In recent years in the US — and especially in the last couple of weeks — smoke has turned the sky hazy across a large swath of the US from wildfires, and a lot of people are wondering what’s in the air they’re breathing.
As an environmental toxicologist, I study the effects of wildfire smoke and how they differ from other sources of air pollution. We know that breathing wildfire smoke can be harmful, but less clear is what the worsening wildfire landscape will mean for public health in the future, but research is raising red flags.
In parts of the West, wildfire smoke now makes up nearly half the air pollution measured annually. A study by the California Air Resources Board found another threat: High levels of lead and other metals turned up in smoke from the 2018 Camp Fire, which destroyed the town of Paradise, California. These findings suggest smoke from wildfires could be even more dangerous than originally thought because of the building materials that burn in them.
Here’s a closer look at what makes up wildfire smoke and what you can do to protect yourself and your loved ones.
What’s in wildfire smoke?
What exactly is in a wildfire’s smoke depends on a few key things: what’s burning (grass, brush, trees, etc.); the temperature (is it flaming or just smoldering?); and the distance between the person breathing the smoke and the fire producing it.
Smoke from wildfires contains thousands of individual compounds, including carbon monoxide, volatile organic compounds, carbon dioxide, hydrocarbons and nitrogen oxides. The most prevalent pollutant by mass is particulate matter less than 2.5 micrometers in diameter, roughly 50 times smaller than a grain of sand. (Its prevalence is one reason that health authorities issue air quality warnings using PM 2.5 as the metric.)
As mentioned above, the study on smoke from the Camp Fire found dangerous levels of lead in smoke blowing downwind as the fire burned. The metals, which have been linked to health harms including high blood pressure and developmental effects in children with long-term exposure, traveled more than 150 miles on the wind, with concentrations 50 times above average in some areas.
Distance affects the ability of smoke to “age”, meaning to be acted upon by the sun and other chemicals in the air as it travels, and aging can make it more toxic. Importantly, large particles — like what most people think of as ash — do not typically travel that far from the fire, but small particles, or aerosols, can travel across continents.
What does wildfire smoke do to human bodies?
There’s another reason PM2.5 is used to make health recommendations: It defines the cut off for particles that can travel deep into the lungs and cause the most damage.
The human body is equipped with natural defense mechanisms against particles bigger than PM2.5. As I tell my students, if you’ve ever coughed up phlegm or blown your nose after being around a campfire and discovered black or brown mucus in your tissue, you have witnessed these mechanisms firsthand.
But the really small particles can bypass these defenses and disturb the air sacs where oxygen crosses over into the blood. Fortunately, we have specialized immune cells present called “macrophages”. It’s their job to seek out foreign material and remove or destroy it. However, studies have shown that repeated exposure to elevated levels of wood smoke can suppress macrophages, leading to increases in lung inflammation.
When it comes to smoke exposure, dose, frequency and duration are important. Short-term exposure can irritate the eyes and throat, while long-term exposure to wildfire smoke over days or weeks can raise the risk of lung damage and may also contribute to cardiovascular problems. Considering that it is the macrophage’s job to remove foreign material — including smoke particles and pathogens — it is reasonable to make a connection between smoke exposure and risk of viral infection.
What can you do to stay healthy?
Here’s the advice I would give just about anyone living downwind from a wildfire:
- Stay informed about air quality by identifying your best local resources for air quality alerts, information about active fires, and recommendations for better health practices.
- If possible, avoid being outside or doing strenuous activity — like running or cycling — when there is an air quality warning for your area.
- Be aware that not all face masks protect against smoke particles. Most cloth masks will not capture small wood smoke particles. This requires an N95 mask that fits and is worn properly. Without a proper fit, N95s do not work as well.
- Establish a clean space. Some communities in Western states have offered “clean spaces” programs that help people take refuge in buildings with clean air and air conditioning. At home, a person can create their own clean and cool spaces using a window air conditioner and a portable air purifier.
- The US Environmental Protection Agency also advises people to avoid anything that contributes to indoor air pollutants. This includes vacuuming that can stir up pollutants, as well as burning candles, firing up gas stoves and smoking.
Megafires are on the rise. So what steps can we take to avoid further destruction? Forest ecologist Paul Hessburg explains how we can help restore natural balance in this Talk: