As smoke from the Caldor Fire dulls the normally clear skies over Lake Tahoe, UC Berkeley scientists published the first study that examines how well Californians are able to keep the air in their homes safe during wildfire smoke events. (AP photo by Rich Pedroncelli)
Though overall air quality in the U.S. has improved dramatically in recent decades, smoke from catastrophic wildfires is now creating spells of extremely hazardous air pollution in the Western U.S. And, while many people have learned to reduce their exposure by staying inside, keeping windows closed and running air filtration systems on smoky days, data remains limited on how well these efforts are paying off.
In a new study, scientists from the University of California, Berkeley, used data from 1,400 indoor air sensors and even more outdoor air sensors included on the crowdsourced PurpleAir network to find out how well residents of the San Francisco and Los Angeles metropolitan areas were able to protect the air inside their homes on days when the air outside was hazardous.
They found that, by taking steps like closing up their houses and using filtration indoors, people were able to cut the infiltration of PM2.5 particulate matter to their homes by half on wildfire days.
“While the particulate matter indoors was still three times higher on wildfire days than on non-wildfire days, it was much lower than it would be if people hadn't closed up their buildings and added filtration,” said study senior author Allen Goldstein, a professor of environmental engineering and of environmental science, policy and management at UC Berkeley. “This shows that when people have information about the smoke coming their way, they are acting to protect themselves, and they are doing it effectively.”
While individuals can take steps to reduce smoke infiltration to their homes, the ability for air pollution to get inside can also depend heavily on the nature of the building itself. To study these effects, the researchers also used the real estate website Zillow to estimate the characteristics of buildings in the sensor network, including the structure's relative age, the type of building and the socio-economic status of the neighborhood.
Not surprisingly, they found that newly constructed homes and those that were built with central air conditioning were significantly better at keeping wildfire smoke out.
“One of the things that makes this study exciting is it shows what you can learn with crowdsourced data that the government was never collecting before,” said study co-author Joshua Apte, an assistant professor of civil and environmental engineering and of public health at UC Berkeley. “The Environmental Protection Agency (EPA) has a mandate to measure outdoor air quality and not indoor air quality — that's just how our air quality regulations are set up. So, these kinds of crowdsourced data sets allow us to learn about how populations are affected indoors, where they spend most of their time.”
The Air Quality Index across the San Francisco Bay Area measured by crowdsourced PurpleAir sensors on Aug. 28, 2021, when wildfire smoke made air quality unhealthy in much of the region. On the whole, the AQI measured by outdoor sensors (right) was higher than indoor sensors (left), indicating that many residents are taking action to reduce smoke exposure indoors. (UC Berkeley image)
Protecting the air of the great indoors
Like many residents of the Western U.S., both Goldstein and Apte regularly use websites like AirNow and PurpleAir to check how wildfire smoke is affecting the air quality where they live. Both have even installed their own PurpleAir sensors to track the concentrations of PM2.5 particulate matter inside their homes.
So, when UC Berkeley graduate student Yutong Liang wrote a term paper using data from the PurpleAir network to study the impact of wildfire smoke on indoor air quality, Goldstein and Apte thought the work was worth expanding to a full research study.
“Our friends and neighbors and colleagues were all looking at this real-time data from PurpleAir to find out when smoke was affecting their area, and using that information to decide how to behave,” Goldstein said. “We wanted to use actual data from this network to find out how effective that behavior was at protecting them.”
The analysis compared indoor and outdoor sensor data collected during August and September of 2020, when both San Francisco and Los Angeles experienced a number of “fire days,” which the researchers defined as days when the average PM2.5 measured by the EPA exceeded 35ug/m3. This value corresponds to an Air Quality Index (AQI) of approximately 100, which represents the boundary between PM2.5 levels that the EPA considers “moderate” and those that are considered “unhealthy for sensitive groups.”
While scientists are still working to puzzle out just what types of chemical compounds are found in this particulate matter from wildfire smoke, a growing body of research now suggests that it may be even worse for human health than other types of PM2.5 air pollution.
“Wildfires create thousands of different organic chemicals as particulate matter and gases that can cause respiratory and cardiovascular problems in people,” said Liang, who is lead author of the study. “The Goldstein research group is trying to identify these unique compounds, as well as the ways that they react to transform the composition of wildfire smoke over time.”
This simple and inexpensive DIY air filter, constructed from a box fan and a MERV-rated furnace filter, can help reduce the amount of particulate matter in the home. (Photo courtesy Allen Goldstein)
To protect indoor air during fire season, the research team suggests closing up your home before smoke arrives in your area and investing in an air filtration system. If you can't afford a commercial air filter — or they are all sold out — you can also build your own for less than $50 using a box fan, a MERV-rated furnace filter and some tape.
“There are lots of very informative Twitter threads about how to build a good DIY system, and if you are willing to go a little crazy – spend $90 instead of $50 – you can build an even better design,” Apte said. “Every air quality researcher I know has played around with these because they are so satisfying and simple and fun, and they work.”
Where you put the filters also matters. If you only have one, Apte suggests putting it in your bedroom and leaving the door closed while you sleep, to keep the air in your bedroom as clean as possible.
Finally, the researchers suggest cooking as little as possible during smoky days. Cooking can generate surprising amounts of both particulate matter and gases, neither of which can be easily ventilated out of the house without inviting wildfire smoke in.
“Air filters can help remove particulate matter from cooking, but running a kitchen or bathroom exhaust fan during smoke events can actually pull PM2.5 -laden air from outdoors to indoors,” Goldstein said.
In the future, the researchers hope to find ways to sample the indoor air quality of a more diverse array of households. Because PurpleAir sensors cost at least $200 apiece, households that contribute data to the network tend to be affluent, and the Zillow estimates show that the average price of homes in the network is about 20% higher than median property values in their areas.
“One thing that we're deeply interested in is understanding what happens to people in indoor environments, because that's where people spend most of their time, and there's still an awful lot we don't know about indoor pollution exposure,” Apte said. “I think that these new methods of sensing the indoor environment are going to allow us to grapple a lot more with questions of environmental justice and find out more about who gets to breathe cleaner air indoors.”
Co-authors of the paper include Deep Sengupta, Mark J. Campmier and David M. Lunderberg of UC Berkeley.
This work was supported by the National Oceanic and Atmospheric Administration Climate Program Office's AC4 program (Award NA16OAR4310107) and the California Air Resources Board (Award 19RD008). This publication was also developed as part of the Center for Air, Climate and Energy Solutions, which was supported under the Assistance Agreement R835873 awarded by the U.S. EPA. It has not been formally reviewed by the EPA.
Drone sensors for deployment into a local ignition event Courtesy of Kevin Schwarm
As California and other states continue to battle extreme heat this fire season,KevinSchwarm, who is pursuing a Ph.D. attheUCLASamueli School of Engineering, has been fighting fire with fire alongside other researchersatBlodgett Forest in Northern California.
Using new drone sensing technology, Schwarm has helped contribute to a new way of measuring the emissions of fires — carbon monoxide, carbon dioxide, particulates, volatile organic compounds, etc. — so researchers can gain a deeper understanding of the way wildfires behave.
When controlled properly, the so-called prescribed burns — fires that are intentionally set to clear out vegetation that otherwise could end up fueling larger, more catastrophic fires — can play a key role in maintaining the health of a forest. They help prevent the kinds of wildfires that have wiped out homes and caused devastating losses of lives across California in recent years.
While setting fire to the forest mayseemcounterintuitive to the goal of preventing wildfires, it draws inspiration from Native American practices of setting controlled fires to improve the habitats for deer and other game animals.
Since the Gold Rush, however, the amount of plant life in forests in California has proliferated. While this growth is ostensibly good for the health of the forests, the extra vegetation actually increases the risk of extreme wildfires as it provides large amounts of fuel.
Located about 142 miles east of UC Berkeley on the western slope of the central Sierra Nevada, the 4,400-acre Blodgett Forest Research Station has been a living laboratory since 1933. In April, Rob York, an assistant Cooperative Extension specialist and adjunct associate professor of forestry at UC Berkeley, directed a field campaign involving four days of controlled burns. Scientists and forestry experts from other universities, including UCLA and UC Riverside, joined in the effort to reduce wildfire risk.
Working with engineers from OptoKnowledge, Schwarm was a part of several research teams in charge of measuring the emissions of the prescribed burns. They monitored the emissions using a drone that features on-board, optical sensors that can measure levels of airborne carbon monoxide and carbon dioxide. The team also used the data to create aerial maps that correlate the emissions with the fires, as well as other ground and air measurements.
Schwarm, whose doctoral research focuses on optical diagnostics for combustion systems and harsh environments, was responsible for monitoring the data collection, working with the optical sensor equipment and guiding the drone pilots during the tests.
“The objective was to capture as much information as possible on the emissions of these fires and also to relate those to the burned vegetation that was inventoried beforehand,”saidSchwarm, who works in the lab ofMitchellSpearrin, a professor of mechanical and aerospace engineeringatUCLASamueli. “We are hoping that the results of this field campaign will help to further our understanding of wildfire combustion science, the role of wildfires in our local and global climate, and to help us develop more efficient wildfire management strategies.”
A Maine native who loves the outdoors, Schwarm was initially interested in research involving internal combustion engines when he first visited UCLA in 2017 as a prospective graduate student. After meeting Spearrin and learning about his research on laser diagnostics and combustion systems, Schwarm was intrigued and decided to join Spearrin's research group that fall.
“I found Professor Spearrin's research very compelling, with laser diagnostics providing an avenue for engine research while also remaining an elegantly simple yet powerful measurement tool with wide applicability,” Schwarm shared.
Last fall, Spearrin introduced Schwarm to the multicampus wildfire project. “I found it a very exciting opportunity to use our expertise in combustion diagnostics to play a role in enhancing our understanding of both wildfires and climate change, which could lead to better methods for managing these grave issues,” Schwarm said.
According to Schwarm, the preliminary results from emissions data collected during the field campaign indicate that the drone sensor was very effective in capturing the multi-dimensional gradients of emissions in the fire plumes.
The team has been able to create three-dimensional spatial maps of the emissions concentrations, tracking how they change over time. This finding provides the researchers with insight into how fires behave, such as where the boundaries of the fire are and where new ignition sites emerge.
“This is very exciting as a new sensor capability to provide a deeper level of information for a wide range of applications in wildfire science and management, and we are currently working with the other researchers involved in the burns to place that information into context,” Schwarm said. “This was the first full-scale, real-world test for our drone sensor, and it will serve as a strong foundation for future deployment and expansion of our methods.”
A summer of smoke and ash in many parts of California has raised questions about the safety of produce growing on farms and in the garden, eggs laid by chickens who peck around in ash-laden areas, and remediation needed to safely and effectively grow food in the future.
UC Agriculture and Natural Resources brought together experts who have researched the effects of previous fires' fallout and studied soil contaminants to share their insight in a two-hour webinar now available on YouTube.
“The No. 1 health concern during a fire is smoke inhalation, and it's been well documented that wildfire smoke can negatively impact both the heart and the lungs,” said Claire O'Brien, a pharmacology and toxicology doctoral student at UC Davis. “However, the chemicals found in the smoke don't just stay in the air. They can deposit onto plants and into soil and water.”
Although every fire is unique, some generalizations can be drawn from research conducted following previous fires. UC Cooperative Extension food systems advisor Julia Van Soelen Kim detailed a study conducted following the October 2017 wildfires in Sonoma County and across the North Bay.
With the help of UC Master Gardener and community volunteers, the researchers collected over 200 samples of homegrown collard greens, lettuces, kale and chard that were exposed to wildfire smoke and ash. A subset of the samples were analyzed by a private laboratory.
“There was very low concern about chemicals on produce,” Van Soelen Kim said. “No samples had detectable levels of lead, arsenic, mercury or chromium. And that's a huge sigh of relief.” However, analytical results vary by site, site history and by fire event, and few have pre-fire baseline data to compare with.
Van Soelen Kim said basic food-safety practices should be followed when preparing to eat food grown in a home garden, regardless of ash or smoke contamination.
“You should always wash your hands before and after harvesting, and wash your produce in running water to mitigate any kind of potential risk,” she said.
Another study outlined at the webinar used a similar process to determine whether there might be contaminants in the eggs laid by backyard poultry that live and feed in areas exposed to wildfire ash and smoke.
Scientists know from previous research that chickens exposed to lead in their environment can produce eggs with high lead content and that heavy metal content of ash from urban wildfires is higher than from rural wildfire.
“We combined those two pieces of research with what we know that chickens do all day: they peck at the ground for hours on end,” said Todd Kelman, a veterinarian in the School of Veterinary Medicine at UC Davis. “That makes for a pretty good hypothesis that urban wildfire could pose a risk for the production of eggs and poultry that contain heavy metals.”
Kelman and his team put out a call for eggs from backyard poultry and received samples from 344 premises in fire-affected and non-fire-affected areas of California.
Surprisingly, egg samples that contained higher lead levels came from parts of the state that were not directly impacted by ash and smoke.
“Did our data support our hypothesis that proximity to urban wildfire is a driving source for lead in eggs of backyard poultry? The answer is not so much,” Kelman said. “So, is it safe to eat eggs from your backyard poultry? We can't give you a definitive answer to that question. But we do suggest you assess your risk and reduce the risk of contamination.”
Practices that reduce the risk include keeping chickens off the ground, using a chicken feeder that prevents spillage onto the ground and making calcium readily available, for example in the form of oyster shells, because calcium can prevent the absorption of lead. Making sure that chickens are provided uncontaminated water is also an important part of risk reduction.
For confirmation on the safety backyard chickens and their eggs, lab tests for eggs are available for $60 from the California Animal Health and Food Safety Laboratory at UC Davis, or chickens may be submitted to CAHFS for necropsy.
Fire effects on soil is another consideration in burned areas, said UC Cooperative Extension urban agriculture advisor Rob Bennaton.
“Fires heat topsoil layers. They reduce the amount of living micro-organisms at the site of the burn, and also affect organic matter and nutrients. Ash deposits over time may make soils more alkaline,” he said. “As a result of these combined factors, there are temporary changes in nutrient levels and the capacity for soils to exchange nutrients for optimal plant growth and nutrition.”
With proper land care and management, soils can be remediated over time.
“It won't happen overnight. Soils were developed over millions of years,” he said.
Some ways to improve safety when gardening in fire-affected areas including keeping the soil covered with wood chips or other landscape mulch to reduce airborne soil dust. Use drip irrigation to prevent up splash onto the undersides of growing vegetables. Promote good drainage, especially at the bottom of slopes to prevent the concentration of contaminants.
Lab tests are often needed to determine the soils' post-fire characteristics. “Don't guess, but test,” Bennaton said.
The UC Master Gardener Program can provide technical assistance to help home gardeners find resources for home soil testing, he said.
Additional resources and information shared during the webinar include:
Post-fire soil resources and soil testing information
Research on produce safety and backyard chicken egg safety after the 2017 wildfires in California is available on this web page. To view a past webinar recording with these research findings, click this link.
A summer of smoke and ash in many parts of California has raised questions about the safety of produce growing on farms and in the garden, eggs laid by chickens who peck around in ash-laden areas, and remediation needed to safely and effectively grow food in the future.
UC Agriculture and Natural Resources brought together experts who have researched the effects of previous fires' fallout and studied soil contaminants to share their insight in a two-hour webinar now available on YouTube.
“The No. 1 health concern during a fire is smoke inhalation, and it's been well documented that wildfire smoke can negatively impact both the heart and the lungs,” said Claire O'Brien, a pharmacology and toxicology doctoral student at UC Davis. “However, the chemicals found in the smoke don't just stay in the air. They can deposit onto plants and into soil and water.”
Always wash your hands before and after harvesting, and wash your produce in running water to mitigate a potential risk. (Photo: Evett Kilmartin)
Although every fire is unique, some generalizations can be drawn from research conducted following previous fires. UC Cooperative Extension food systems advisor Julia Van Soelen Kim detailed a study conducted following the October 2017 wildfires in Sonoma County and across the North Bay.
