The giant fire that raged for a week at the Lineage cold storage facility in Boyle Heights is finally out, but many Angelenos who lived under clouds of acrid black smoke for days are still worried about air quality.
On Wednesday night, L.A. Material hosted a panel with three air quality experts, who broke down what residents need to know to understand air quality and how to protect themselves.
Our panelists were:
— Yifang Zhu, professor at UCLA's Fielding School of Public Health's Department of Environmental Health Sciences
— Sam Silva, assistant professor of Earth Sciences, Civil and Environmental Engineering, and Population and Public Health Sciences at USC
— Jill Johnston, associate professor in the Department of Environmental and Occupational Health at UC Irvine’s Joe Wen School of Population and Public Health
Watch the full conversation:
Here are five of the top takeaways from our conversation.
1. How should people use the various air monitoring apps and services, especially during a disaster like this?
Most of these air monitoring apps use AQI — the air quality index — to measure the level of pollution in the air. AQI uses a scale from 0 to 500 to indicate the concentration of pollutants (0 to 50 is good, 51 to 100 is moderate). The AQI number you see when you open one of these sites or apps is the average level of pollution from the past 8 to 24 hours. In other words, contrary to what a lot of people assume, it’s not real-time data. Additionally, AQI readings can only tell us how much particulate matter is in the air, not what toxic metals or other substances might be in that particulate matter.
Furthermore, AQI does not detect gases or vapors, which can also be harmful, Professor Yifang Zhu said.
It’s helpful to think of AQI as a baseline for making decisions during an active fire, while also knowing that it doesn’t necessarily convey the full story.
Professor Sam Silva said he relies on his senses of smell and sight in addition to the AQI number.
"Where I live in the San Gabriel Valley, when it's a nice day outside, I can see the mountains," Silva said. "If I go outside and I cannot see the mountains because there is such a bad haze and I'm smelling smoke, it doesn't matter to me what the AQI says. I know that's a pretty gnarly day, and I'm going to be spending most of it inside."
In those circumstances, Silva said, he closes windows and doors and runs two air purifiers — one in his children's bedroom and one in his living room.
If the AQI is in the moderate range and there is no active fire, Silva said he feels good about taking his children outside.
2. What do we know about how quickly air quality recovers after an event like this?
Now that the fire is out, our experts said, outdoor air quality should quickly return to normal.
However, Zhu conducted research studying toxins in the surrounding areas after the 2025 Los Angeles wildfires and "basically found that there [were] lingering effects inside people's homes post-fire for volatile organic compounds. So even when the outdoor air returned to [Los Angeles's] background pollution levels, the indoor levels … continue[d] to be higher than the outdoor [levels] and [those of] the control homes."
This is of greatest concern to people who live close to the storage facility or those who were downwind of the fire.
3. We hear a lot of talk about the impacts on people living “downwind” from the fires. What does “downwind” mean in this context?
Professor Jill Johnston said that "typically in that East L.A. area, the wind will blow to the northeast. So northeast of the facility is Boyle Heights, East L.A., going up [to] maybe City Terrace."
But also, she said: "At night, the winds calm down and can reverse directions." Many residents, Johnston noted, observed that the sight and smell of smoke was particularly fierce in the mornings. That reason for that, she said, was that the winds in the region typically still overnight, so "the pollution sort of sits." Air quality was likely better in the afternoon than in the morning.
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4. What should people in communities closest to the fire be aware of, now that cleanup is beginning?
Johnston said nearby residents should be on the lookout for "dust coming from the facility. If you can see visible dust, then we know there's the potential for the contamination to blow into residential areas."
And finally, she raised the issue of "how they're moving the debris. I know one of the issues from the fires is it brought a lot of truck traffic into some neighborhoods, and if those big trucks weren't covered, then that's another way we can continue to spread some of this contamination."
5. For people who evacuated: When should they come back, and how should they ensure their homes are clean?
Zhu advised caution for those living immediately downwind while cleanup continues, and recommended following protocols similar to those used after wildfires — including industrial hygiene testing and remediation, if needed. "If you can do a test, please do a test … just like you do for the wildfires. Do an industrial hygiene test, see if the reports come back [showing] you need to do any remediation. If you can do remediation, that's always helpful."
Silva said his family evacuated during the Eaton Fire and offered their experience as a point of reference for those in similar situations.
"We made a decision to come back after the smoke had mostly cleared. You could kind of smell it inside, but not extensively — there wasn't ash everywhere," he said. "As we ran an air purifier in the home and ran the HVAC, things cleared up pretty quickly inside our home. … What Yifang is saying is really correct, especially for people who live downwind, but if you live, say, in the general San Gabriel Valley area or something like that, you shouldn't necessarily expect to have to remediate your home after a fire like this."
