California, Indonesia, Brasil, Portugal—Wildfires rage worldwide in what seems to be a greater frequency than ever before. In fact, the number of acres burned-up in wildfires across the United States has indeed been increasing since the 1980s.

Number of wildfires over time in the USA
* 2004 fires and acres do not include state lands for North Carolina. 
Source: National Interagency Fire Center.

Within the USA, the state that dealt with the most number of fires last year was Texas, with California coming in second. However, even though Texas saw the greatest number of fires, Californians suffered massive devastation with fires claiming 1,823,153 acres of land—roughly 2,164 times the size of NewYork’s Central Park or 1,381,176 football fields! That’s three times more than those areas lost to fires in Texas that year.

That amount of destruction and environmental impact can seem unmanageable. Going back to our mission at Plume Labs, we believe that by taking the time to understand something as huge and complex as this and really drilling into the facts, it’s possible to find solutions to the most challenging problems. To make sure we are living up to this mission, we’re continuously running experiments, both in the lab and out. Working with our data, devices and community members to make sense of ongoing issues is a great part of the job, and sharing the results is even better. 

To start understanding the fires in California (and around the world), I sat down with our chief atmospheric scientist (Dr. Boris Quennehen), our lead data scientist (Grégoire Jauvion), and Dr. Jonathan Tan from the Philadelphia Children’s Hospital to take a closer look at what actually happens to the air in and around these colossal fires and what impact the associated air pollution has on the people breathing it. 

Our main goal was to figure out a few things: 

  1. How bad does the air actually get during a wildfire?
  2. What kind of pollutants are in wildfire smoke?
  3. What are the health impacts of wildfire smoke exposure?
  4. What can we do to protect our lungs?

To kick things off, I asked Gregoire to take me through the nuts and bolts of wildfire smoke. How bad does it get? How does it move around?  Going hyper-local: How bad does the air actually get during a wildfire?

1. Going hyper-local: How bad does the air actually get during a wildfire?

Grégoire studied computer science and applied mathematics, and has extensive experience in building AI products in various sectors. He is now working on the Plume Labs  air quality data platform, ingesting terabytes of atmospheric data using state-of-the-art methods.

So just what happens in the air during a wildfire? This is an important question to answer because by understanding how the air and the pollution it carries changes and moves during a wildfire, it’s possible to take steps to protect your lungs. 

To answer my question, Grégoire started by analyzing the data from monitoring stations around the San Francisco Bay Area for 2018. He put the results into context for me by using the Plume Air Quality Index (based on the WHO pollution exposure thresholds). This AQI helps us quickly tell how long it is before we start to have negative health effects from poor air quality, 

Here’s how the numbers breakdown into Plume AQI thresholds—the lower the number, the longer you can safely breathe the air:

  • 0-20 Low Pollution – no limit, no worries. Pollution levels are under the recommended exposure thresholds set by the World Health Organisation (WHO) for one year of pollution exposure. 
  • 21-50 Moderate Pollution – 1 year. Air quality is considered acceptable, though over the recommended threshold for one year. 
  • 51-100 High Pollution – 24 hours. The air is highly polluted—above twenty-four-hour exposure recommendations.
  • 101+ Very High Pollution and above – 1 Hour. Pollution levels have exceeded exposure threshold for one hour.

Keeping the Plume AQI thresholds in mind, here is what Gregoire had to say about his investigation:

Grégoire – Looking at our historical data for the San Francisco Bay Area, I was able to determine that the annual average of PM2.5 over all the monitoring stations in the area is 24 on Plume AQI (Moderate). This means that you might start having health problems after a year of exposure, but don’t panic Bay Area friends! It’s important to keep in mind that this is the area-wide average level of outdoor pollution. 

We know that air quality varies dramatically from street to street, and even room to room indoors. Depending on where you live and what your daily routine is, your exposure levels may be higher or lower than the average. 

