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TL;DR: The LA wildfires caused major damage and released harmful pollutants. Although air quality has improved significantly since these fires began, and regular activities can be resumed, ash should be cleaned up by professionals and precautions may need to be taken near burn areas. Some larger particles and gaseous air toxics can linger for months, and we need more research on wildland-urban interface fires.
The recent LA fires were profoundly devastating. On the morning of January 7th, an initial fire erupted in the Pacific Palisades, destroying or damaging more than 6,800 structures. Shortly after, the Eaton fire sparked to life, destroying or damaging 10,491 structures. Even more fires blazed into being, including the Hughes fire, which tragically killed at least 29 people collectively.
These fires produced many harmful air pollutants while they were burning, but a significant amount of time has passed since then. In the last few weeks, people have been allowed to return to their homes in burn or near-burn areas. So, now, over a month since the fires began, what is the state of LA’s air quality? What, if any, air pollutants remain from the fires?
Wildland-urban interface (WUI) fires, such as those that recently burned in LA, differ from other kinds of wildfires because they burn not only vegetation but also man-made structures and urban environments. These burns produce a complex mixture of different compounds and gases. A full list of the possible chemical pollutants can be found here. However, the South Coast Air Quality Management District has identified the following groups of pollutants of concern:
- Particulate matter
- Gaseous air toxics
Particulate Matter
Particulate matter refers to any solid or liquid compounds that are in the air. All wildfires produce particulate matter. However, WUI fires may produce especially concerning particulate matter from the burning of houses and structures.
Particulate matter air pollution is typically categorized into two groups:
- PM2.5
- PM10
PM2.5: Measured by most low-cost air quality sensors
PM 2.5 refers to any particulate matter with a diameter of 2.5 micrometers or smaller. Due to their small size, these particles can penetrate deep into the lungs and even into the bloodstream. WUI fires can produce many concerning PM2.5 particles, such as metals like lead and arsenic, which can spread very far from their source.
Fortunately, although these particulates are harmful to human health, air dilution — time spent mixing with the atmosphere — makes these air pollutants short-lived. Professor of atmospheric and oceanic sciences at UCLA, Suzanne Paulson, explains that the levels of airborne metals in LA, for instance, have essentially returned to normal.
Clarity Movement provides air quality sensors that measure PM2.5. Although these measurements do not specify which particulates they are detecting, Clarity’s Nodes are a good way to determine the overall levels of particulates in the air. Our public air quality data-sharing platform was especially helpful in determining current air quality safety when the wildfires were actively burning in Los Angeles since the Los Angeles Unified School District has a network of 200+ Node-S devices across their district.
PM10
Unfortunately, there is another kind of particulate matter that is not picked up by most low-cost air quality sensors. This is PM10, which consists of particulate matter with a diameter of 10 micrometers or smaller. Clarity will soon be releasing a new air quality measurement device that produces highly accurate PM10 readings (join our upcoming Showcase webinar to learn more). These particulates tend to be slightly heavier than PM2.5 and, thus, do not disperse into the atmosphere as easily. Instead, they fall to the ground and can remain in the same areas for longer periods of time.
WUI fires produce ash, which is a type of PM10. Ash can contain many toxic materials, such as asbestos from the burning of old homes. Ash can often be seen with the naked eye. When an ash plume can be seen in your vicinity, it is a good idea to stay inside or use precautions to protect against this form of air pollution.
Since ash plumes from the LA fires have long since dissipated, the danger mainly exists when the ash that has fallen to the ground is disturbed and kicked up into the air. This is why clean-up of the burn areas must be done by professionals. Luckily, these efforts are already taking place and will include the removal of ash in ways that minimize resuspension.
If you need to clean up ash on your own property, it is important to take proper precautions in order to remain safe.
Gaseous air toxics
A wide variety of toxic gases are produced by WUI fires. Many are not picked up by most low-cost air quality sensors, requiring highly specialized, expensive air quality measurement equipment to detect. However, these gases contribute to the smell of a fire, so they can be detected to some degree by your nose — which is an “air pollution monitor” with thousands of years of R&D! This is why it is a good idea to take precautions if you smell smoke or other unusual odors, even if the local air quality index (AQI) is in the healthy range.
That being said, Professor Suzanne Paulson of UCLA has also specified that both PM2.5 and gaseous air toxic concentrations are controlled by air dilution. In other words, wind and air mixing cause both PM2.5 and gaseous air toxics to dissipate into the atmosphere. In fact, some of these compounds, like certain polycyclic aromatic hydrocarbons (PAHs), even attach to PM2.5 particles. This means that when PM2.5 is low, the levels of gaseous air toxics will likely be low as well, and AQI is still a fairly good indicator of gaseous air quality.
WUI fires can release a plethora of toxic gases into the air. Some of these compounds are volatile organic compounds (VOCs), which are organic compounds with vapor pressures high enough to exist in the atmosphere primarily in the gas phase.
Benzene, for instance, is one of the many VOCs released by WUI fires. It can be found in gasoline and causes drowsiness, dizziness, and unconsciousness, as well as various kinds of redness and irritation. It is also a carcinogen, with a host of negative effects from chronic exposure.
Fortunately, mobile outdoor air quality monitoring results from the recent Eaton and Palisades wildfires showed that there are currently no elevated levels of benzene or other measured VOCs in the burn areas. A study measuring the levels of benzene and other hazardous gases after the Marshall fire similarly found reduced (although not entirely absent) levels of benzene in burn areas.
Even with these reassuring measurements, it is important to note that some gaseous air toxics can still linger long after the fires are over. Professor Paulson warns that PAHs have the potential to remain in burn areas for extended periods of time. Moreover, VOCs can deposit on indoor walls and surfaces where they may keep off-gassing, producing a smoky smell, for months.
If the latter is the case in your home, off-gassing of VOCs is temperature-dependent, so they will become more potent with heat, but should still naturally reduce over time. Even so, there are steps you can take to clean the air inside your house and mitigate any adverse health effects.
Looking to the Future
Air quality has improved significantly, and Los Angeles is beginning to move forward and rebuild after the horrific January fires. Professor Paulson and the South Coast Air Quality Management District both explain that if the AQI is good, there is no visible ash, and smoke cannot be smelled, then there is no reason to curtail your regular activities.
Yet, more research is needed to fully understand the effects of WUI fires and their aftermath. Especially with the onset of climate change, these kinds of wildfires will only become more frequent. Increased research into WUI fires and their health effects would allow us to better prepare and protect populations at risk. Outdoor air quality monitors such as those made by Clarity can help with this kind of research — feel free to contact us if we can help with your wildfire-related air quality measurement needs.