Study Finds Wildfire Smoke More Dangerous To Humans Than Car Pollution

The devastating effects of wildfires have been well documented. Forests, homes, and businesses destroyed, billions of dollars lost. In fact, in 2018 alone, California’s top three wildfires year exceeded $10 billion U.S. in financial losses.

But, there’s another price we pay for wildfires… one that is far more catastrophic than even the immense physical and financial losses… our health.

The study

Researchers with the Scripps Institution of Oceanography at the University of California, San Diego looked at hospital admissions data over 14 years in Southern California and compared the data to spikes in air pollution during strong wind events. They found that pollutants from wildfire smoke caused up to a 10% increase in hospital admissions.

And the problem is not limited to California. An NPR analysis of air quality on the West Coast found that 1 in 7 residents experienced at least one day of unhealthy air conditions last year. For weeks, the smoke was so thick in parts of Oregon, Washington and California that public health officials urged people to stay indoors and avoid physical activities. 

What makes wildfire smoke so dangerous?

While all smoke can cause health problems, wildfire smoke is particularly dangerous because of the toxic mix of pollutants it carries.  What exactly is in the smoke depends on a few things:

  • what’s burning
  • the temperature
  • the distance between the person breathing the smoke and the fire producing it.

As the fires tear through towns, homes, and forests, they pick up a variety of pollutants including carbon monoxide, volatile organic compounds (VOCs), carbon dioxide, hydrocarbons, and nitrogen oxides. It’s the tiniest of these particles, known as Particulate matter, that are the most dangerous.

What are Particulate matter?

Particulate matter are a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. 

PM are usually classified as particulate matter, fine particles, or ultrafine particles. 

PM 10 (particulate matter) are inhalable particles, with diameters that are generally 10 micrometers and smaller. 

PM2.5, also known as fine particles, are those that are smaller than 2.5 micrometers in diameter. PM2.5 are about 30 times smaller than a human hair. 

Ultrafine Particles (UFP) are particulate matter that are less than .1 microns in diameter. 

Exposure to any particulate matter can cause health issues, but fine and ultrafine particles are the most dangerous. 

What makes Fine and ultrafine particles so dangerous?

Because PM2.5 and ultrafine particle matter are so small, they are easily inhaled and are able to penetrate deep into your respiratory system. 

One recent study called PM 2.5 “the largest environmental risk factor worldwide,” responsible for many more deaths than alcohol use, physical inactivity or high sodium intake. In fact, 4.2 million people die every year from breathing in large amounts of fine and ultrafine particulate matter. 

Unfortunately, wildfires are a major source of PM 2.5. The University of California study found that the tiny particles released in wildfire smoke are up to 10 times more harmful to humans than particles released from other sources, such as car exhaust.

Who needs to be worried about wildfire smoke?

Obviously, those who are in closest proximity to the fires need to be most concerned. 

The Environmental Protection Agency recommends the following guidelines for fire safety:

  • If there is an active fire in your area and it is very close to your house: It may be best to evacuate. Fires can spread quickly and the smoke plume can make it difficult to see in an evacuation. In addition, it can be nearly impossible to keep dense smoke from building up in the indoor air. Pay close attention to local emergency alerts to know when to evacuate.
  • If there is an active fire close enough to cause high smoke levels, but the fire is not threatening your home:Smoke may enter your home, making it harder to breathe. Learn more about what to do in this situation and how to prepare for it. If there is an active fire in your area, follow your local news, EPA’s AirNow website, or your state air quality website for up-to-date information.
  • You may hear that smoke from a far-away wildfire has spread to your community, even if it is thousands of miles away. While this can happen, the amount of smoke that may reach your community from such a distance is probably very small, and may be overshadowed by local sources of particle pollution. In this situation, you can monitor your local outdoor air quality on and manage your indoor air quality as you normally would.

But, while those who are closest to the fire face the most dire circumstances, unfortunately, we ALL need to be concerned about wildfire smoke. Because of their tiny size, fine and ultrafine particles can travel great distances. In fact, California wildfire smoke has been detected 3,000 miles away in New York City. That red, hazy sun you’ve been noticing may be pretty, but unfortunately, it’s a sign that dangerous wildfire pollutants have traveled to your area.

And that particulate matter does not stay outdoors. No matter how tightly sealed your home is, particles can still enter indoor spaces through doors, windows, and “leakiness” in building structures.

What can we do to lessen our exposure to wildfire smoke?

Monitor Local Smoke Warnings

Even if you think that your home is far enough away from the wildfires to be of concern, it’s always important to check your local air quality and pay attention to any smoke warnings on the local news.  provides free air quality monitoring each day.

Keep windows and doors closed

Most of the time indoor air actually contains two to five times more pollutants than outdoor air.  But, during a wildfire, the situation changes. Keeping windows and doors shut tightly can minimize the smoke that enters your home. It also helps to limit the number of times you enter and exit your home.

Use the right air conditioner

Unfortunately, the wildfires have coincided with a blistering heatwave.  AC’s can be useful in both keeping your home cool and lowering indoor smoke.  When running an AC, make sure the filter is clean and that any “fresh air” settings that bring in air from the outdoors are disabled. Don’t use ACs that rely on outdoor air.

Avoid activities that cause more indoor pollution including:

  • Smoking cigarettes.
  • Using gas, propane, or wood-burning stoves and furnaces.
  • Spraying aerosol products.
  • Frying or broiling food.
  • Burning candles or incense.
  • Vacuuming, unless you use a vacuum with a HEPA filter.

Purchase an air purifier with a True HEPA filter.

The particles in wildfire smoke are generally between 0.4 and 0.7 microns. True-HEPA air filters are exceptionally good at removing particles of that size from the air. In fact, the EPA recommends that residents in areas vulnerable to wildfires purchase an air purifier before a fire emergency occurs. Because wildfire smoke is made up of many different hazardous pollutants, be sure to look for high-quality air purifiers that are equipped to deal with gasses and volatile organic compounds (VOCs).

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