San Francisco Bay Area ground based monitoring stations

Tracking your personal exposure (indoors and out) with a personal pollution sensor like our Flow and Flow 2 can help you figure out what you’re being exposed to, and where. In fact, the University of King’s College in London recently released a study showing that with the right information, people were able to make informed day-to-day decisions related to air quality and reduce their exposure by 50 percent.

In any case, after establishing this average, I started to look at the data during the 2018 Campfire crisis. I found that the levels of PM2.5 at the monitoring stations most impacted by the fire skyrocketed to 300+ on the Plume AQI! This definitely made the air toxic and launched it into the crisis category. Check out the graph below.

Data from SF stations: the light grey line are individual stations and the black line is the mean. The Camp Fire period is highlighted in red. 

These readings are astonishing but it’s important to consider that analyzing only data from air quality monitoring stations has limitations. Air quality varies a lot in space (e.g. difference between a busy road and a park nearby) and in time (a heavy rain can make air pollution disappear in a few hours). 

The main limiting factor is the lack of ground-based monitoring stations and, as I mentioned before, they are fixed in one place and there are not enough of them. There are only a few dozen in a large region like the Bay Area, for example.

To solve this problem, we use mathematical models that draw on lots of different data sources (including from monitoring stations) to fill in the gaps and build air quality forecasts at a very fine granularity.

For example, our models are largely based on satellite measurements and detailed assumptions about the main air pollution emission sources—traffic, industry, or energy production. 

PM2.5 from the 2018 Camp Fire crisis in California

In the particular case of a wildfire, we make sure our forecasts simulate where the fire is and how it’s changing — growing, shrinking, moving, and so on.

Grégoire’s investigation and explanation of how bad the pollution gets in and around wildfires, and how he and his team track and measure air quality, set the stage for my round of questions about the make-up of wildfire smoke. 

Dr. Quennehen took up the challenge of breaking things down for me in the next section. 

2. The breakdown: What kind of pollution do wildfires create?

Dr. Boris Quennehen studied the composition of anthropogenic and forest fire pollution plumes transported from mid-latitudes to the Arctic. His work shows that processes affecting particle size and concentration are still active after several days of transport in the atmosphere.

Dr. Boris Quennehen studied the composition of anthropogenic and forest fire pollution plumes transported from mid-latitudes to the Arctic. His work shows that processes affecting particle size and concentration are still active after several days of transport in the atmosphere.

The particulars of particulates

Dr. Quennehen: Like any combustion process, wildfires emit a mixture of particulate matter (PM) and gases. A 2013 study showed that the PM chemical composition and gas types/concentrations varies depending on the materials burning. In particular, forest fires emit significantly more pollutants, mostly because they last longer. However, urban fires are more likely to emit a higher percentage of toxic gases due to plastic or mineral oil burning. 1

In the case of a wildfire, a lot of dead and standing trees get burned up, along with other biomass like dry grasses. Even variations of wood and how it is burning can make a difference. For example, a recent study of wildfire smoke in California found that smoke coming from a smouldering, smoky fire with little visible flame is more damaging than smoke coming from a really bright, intense flaming fire!

What exactly is PM?

What is it? Particulate matter consists of small solid particles that can penetrate the airways and lungs. The finest particles can even bind to blood vessels. PM10 (PM standing for particulate matter) refers to particles smaller than 10 microns in diameter and PM2.5 for those smaller than 2.5 microns. To give you an idea of how small that is, think about one hair from your head. The average human hair is about 70 micrometers in diameter. PM1 are nano-particles and really tiny, measuring less than 1 micron. 

Particulate Matter Image source: EPA

Where does it come from? Particulate matter comes from human activity such as road traffic or energy transformation and from natural phenomena such as volcanic eruptions and even sand on a windy beach. The PM concentration in the air varies significantly with elements like temperature and wind speed. 

What are the risks? Fine particles trigger nasal allergies. Chronic exposure is a risk factor for cardiovascular and respiratory diseases as well as lung cancer. 

What is most concerning, in terms of health, is the size of the particles. Most of the particulate matter is made up of the very tiny PM 2.5 and even smaller nano-particles or PM1 and the smaller the particulate, the more dangerous it is. But more on that later from Dr. Tan. 2

Not only is particulate matter of this size dangerous, but it also gets around. Fine particles like PM2.5 and PM1 remain in the atmosphere longer and travel extraordinary distances (e.g., from Quebec to Baltimore). 3, 4

For example, Particulate matter from the 2017 fires in California were transported up the east coast (more than 3000 miles away from source). When we are considering that enormous distance, pollution usually remains at high altitude. However, for this specific event, the pollution dropped down to a lower altitude and was even detected in Iowa. Thankfully, pollution from the California fires in 2018 and 2019 moved over the ocean most of the time, predominantly affecting the region between source and the ocean.

But what about the gases, you say?

Dr. Quennehen discovered some really interesting information about gasses in his research. Emissions of NO2 and SO2 are present in wildfire smoke but in lower concentrations than fossil fuel combustion. However, emissions of volatile organic compounds (VOCs) are actually higher.

Let’s take a look at each gas one by one so we can get a good idea about what they are, where they come from and what effects they have on our bodies.

Sulfur Dioxide (SO2)

What is it? SO2 or Sulfur Dioxide is an invisible gas and has a nasty, sharp smell. It reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.

Where does it come from? About 99% of the sulfur dioxide in air comes from human sources. The main source of sulfur dioxide in the air is industrial activity that processes materials that contain sulfur, eg the generation of electricity from coal, oil or gas that contains sulfur. Some mineral ores also contain sulfur, and sulfur dioxide is released when they are processed. In addition, industrial activities that burn fossil fuels containing sulfur can be important sources of sulfur dioxide. There are natural sulfur dioxide emissions, but are not common. In particular, volcanic eruptions release massive amounts of sulfur dioxide.

What are the risks? Sulfur dioxide affects human health when it is breathed in. It irritates the nose, throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the chest. The effects of sulfur dioxide are felt very quickly and most people would feel the worst symptoms in 10 or 15 minutes after breathing it in.

Nitrogen Dioxide (NO2)

What is it? NO2 is a suffocating and irritating gas that can be easily recognized thanks to its red-brown color. It also has a pungent odor.

Where does it come from? The main source of nitrogen dioxide (99%) is the burning of fossil fuels: coal, oil and gas. Some nitrogen dioxide can be formed naturally in the atmosphere by lightning and by plants, soil and water. However, only about 1% of the total amount of nitrogen dioxide found in our cities’ air is formed this way. 

What are the risks? The main effect of breathing in raised levels of nitrogen dioxide is the increased likelihood of respiratory problems. Nitrogen dioxide inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis.

Volatile Organic Compounds (VOCs)

What are they? VOCs are compounds that are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects.

Where do they come from? VOCs are released from burning fuel such as gasoline, wood, coal, or natural gas. They are also released from many consumer products like cleaners, hand sanitizers, and beauty products.

What are the risks? The health effects from short term exposure to VOCs may be: Irritation of the eyes and respiratory tract; headaches; dizziness; visual disorders; and memory problems. 

Longer term exposure effects may include: Irritation of the eyes, nose, and throat; nausea; fatigue; loss of coordination; dizziness; damage to the liver, kidneys, and central nervous system; cancer.

After working through the question of what’s actually in the smoke caused by wildfires, I feel like we have the right information to build on. All things considered, I have the strong impression you don’t want to be breathing this toxic combination! But I want to be more specific. What do these pollutants do to our health? To get to the bottom of this, I posed the question to Dr. Jonathan Tan from the Philadelphia Children’s Hospital.  

