Most of the US population (67%) across every state in the continental US, except for Georgia and South Carolina, experienced at least one day of heavy- or medium-density wildfire smoke last month, according to a new analysis by Direct Relief’s research and analysis team of data from the National Oceanic and Atmospheric Administration.

Over the same period, an estimated 28.6 million people, or nearly 9 percent of the US population, experienced one or more days of heavy smoke.

According to NOAA, medium and heavy smoke density refers to the thickness of smoke observed in satellite imagery. Medium smoke density is meant to approximate between 10-21 micrograms per cubic meter, and heavy smoke density is intended to approximate 21-32 micrograms per cubic meter.

Broad exposure to smoke from wildfires has occurred despite this year seeing the fewest acres burned since 2014.

Last month alone, an estimated 1.44 million people across the US experienced seven or more days of heavy-density wildfire smoke.

Most locations that have endured such conditions over the past month are in Alaska, with Fairbanks being the most populous, though areas in California, Montana, and Idaho have been subject to at least seven high-density smoke days.

Though often associated with western US states, several Midwest and eastern states have also experienced at least one heavy smoke day, including vast swaths of Minnesota and Iowa as well as regions of New York and Pennsylvania.

Several studies have shown a link between wildfire smoke events and “significant” increases in hospital emergency department visits, especially for respiratory and cardiovascular ailments. These increases, particularly related to asthma and respiratory diseases, as well as cardiovascular diseases, can begin within a day or two of the events and continue for several weeks or more afterward, according to Helene G. Margolis, Ph.D., a professor in the Department of Internal Medicine at UC Davis Children’s Hospital.

“Children, people with preexisting chronic diseases, and children in utero are definitely susceptible, across the life course,” Margolis said about people exposed to extended periods of either wildfire smoke or traffic-related pollution.

Some medical conditions associated with repeated exposure include respiratory diseases, deficits in lung function, asthma, allergies, chronic obstructed pulmonary disease, and altered immunology.

After prolonged exposure to traffic-related pollution, decreased lung function has also been reported in children.

“You can almost certainly expect that wildfire smoke is contributing to that,” Margolis said.

Wildfire smoke exposure can also lead to a higher risk of contracting Covid-19 and other illnesses since wildfire smoke and air pollution can “alter the efficacy of immune response,” Margolis said.

Both wildfire smoke and air pollution can trigger inflammation in a person’s airways, causing elevated inflammatory markers to occur throughout the body, she said, which can be particularly dangerous to people with metabolic syndrome.

smoke hits differently

Though smoke blankets an area, it does not affect all people in that area equally. Key differentiating factors include where a person lives, including the ability to either seal their home or leave, underlying health conditions, and financial circumstances, including the ability to buy air filters and avoid outdoor work.

“Some studies have shown that more vulnerable populations may experience a larger impact for the same event,” said Jennifer Richmond-Bryant, Ph.D., a professor at North Carolina State University’s College of Natural Resources, noting that not all vulnerable populations are the same.

As one example, focusing on non-medical factors, Richmond noted having air conditioning can “make a big impact.”

“As climate change progresses, there are not only more fires, but those with the means can close up their homes [during a wildfire smoke event]. Without air conditioning and with 90-degree heat, you’re going to have to open your windows,” Richmond-Bryant said.

While both traffic-related air pollution and wildfire smoke can carry serious risks, wildfire smoke carries unique risks owing to its compositions, which vary based on a range of factors, including where and what it is burning and how it acts in the atmosphere.

“Wildfires are occurring with substantially higher concentrations of particulate material than regular ambient air pollution,” Richmond-Bryant said.

“A lot of locations with older growth forests were around in the days of leaded gasoline. You might have wood with trace amounts of lead. Or they might have been around during a time of coal power, more than we have now, meaning mercury may have been embedded,” she said.

In addition to natural materials, Richmond-Bryant and Margolis said that human-made materials can also increase the toxicity of wildfire smoke – an increasing problem as people continue to move into formerly undeveloped, forested areas.

“A mid-20^th century house might have lead paint and become part of the air combustion mixture. You also have a lot of plastic materials,” Richmond-Bryant said.

“Those chemicals carry much higher toxicity risk,” said Margolis about plastics and other human-made materials.

A study on the 2018 Camp Fire showed that its smoke contained “dangerous” and “concerning” levels of particulate matter and toxic metal contaminants, including lead, “which spiked for about 24 hours.”

Margolis said that issues around wildfire smoke figure to increase due to climate change and other ongoing trends.

“Given climate change and the drying of the landscape, the conditions have become increasingly arid. When you factor in more things like forestry management, these events are happening earlier, they last longer, there’s more fuel, so the magnitude, length, and the duration of exposure to wildfires is greater,” Margolis said.

“It’s going to have downstream consequences,” Margolis said.

Direct Relief has been responding to wildfires for decades and most recently shipped dozens of requested emergency field medic packs to the California National Guard to support their response to the ongoing wildfires in northern California. Each pack is equipped with triage and medical essentials, including infection control supplies, trauma care, diagnostics, and PPE.

Michael Robinson, Crisis Mapping and Data Science Specialist at Direct Relief, contributed to this article.