West coast fires produce east coast effects

Earlier this month, New York City and other cities along the east coast experienced some of the worst air pollution in the world. The cause? Wildfires in California and Oregon so large they produced smoke that drifted thousands of miles. If smoke that dense can travel from one end of the U.S. to the other, imagine what it could do to your lungs.

Scientists can accurately see how far and wide wildfire smoke spreads across an area, but they have a more difficult time predicting whether the plumes are high enough in altitude or lower to the ground where it can gravely affect people's health.

But a team of researchers led by University of Utah chemical engineering associate professor Heather A. Holmes has developed a method of combining a meteorological model with NASA satellite data to determine how high up wildfire smoke is from the ground. That will lead to more accurate predictions of whether and when smoke from a nearby wildfire could reach people on the ground.

"Our hope is this technique gets incorporated into smoke forecasting as a way to improve warning systems related to smoke exposure," says Holmes, whose research is focused on the physics and chemistry of air pollution.

Holmes' research was published in the most recent issue of the Journal of Geophysical Research: Atmospheres. It was co-authored by one of Holmes's former graduate students, S. Marcela Loría-Salazar, who is now an assistant professor at the University of Oklahoma's School of Meteorology.

Before, scientists could not accurately predict whether wildfire smoke would actually reach the lower altitudes of an area where it can affect residents, even by examining satellite data of the smoke's spread. For example, during the 2013 Yosemite Rim Fire in 2013, one of California's largest wildfires that scorched more than 257,000 acres, they initially couldn't explain why Fresno, Calif., had low levels of pollution even though satellite images from the fire showed smoke covering the city. It turns out the mountains created complex winds, and the smoke was actually in the upper level of the troposphere (the lowest region of the atmosphere) where it was separated from the earth's surface.

 So Holmes and Loria-Salazar analyzed satellite data from the Yosemite Rim Fire along with ground observation data and developed a method to better understand the vertical smoke patterns. They examined what is called the "plume injection height" data from the satellite, an estimate of the top layer of the pollution, and the vertical meteorology at the time of the fire. With that, they developed a "smoke height/boundary ratio," an estimate of how much of the smoke is going down to the surface of the Earth. Better understanding where the smoke is in the atmosphere vertically can help scientists also understand where the smoke will be downwind, says Holmes.

"There's a lot of uncertainties in understanding the vertical mixing in the atmosphere, and that really drives where the smoke will end up," she says.

With this new information, Holmes believes meteorologists, climatologists or air quality experts could possibly predict up to two or three days whether smoke from a wildfire could affect the health of residents in a nearby city.

"If you can forecast this, you can make more informed decisions on whether to have school closures, or you can give alerts on when to not go outside to exercise," she says. "You can give people information to protect themselves better."

Wood smoke produces microscopic particulate matter that can penetrate the lungs and adversely affect a person's health, particularly those with lung and heart conditions, diabetes, older adults, younger children and pregnant women, according to the U.S. Environmental Protection Agency. Studies show that wildfire smoke not only affects people while they are outside, but it also seeps into homes and affects indoor air quality.