3. What are the health impacts of wildfire smoke exposure?

Jonathan M. Tan, MD MPH MBI is a Pediatric Anesthesiologist and Assistant Professor of Anesthesiology and Critical Care at the Children’s Hospital of Philadelphia and the University of Pennsylvania. Jonathan’s research has focused on the use of spatial analytics to understand the social, economic and environmental impacts on the health of patients.

The WHO and Plume AQI talk about negative health effects caused by air pollution, but what are these effects? How serious is the situation? Dr. Jonathan Tan has been working around the world to help people with respiratory issues and knows the dangers of pollution entering the lungs.

Dr. Tan: Wildfire smoke exposure can have very real health consequences. The most common health risks associated with smoke exposure are found within our lungs, the major organ of the respiratory system. Smoke exposure can lead to difficulty with breathing, including coughing, runny nose, bronchitis, wheezing and exacerbation of chronic diseases such as asthma and chronic obstructive pulmonary disease (COPD). 

In my experience working in hospitals around the world, smoke exposure also increases in the use of emergency department, hospitalizations and need for medications during wildfire disasters. This has an impact across almost all aspects of patient care. 

It is also important to consider that some populations are more affected by smoke exposure. 

Health effects may be exacerbated if you:

  • Have heart or lung disease (e.g., congestive heart failure, angina, chronic obstructive
  • pulmonary disease, emphysema, asthma)
  • Are an older adult (especially if you have heart or lung disease)
  • Are pregnant.
  • Are a smoker.
  • Are a child. Smoke can be more harmful to children because their respiratory systems are still developing, they breathe in more air than adults, and they are more likely to be active outside.
  • Are involved in strenuous outdoor work or outdoor sports.

In these vulnerable groups, the risk of illness and even death can be much higher than for healthy adults. In addition to respiratory disease, other health risks from wildfire smoke exposure have been associated with risks to the cardiovascular system, the eyes, the neurologic system and adverse mental health outcomes.  

The threat to health from smoke inhalation are from breathing fine particulate matter that are byproducts of the wildfire. The smaller the particulate matter is, the deeper into our bodies the particles can get—causing irritation and inflammation of the airways.  For example, PM2.5 has been found to be highly associated with increases in emergency room visits during wildfires. Smaller particulate matter, such as PM1 could be even more hazardous to health but current research has been lacking due to the limited methods available to study very small particulate matter exposure on the individual level. 

Health impacts can be over the short and long term. While we know much about the health risks of smoke exposure, there is so much more that we do not know. We need to get better at measuring and describing individual exposure to air quality changes. Understanding both outdoor and indoor air quality changes, as well as measuring small particulate matter exposure, will help us better care for individuals and the health of populations exposed to wildfire disasters. 

4. Taking Action: What can we do to protect our lungs?

Even with all the information we have on wildfire-related air pollution, the question remains: What can I do to breathe fresh air in a crisis? Even if you are not in the immediate area of a fire, pollution travels and as we have seen, poor  air quality is a major health threat. 

Here are some actions you can take to reduce your exposure to the airborne particles caused by wildfires:

  • Keep up-to-date with air pollution levels in your area. You can use the AIR report app (iOS / Android) or website for live and forecast air quality information to help you make informed decisions on when to stay inside and when to get out for some exercise or air out your home. In fact, the British Columbia Centre for Disease Control’s (BCCDC) review of five air sampling studies that modeled residential building infiltration efficiencies suggests that staying indoors can be effective at reducing wildfire smoke exposure. 
  • Know where your local clean air home or centres are located. Spread the word and help others find fresh air pockets.  
  • Create your own fresh air refuge with air purifiers. Portable or fixed point air purifiers can be effective in cleaning the air in a wildfire situation but it is important to know the facts before you set out to buy. The  BCCDC has an excellent primer on air purifiers to help you get the basics.
  • Track your exposure—indoors and out. Studies have shown that air quality can vary dramatically from street to street, room to room. Having the right air quality information at the right time has been proven to help people reduce their exposure by up to 50%. We designed Flow 2 to track the most pollutants on the market (even PM1) indoors and out.  
  • Wear a mask. A good pollution mask can help protect you from the dangerous particulate matter pumped into the air by wildfires. Make sure you get something with a filtration capacity rated at least N95. Fit is also crucial. It doesn’t matter how efficient the material is at removing particles from the air if it leaks. Leaky masks don’t help and masks are particularly leaky on children—even causing more problems than good. In fact, the Centers for Disease Control and Prevention’s National Institute for Occupational Safety and Health does not certify any childrens’ respirator masks.Check out this article from the LA times for more info. 

