Thought Leaders

Exploring Challenges in Wildland Urban Interface Fire Chemistry

Thought LeadersDr. Amara HolderMechanical EngineerUS Environmental Protection Agency's Office of Research and Development

In this interview conducted at Pittcon 2024 in San Diego, we spoke to Amara Holder from the US Environmental Protection Agency about the chemistry of fires in the wildland-urban interface.

Could you briefly introduce yourself and describe what inspired you to focus on the study of emissions from combustion systems, particularly those from wildland fires?

My name is Amara Holder, and I work as a mechanical engineer at the US Office of Research and Development at the EPA. My journey into this field began during my time in graduate school, where I delved into the intricate world of combustion emissions. Specifically, I was captivated by the chemistry behind emissions from diesel generators and their implications on toxicology.

At the EPA, my focus has expanded, encompassing a broader spectrum while retaining a sharp focus. I’m deeply engrossed in investigating the chemical and physical attributes of any emission source that contributes to atmospheric pollution, ultimately impacting air quality.

One particular area of interest for me is wildfires, given their status as one of the most significant contributors to atmospheric emissions. Their repercussions are far-reaching, affecting millions of people and leading to a myriad of health issues, including fatalities. So, we need to gain a better understanding of what chemicals are present in smoke.

In your role at the EPA’s Office of Research and Development, what have been some of the key findings that you’ve noticed from your study of toxic emissions from wildland fires?

Our research has unveiled crucial insights into wildfire emissions. One significant discovery is that fires release trace levels of various types of toxics. While these emissions may not rank as the most prominent output from a fire, such as particulate matter, the sheer scale and frequency of wildfires make them substantial contributors of these toxics to the atmosphere.

Even though the emission levels of these toxics may be low individually, they can collectively have a significant impact due to the extensive nature of wildfires. Therefore, accurately characterizing these trace-level emissions from wildfires is imperative when compiling emissions inventories for individual toxic compounds.

Additionally, we have determined that the type of fuel burned and the conditions of combustion play pivotal roles. Fires that creep up on the wildland-urban interface, consuming structures and vehicles, produce emissions distinct from those occurring in natural landscapes. This distinction is critical in understanding the emissions of toxics, highlighting the importance of considering fuel type and combustion conditions in assessing wildfire impacts.

Drawing comparisons between emissions from wildfires and their impact on health with those from industrial sources can be quite challenging. We continue to grapple with understanding the intricate relationship between emission chemistry and its health effects. However, what we do know is that wildfires discharge vast quantities of particulate matter into the atmosphere.

Particulate matter, regardless of its specific chemical composition, serves as a major catalyst for adverse health effects. Compared to most industrial sources, wildfires emit substantially larger amounts of particulate matter. This discrepancy arises from the considerable success achieved by the EPA in regulating emissions from industrial sources in addition to the large increases in the magnitude of wildfires that have occurred over the past two decades. Consequently, the substantial emissions from wildfires significantly contribute to adverse health effects due to the sheer volume of pollutants released into the atmosphere.

Image Credit: CI Photos/

How has your research contributed to understanding and managing air quality impacts near wildfires?

My research primarily involves generating data for EPA systems. I delve into emissions and emission factors, which are integral in crafting emissions inventories. These inventories play a pivotal role in pinpointing sources that necessitate regulation and devising effective strategies for reducing pollutants in the atmosphere.

I also work on different aspects of wildfire smoke, including the volatility distribution. This helps us understand how emissions evolve over time and travel downwind after entering the atmosphere. By unraveling these dynamics, we can gain valuable insights into the downstream impacts on air quality stemming from wildfires.

It is important to point out that the agency has only recently focused on wildfires as they became a more prominent pollution source. 

Could you share more about the advancements in the methods and technologies used to inventory wildfire smoke toxics and monitor the air quality impacts near fires? Have you noticed a large evolution of these technologies over time?

We have been studying wildfire emissions for over 40 years. One of the most exciting parts of this journey has been the advancements in our analytical tools. Back in the day, we had emission factors dating back decades, but a lot of it was like looking for a needle in a haystack—many non-detects. Now, with our super-sensitive measurements, we can actually quantify those tiny levels. It is a game-changer, especially when it comes to tracking toxic emissions.

We now also have many more online capabilities for measuring emissions in real time, which allows us to examine how the emissions evolve during the fire. This real-time data is gold. It helps us understand not just what is coming out of the fire but how it changes over time and what factors influence its spread in the air.

The other significant advancement is in ambient monitoring networks. Currently, we have a regulatory monitoring network that’s primarily focused on examining day-to-day concentrations of pollutants emitted from urban industrial sources. These sources typically exhibit consistent emissions over time; for instance, a power plant consistently emits pollutants, and vehicle emissions are continually dispersed throughout an area. Therefore, a single central monitor is often used to represent an entire area.

