YSM Issue 94.1

FOCUS
Environmental Science
UP IN
FLAMES
Retrieving clues about air pollution from forest fires
BY ANAVI UPPAL
Orange skies and choking smoke
covered California last summer.
Wildfires aren’t rare in this state,
but climate change has been making them
increasingly severe—2020 was the worst
Californian wildfire season on record. Recent
research on wildfire patterns can offer insight
into what kinds of pollutants they release into
the atmosphere and may tell us more about
how they impact our health and our planet.
Researchers from the Department of
Chemical and Environmental Engineering
at Yale University found that forest fire
emissions evolve in surprising ways over
time. Associate professor Drew Gentner
and his lab focus on studying air quality
and atmospheric chemistry, particularly
the chemical transformations that organic
compounds undergo in the atmosphere, and
what their ultimate impact might be. The
Gentner lab collaborated with Environment
and Climate Change Canada to take part in a
flight campaign that focused on studying oil
sands emissions in Canada.
The team’s goal was to sample a
forest fire’s emissions to study how the
composition of its smoke plume evolved
over time and distance. “Forest fires are an
important factor in global air quality and
the air quality of local regions, so the field
is conducting more and more projects to
study wildfire smoke,” Gentner said.
Catching Fire
The flight campaign—an airplanebased
measurement program—was
initially focused on studying oil
sands emissions and not forest fires.
But when a forest fire coincidentally
erupted during the campaign, a plane
was quickly dispatched to sample its
emissions. “I think it was in the back of
their mind that, if this happens, we're
going to go, and once they heard about
it they capitalized on the opportunity,”
said Jenna Ditto, a former doctoral
student at Yale in the Gentner lab. “This
type of sampling definitely needs quick
thinking, and you have to be ready.”
The aircraft flew in zig-zag lines called
transects along the emission plume as
it traveled downwind and sampled it in
five different places. Sample one was
taken closest to the fire, while sample
five was the farthest. The farther that the
sample was from the wildfire, the older
those emissions were.
The plane was outfitted with
instrumentation that measured gases,
particles, and weather conditions in
real time, while also collecting offline
samples for later laboratory analysis.
These offline samples were collected on
small filters or glass tubes filled with
absorbent materials that trap a mixture
of compounds from the atmosphere.
Once collected, the samples were
frozen at around negative thirty degrees
Celsius to prevent chemical reactions
from altering them during storage. When
the team did an initial compound class
analysis to see what materials they were
dealing with, they found a surprising
result: the quantity of compounds
called CHONS—which contain carbon,
hydrogen, oxygen, nitrogen, and sulfur—
increased in particle-phase samples taken
the furthest from the forest fire. “We saw
that and thought: that's very interesting,
we've never seen this before. Why is
that happening? Let’s look more into the
functional groups,” Ditto said. Compound
class analysis is usually done as just a first
step to get a sense for what the data looks
like, but it fortuitously led the team to
some interesting results.
12 Yale Scientific Magazine March 2021
www.yalescientific.org