The Department of Homeland Security also has some excellent resources for protecting yourself and your loved ones if you’re ever in a situation that goes beyond the impacts of air pollution. If you find yourself in an area being evacuated, having a plan, staying informed and acting fast when the time comes can save lives. Please visit for complete details.


I started out with four questions I wanted answered:

  1. How bad does the air actually get during a wildfire?
  2. What kind of pollutants are in wildfire smoke?
  3. What are the health impacts of wildfire smoke exposure?
  4. What can we do to protect our lungs?

In going through the process with Gregoire, Dr. Quennehen and Dr. Tan, I think I answered these questions and beyond. The incredible levels of pollution in wildfire smoke and the toxic cocktail of gases and particulate matter is shocking.

Jonathan’s experience with the disastrous health outcomes related to pollution exposure was helpful in putting the impacts on personal health into perspective. As the scientific community learns more about the effects of nano-particles on human health, I’m in no doubt that I’ll be hearing from him in the future with updates to the article.  

Finally, I was impressed at the number of thoughtful resources for people looking for help in preparation for, in the midst of a crisis, or recovering and rebuilding after a fire. I hope this article and our tools can be counted among them.

If you have questions or would like further information, please let us know in the comments, or by contacting the team at


1. Urbanski, S. P.: Combustion efficiency and emission factors for wildfire-season fires in mixed conifer forests of the northern Rocky Mountains, US, Atmos. Chem. Phys., 13, 7241-7262,, 2013. 

2. Makkonen, U., Hellén, H., Anttila, P., & Ferm, M. (2010). Size distribution and chemical composition of airborne particles in south-eastern Finland during different seasons and wildfire episodes in 2006. Science of The Total Environment, 408(3), 644–651. doi:10.1016/j.scitotenv.2009.10.050

3. Kinney, P. L. (2008). Climate Change, Air Quality, and Human Health. American Journal of Preventive Medicine, 35(5), 459–467. doi:10.1016/j.amepre.2008.08.025.

4. Sapkota, A., Symons, J. M., Kleissl, J., Wang, L., Parlange, M. B., Ondov, J., … Buckley, T. J. (2005). Impact of the 2002 Canadian Forest Fires on Particulate Matter Air Quality in Baltimore City. Environmental Science & Technology, 39(1), 24–32. doi:10.1021/es035311z

5. Mauderly, J. L., Barrett, E. G., Day, K. C., Gigliotti, A. P., McDonald, J. D., Harrod, K. S., … Seilkop, S. K. (2014). The National Environmental Respiratory Center (NERC) experiment in multi-pollutant air quality health research: II. Comparison of responses to diesel and gasoline engine exhausts, hardwood smoke and simulated downwind coal emissions. Inhalation Toxicology, 26(11), 651–667. doi:10.3109/08958378.2014.925523

Join the conversation! 3 Comments

  1. Really informative read! Prolonged exposure to wildfires can also damage the macrophage. It is responsible for removing foreign particles from lungs. So, wildfires can also make you more prone to COVID-19.


  2. […] تم العثور على المخاطر الصحية الأكثر شيوعًا المرتبطة بالتعرض للدخان داخل الرئتين ، وفقًا للدكتور جوناثان تان من مستشفى فيلادلفيا للأطفال أخبر Plume Labs في مقابلة عام 2019. […]



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

About Plume Labs

We're here to help you understand what you breathe and take meaningful action against air pollution.


Non classé