Wildfire smoke, on the other hand, is very different as it involves relatively small fire fronts emitting high concentrations of pollutants into a plume. This plume then disperses into the atmosphere, potentially spanning across mountain ranges and valleys. Consequently, we observe a significant concentration gradient from the vicinity of the fire to distant areas, with concentrations changing rapidly over time.

For instance, fire activity may not be as intense in the morning as it is in the afternoon. Consequently, we observe fluctuations in concentrations throughout the day. Moreover, depending on shifts in wind direction, the impact area may change. However, the existing ambient monitoring network is not equipped to capture these dynamic variations.

Recognizing the significant impact of wildfires on air quality, many states have incorporated additional monitors to understand these fluctuations better. Nevertheless, the major breakthrough has been the emergence of low-cost sensors. Now, individuals can install devices like PurpleAir or other sensors in their backyard, and the data collected is shared on cloud platforms for public access.

To this end, the EPA has collaborated with the US Forest Service to develop the AirNow Fire and Smoke Map. This platform utilizes data from the multitude of low-cost sensors reporting and converts it into accurate measurements that can be compared with regulatory standards. The map effectively illustrates the spatial gradients of wildfire smoke and provides high-resolution updates every 10 minutes, offering valuable insights into the dynamic nature of air quality impacted by wildfires.

What are some of the low-cost approaches that you have researched for reducing smoke exposure, and how effective have they been in practical scenarios?

We have been exploring strategies to mitigate exposure to smoke, recognizing that we cannot regulate ourselves out of wildfires. Thus, having tools to reduce smoke exposure becomes paramount. During wildfire smoke events, air cleaners, which are highly effective at reducing smoke concentrations, quickly sell out and can often be prohibitively expensive for some. As an alternative, many turn to what is known as a do-it-yourself air cleaner, typically consisting of a box fan with a furnace filter attached.

These makeshift air cleaners have proven to be quite effective at reducing smoke concentrations. Interestingly, increasing the number of filters on these box fans enhances their effectiveness. Designs featuring four or even five filters arranged in a box shape, known as Corsi-Rosenthal boxes, can be as effective as commercial air cleaners costing hundreds of dollars.

What makes them particularly appealing is their accessibility. All that is needed is a standard box fan, readily available at hardware stores, and furnace filters, making them a more feasible option for many compared to other types of air cleaners.

Pittcon Thought Leader: Amara Holder

This initiative has largely been community-driven, with numerous instructional videos available online. Its popularity surged during the pandemic as people sought ways to reduce the risk of contracting COVID-19, but it is particularly relevant in areas heavily affected by wildfire smoke. Local air quality agencies in these regions often actively engage in educating and assisting individuals in constructing these air cleaners, sometimes even providing the necessary materials.

In your presentation, you mention challenges in measuring certain chemical compounds emitted from WUI fires. Can you elaborate on these challenges and any potential solutions you foresee?

One of the primary challenges posed by these fires is their complete unpredictability and the speed at which they occur. It is hard to anticipate when and where they will occur, and when they do happen, it usually happens in a matter of hours. By the time the fire ignites and advances toward a community, it can swiftly engulf and destroy it before you even have a chance to mobilize. Thus, it can be really difficult to get a measurement when the opportunity is gone before you have even had a chance.

Another issue is that some of the measurements we want to take of toxic compounds require instruments that are substantially more difficult to set up and might be challenging to mobilize quickly. So, it is really difficult to get the measurements we want in the place we want.

One approach to address this is through aircraft-based research, a common method used for studying wildfire smoke. This involves equipping aircraft with advanced instrumentation and conducting campaigns to fly to targeted areas. But the risk with that is that you could sit for months or longer, waiting for a wildland-urban interface fire to occur, or it might not ever happen.

Alternatively, ambient monitoring networks present another avenue. Historical data from monitors affected by wildfire smoke can offer insights. Yet, this approach faces its own set of challenges. The monitors measuring the specific compounds of interest often operate on irregular schedules, such as one in three or one in six days, which limits the frequency of measurements.

Capturing smoke plumes at ambient monitoring sites relies heavily on luck—both in terms of the plume hitting the site and the site operating on the desired day. To enhance our chances of capturing relevant data, increasing the frequency of sampling at monitoring networks situated in fire-prone areas during peak fire seasons could prove beneficial.

Another avenue involves laboratory simulations. Various studies are adopting this approach, using urban materials in controlled environments to recreate fire conditions and emissions. However, this method also has limitations, as replicating the exact conditions of wildland-urban interface fires, particularly wind-driven dynamics with speeds reaching 50 to 60 miles per hour, proves challenging.

These very extreme conditions, with temperatures high enough to melt metal, are hard to replicate in a laboratory setting. Additionally, combustion systems can be difficult to scale. Burning an entire vehicle presents significant challenges in experimental settings. Scaling down such a complex process into a manageable experiment is equally as challenging.

Conducting these types of experiments also requires substantial resources, and even with ample funding, only a limited number of experiments can be conducted. Consequently, the data generated from such experiments is often sparse, further complicating efforts to understand and address the complexities of these fires fully.

