The wildfires blazing across Northern California this week produced the same amount of air pollution as vehicles did in the state in one year, according to Sean Raffuse, an air-quality analyst at the Crocker Nuclear Laboratory at the University of California, Davis.
Raffuse said Thursday that the wildfires burning in Napa, Sonoma and Solano counties have released more than 10,000 tons of PM 2.5.
PM stands for "particulate matter," the term used for a mixture of solid particles and liquid droplets found in the air. PM 2.5 refers to inhalable particles with diameters of 2.5 micrometers or smaller. (PM 2.5 is about 30 times smaller than the average diameter of human hair, which is about 70 micrometers.)
The 10,000 tons of PM 2.5 that have been released is nearly equivalent to estimates of PM 2.5 from on-road vehicles in California for the entire year of 2014, the most recent year for which such data are available.
A comparison can be made between the current quality of air pollution in Beijing and the Bay Area, with the former recorded as 162 PM 2.5 and the latter at 158 PM 2.5.
On Tuesday, the Northern California wildfires led to the worst air pollution ever recorded in the area. The air score in Napa hit an ultimate high of 486: more than two times the "very unhealthy" index for air quality.
However, not all air pollution is created equal, said Michelle L. Bell, a professor of environmental health at Yale University.
The lasting health effects of wildfires
"I would say that the air quality in Beijing and the current air quality due to forest fires are both very poor, but the sources of the air quality are very different," Bell said, noting that wildfire air pollution is different from the kind produced by cars and coal.
"Different types of air pollution can have different impacts on the human body," she said. The source of air pollution affects its chemical structure, and the chemical structure influences how it affects the body. Bell could not say precisely how pollution from fires might affect a person's health differently -- or more potently -- than pollution from cars, say, or factories, only that the chemical interaction with the human body would be unique.
"That's why it's very important to note that we have demonstrated that the air pollution specifically from wildfires is harmful to human health," Bell said.
Exposure to particles from wildfire smoke can cause respiratory troubles including chest pains, a fast heartbeat or an asthma attack.
In a recent study, Bell and her colleagues looked at hospital admissions for an elderly population in the western United States. Specifically, they examined how wildfires impact the risk of hospital admissions for an elderly population: those 65 years and older.
"We found that people were more likely to be hospitalized during and shortly after exposure to wildfire smoke than during other periods," Bell said.
The research, which did not delve into the reasons for each hospitalization, looked at "actual real-world people in real-world pollution," she said.
And the research shows that air pollution from wildfires is detrimental to health in ways beyond "those that immediately die from the wildfires in ways that may be obvious."
In other words, the health consequences from this wildfire smoke will be much larger than we see right now.
Coco Liu, lead author of the study, a former student of Bell's and now a postdoctoral fellow at Johns Hopkins, wrote in an email that "research has found that high increase in fine particulate matter due to wildfire smoke (is) associated with increased risks on acute respiratory admissions."
"Females are more vulnerable to wildfire smoke than males," Liu added, and children are more at risk than adults.
Generally, air pollution is very harmful to infants, with studies showing an increased risk of infant mortality, Bell said. Exposure in the womb to air pollution in general can lead to preterm birth and birth defects. "I would anticipate that wildfire smoke would have an impact on infants," she added.
To protect themselves, people need to reduce their exposure to wildfire smoke, Bell said: "In extreme cases, this may be evacuation, in other cases, this may be staying indoors."
More, hotter wildfires predicted
California consistently ranks high among states with the most polluted cities. This year's State of the Air report from the American Lung Association found that the state had seven of the 10 most polluted metro areas in the country.
Clearly, the wildfires -- with blazes that have scorched more than 190,000 acres, destroyed 3,500-plus structures and killed 31 people -- are not helping. This week's fire is the deadliest in the state's history.
More wildfires will likely be part of California's future due to the Earth's changing climate, Bell said.
"While it is extremely difficult to link any individual incident to climate change," the research indicates that wildfires are "one of the ways in which climate is anticipated to impact our environment and thereby impact human health," she said.
"The science shows that wildfires are anticipated to occur more often, to last longer and to burn hotter."