With the help of UC Master Gardener and community volunteers, the researchers collected over 200 samples of homegrown collard greens, lettuces, kale and chard that were exposed to wildfire smoke and ash. A subset of the samples were analyzed by a private laboratory.
“There was very low concern about chemicals on produce,” Van Soelen Kim said. “No samples had detectable levels of lead, arsenic, mercury or chromium. And that's a huge sigh of relief.” However, analytical results vary by site, site history and by fire event, and few have pre-fire baseline data to compare with.
Van Soelen Kim said basic food-safety practices should be followed when preparing to eat food grown in a home garden, regardless of ash or smoke contamination.
“You should always wash your hands before and after harvesting, and wash your produce in running water to mitigate any kind of potential risk,” she said.
Keeping chicken feed off the ground and providing clean water are two ways to reduce the risk of contaminated eggs. (Photo: USDA)
Are backyard chicken eggs safe to eat?
Another study outlined at the webinar used a similar process to determine whether there might be contaminants in the eggs laid by backyard poultry that live and feed in areas exposed to wildfire ash and smoke.
Scientists know from previous research that chickens exposed to lead in their environment can produce eggs with high lead content and that heavy metal content of ash from urban wildfires is higher than from rural wildfire.
“We combined those two pieces of research with what we know that chickens do all day: they peck at the ground for hours on end,” said Todd Kelman, a veterinarian in the School of Veterinary Medicine at UC Davis. “That makes for a pretty good hypothesis that urban wildfire could pose a risk for the production of eggs and poultry that contain heavy metals.”
Kelman and his team put out a call for eggs from backyard poultry and received samples from 344 premises in fire-affected and non-fire-affected areas of California.
Surprisingly, egg samples that contained higher lead levels came from parts of the state that were not directly impacted by ash and smoke.
“Did our data support our hypothesis that proximity to urban wildfire is a driving source for lead in eggs of backyard poultry? The answer is not so much,” Kelman said. “So, is it safe to eat eggs from your backyard poultry? We can't give you a definitive answer to that question. But we do suggest you assess your risk and reduce the risk of contamination.”
Practices that reduce the risk include keeping chickens off the ground, using a chicken feeder that prevents spillage onto the ground and making calcium readily available, for example in the form of oyster shells, because calcium can prevent the absorption of lead. Making sure that chickens are provided uncontaminated water is also an important part of risk reduction.
For confirmation on the safety backyard chickens and their eggs, lab tests for eggs are available for $60 from the California Animal Health and Food Safety Laboratory at UC Davis, or chickens may be submitted to CAHFS for necropsy.
The UC Master Gardener Program can provide technical assistance to help home gardeners find resources for home soil testing. (Photo: USDA)
Are soils safe for growing food after a fire?
Fire effects on soil is another consideration in burned areas, said UC Cooperative Extension urban agriculture advisor Rob Bennaton.
“Fires heat topsoil layers. They reduce the amount of living micro-organisms at the site of the burn, and also affect organic matter and nutrients. Ash deposits over time may make soils more alkaline,” he said. “As a result of these combined factors, there are temporary changes in nutrient levels and the capacity for soils to exchange nutrients for optimal plant growth and nutrition.”
With proper land care and management, soils can be remediated over time.
“It won't happen overnight. Soils were developed over millions of years,” he said.
Some ways to improve safety when gardening in fire-affected areas including keeping the soil covered with wood chips or other landscape mulch to reduce airborne soil dust. Use drip irrigation to prevent up splash onto the undersides of growing vegetables. Promote good drainage, especially at the bottom of slopes to prevent the concentration of contaminants.
Lab tests are often needed to determine the soils' post-fire characteristics. “Don't guess, but test,” Bennaton said.
The UC Master Gardener Program can provide technical assistance to help home gardeners find resources for home soil testing, he said.
Additional resources and information shared during the webinar include:
Post-fire soil resources and soil testing information
Research on produce safety and backyard chicken egg safety after the 2017 wildfires in California is available on this web page. To view a past webinar recording with these research findings, click this link.