How do the emissions from wildland-urban interface fires differ chemically from those from other wildfires? And what implications does this have for environmental and public health?

Our findings have suggested that fires involving urban materials tend to emit compounds with notably different chemistry. We expect to see a heightened presence of metals in these instances. We also expect to see elevated levels of chlorinated hydrocarbons due to the greater abundance of chlorine in urban settings compared to natural environments.

Similarly, we anticipate increased concentrations of nitrogen compounds, such as cyanates, attributed to the higher nitrogen content in urban areas as opposed to natural landscapes. These disparities in the chemical composition of the fuel are believed to impact the emissions generated by such fires.

Our understanding suggests that emissions can become more toxic when chlorine, nitrogen, and similar elements are present in the initial fuel mix. While conclusive evidence regarding the heightened toxicity of these emissions is lacking, we have a strong suspicion that they are.

Similarly, urban fire settings, where firefighters encounter structure fires, can pose significant health risks. Without proper protective equipment and adherence to cleaning protocols, these firefighters are susceptible to health effects. When considering wildland-urban interface fires, these risks are amplified on a larger scale. Such incidents not only jeopardize the health of first responders but also pose significant public health concerns.

What are some of the unanswered questions for future research directions? And is there anything that you’re particularly excited about in the field of wildfire emissions and air quality?

The exciting thing is that there are so many unanswered questions. So many opportunities exist for people to come in and do some amazing experiments. I am really excited to see what people come up with. I am excited to see the data that emerges from the current laboratory studies. I believe it will greatly inform our work at the EPA, shaping our inventories and guiding public health recommendations regarding smoke protection.

The most important thing is to understand the proper guidance for public health. How should individuals protect themselves? Should they use air cleaners, seek further measures, or evacuate if necessary? Answering these questions hinges on having sufficient information regarding wildfire emissions. Therefore, I am really excited to see what researchers develop over the next few years.

Have you noticed that attitudes are different globally regarding the health aspects of wildland and urban wildlife fires?

Global attitudes are quite different. Unfortunately, I do not really have much experience at the global level. I have read the literature from other areas impacted by wildfires, such as Australia, Portugal, Spain, and Greece, and I like to see what information they examine.

From this, I have noticed a differing focus. Countries are focusing on aspects of wildfires that we haven’t examined as thoroughly in the United States, such as investigating ash fall and gaining a deeper understanding of its composition. We are currently initiating research in the States to delve into this area further.

It is also fascinating to see the variations in wildfire management approaches among different countries. For instance, hazard-reduction fires, which are more common in Australia, are becoming increasingly adopted. Similarly, prescribed burning is now being utilized in California’s high-risk wildland-urban interface areas.

In terms of health effects and toxic emissions response, I haven’t observed many differences across regions. However, within the United States, it’s intriguing to hear people’s perspectives on fires. Many seem to differentiate between wildfire smoke from forest fires and urban fires from houses, perceiving the former as more natural and less harmful. However, there’s often a lack of clear understanding regarding the health impacts of any kind of wildfire smoke. It’s crucial to emphasize the importance of minimizing exposure to wildfire smoke for public health.

As we mark the 75th anniversary of Pittcon, could you share your first memory or experience of attending this conference and how it impacted your view of the scientific community?

This being my first time at Pittcon, I am really just taking it all in. It is quite interesting and different to be at a conference specifically for chemists, run by chemists. I love hearing people dive deep into the details of their triple-quad MSMS. It is amazing to see all of these different experts in action, and I genuinely appreciate their work and how it is helping to enhance my own. It has truly been a fun experience so far.

What are you most looking forward to at Pittcon 2024 in San Diego?

What I am most excited about is the exposition. I always enjoy exploring the floor and discovering what is new. Seeing the latest technologies and shiny gadgets is my favorite part of any conference. I am eager to get my hands on them and try out new measurements with new tools.

One of the best parts is also engaging with people and discussing my own measurement challenges. They often have solutions; if not, they might have one next year. Building these relationships is crucial because we rely on instrument vendors for the tools we need to take measurements.

About Amara Holder

Dr. Amara Holder is a research mechanical engineer with the US Environmental Protection Agency’s Office of Research and Development. Her research focuses broadly on pollutant emissions from combustion sources and their impacts on human health and the environment, with a special focus on wildland fires. Her research has advanced the understanding of the fate of toxic metals in wildland fires, including those that burn in the wildland urban interface. She has also developed technologies to monitor the impacts of wildfire smoke on air quality and evaluated lower-cost methods to reduce smoke exposure. She has received EPA’s highest honor – Gold Medal for Exceptional Service – for contributing to the science to support the AirNow Fire and Smoke map. She is an internationally recognized expert on the emissions from wildland fires and has contributed to multiple scientific assessments on wildfire smoke, including serving as a member of the National Academies Committee on the Chemistry of Urban Wildfires.

This information has been sourced, reviewed and adapted from materials provided by Pittcon.

For more information on this source, please visit Pittcon.

Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.


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