SPLAT II provides measurements of particles with unprecedented sensitivity and precision to scientists such as Alla Zelenyuk. |
Airborne
gases get sucked into stubborn smog particles from which they cannot
escape, according to findings by UC Irvine and other researchers
published today in the Proceedings of the National Academy of Sciences.
The
results could explain a problem identified in recent years: Computer
models long used by the U.S. Environmental Protection Agency, California
air regulators and others significantly underestimate
organic aerosols—the major component of smog particles. Such pollution
blocks views of mountains and has been linked to everything from asthma
to heart attacks. It is also the largest unknown in climate change
calculations.
“You
can’t have a lot of confidence in the predicted levels right now,” said
lead author Veronique Perraud, assistant project scientist to
pioneering UCI air chemist Barbara Finlayson-Pitts. “It’s extremely
important, because if the models do a bad job of predicting particles,
we may be underestimating the effects on the public.”
An independent expert who reviewed the research for PNAS agreed.
“The
conclusions are highly significant,” said Purdue University atmospheric
chemist Paul Shepson. “This paper should—and, I expect, will—have a big
impact. We’ve known for nearly a decade that there’s a huge difference
between what’s in the models and what’s actually in the air. Thanks to
this paper, we have a much better idea of why.”
Scientists
at UCI, a U.S. Department of Energy laboratory and Portland State
University combined pinene, a common ingredient in household cleaners
such as Pine Sol and outdoor emissions, with oxides of nitrogen and
ozone to mimic smog buildup.
Models
used by regulators for decades have assumed that organic aerosols in
such pollution form liquid droplets that quickly dissolve potentially
unhealthy gases. But the new work found that once gases are sucked into a
particle, they get buried deeper and deeper.
“They
check in, and they don’t check out. They cannot escape. The material
does not readily evaporate and may live longer and grow faster in total
mass than previously thought,” Finlayson-Pitts said. “This is consistent
with related studies showing that smog particles may be an extremely viscous tar.”
Perraud
noted that broader study needs to be done: “The next logical step is to
straighten the models out. We need enough follow-up data to do so.”
Sophisticated
tools made it easier to pinpoint the exact characteristics of chemical
compounds in air. The scientists used a 26-foot-long “aerosol flow tube”
at the AirUCI unit and a one-of-a-kind, 900-pound instrument known as
SPLAT (a single particle laser ablation time-of-flight mass
spectrometer) at the Pacific Northwest National Laboratory.
Co-authors
are Emily Bruns, Wayne Chang, Donald Dabdub, Michael Ezell, Stanley
Johnson and Yong Yu of UCI; M. Lizabeth Alexander and Alla Zelenyuk of
PNNL; Dan Imre of Imre Consulting; and James F. Pankow of Portland State
University. Funding was provided by the U.S. Department of Energy and
the National Science Foundation.
Nonequilibrium atmospheric secondary organic aerosol formation and growth
