out of fuel can mean running into physical barriers like granite or bodies of water, or irrigated pastures.

[Track the biggest fires burning on the West Coast and see the air quality in your area.]

Although meteorologists said the weather was expected to help in coming days, Mr. Smith said, “it could still be several weeks, especially when suppression forces within states and across the West are drawn down to such low levels.”

Dr. Mary Prunicki, the director of air pollution and health research at Stanford University’s Parker Center for Allergy and Asthma Research, told me that so many variables affect air quality that it’s practically impossible to predict when and where the air will be safe.

“In the past, it hasn’t looked so dire so quickly,” she said. “It’s pretty scary — and it combines with the Covid-19 pandemic. It’s a layering effect.”

Research has clearly shown that the health impacts from wildfire smoke can be seen immediately in things like cardiac and respiratory distress calls.

[Here’s how to protect yourself from wildfire smoke exposure.]

And prolonged exposure is bad. That’s one reason fires disproportionately hurt already vulnerable populations; lower-income people are more likely to live in places where air quality is bad all the time, like the Central Valley, which has long had some of the nation’s worst air.

But on the flip side, Dr. Prunicki said, air quality can improve quickly and the dangers can ease quickly, too — “even in an afternoon.”

So in order to determine whether it’s safe to go outside, she recommended checking the Air Quality Index before you leave.

And even if air quality is not listed as dangerous, Dr. Prunicki emphasized that you may still feel negative effects.

“There are arguments that cutoffs should be tighter and more specific for different groups, but it’s pretty vague,” she said. “It’s important to listen to your body.”

(This article is part of the California Today newsletter. Sign up to get it by email.)

Read more about the fires:

  • President Trump is scheduled to visit California today as fires pummel the nation’s most populous state and the entire West Coast. [The New York Times]

  • In visiting the state, he’ll be confronting a reality he denies. [The New York Times]

  • Firefighters are bracing for stronger winds, which could both clear the air and fan the flames. [The New York Times]

  • “They’re still able to be in school, even though the school burned to the ground.” Fires are disrupting schools — so the fact that educators were already preparing for remote school is actually helpful. [The New York Times]

  • Football was back on Sunday. In Los Angeles, that meant the Rams squared off against the Dallas Cowboys and the 49ers played the Arizona Cardinals in spite of concerns about air quality. [CBS Sports]

  • Here’s what to know before buying an air purifier for your home. [The New York Times]

  • In Los Angeles, agents made 300 arrests. More than a thousand others were rounded up in New York, Atlanta, Phoenix and other cities. After a pandemic pause, Immigration and Customs Enforcement has resumed large-scale deportation arrests. [The New York Times]

  • Two Los Angeles County Sheriff’s deputies were shot and critically injured in what department officials described as an ambush in Compton. They are expected to recover. [The New York Times]

  • Killings by Vallejo police officers have drawn attention and outrage. But at least 60 people since 2014 have said they were the victims of heavy-handed tactics, even if the encounters with officers didn’t end in their deaths. [The San Francisco Chronicle]

  • Senator Kamala Harris’s parents met in Berkeley and found a home in the Black study group whose ideas gave rise to the Black Power movement. [The New York Times]

  • “Keeping Up With the Kardashians” is ending. Here’s a look back at some of the ways it has changed the world. [The New York Times]

California Today goes live at 6:30 a.m. Pacific time weekdays. Tell us what you want to see: CAtoday@nytimes.com. Were you forwarded this email? Sign up for California Today here and read every edition online here.

Jill Cowan grew up in Orange County, went to school at U.C. Berkeley and has reported all over the state, including the Bay Area, Bakersfield and Los Angeles — but she always wants to see more. Follow along here or on Twitter, @jillcowan.

California Today is edited by Julie Bloom, who grew up in Los Angeles and graduated from U.C. Berkeley.