Air Pollution From BP Oil Spill
Reaching Far Beyond The Gulf
March 15, 2011 - During a special airborne mission to study the air-quality impacts of the BP Deepwater Horizon oil spill last June, NOAA researchers discovered an important new mechanism by which air pollution particles form.
Although predicted four years ago, this discovery now confirms the importance of this pollution mechanism and could change the way urban air quality is understood and predicted.
The NOAA-led team showed that although the lightest compounds in the oil evaporated within hours, it was the heavier compounds, which took longer to evaporate, that contributed most to the formation of air pollution particles downwind.
Because those compounds are also emitted by vehicles and other combustion sources, the discovery is important for understanding air quality in general, not only near oil spills.
oil slick, seen from the window of the Lockheed WP-3D
Orion aircraft. Best known as one of NOAA's "hurricane
hunters," the plane was outfitted with chemistry
instruments for a mission in
?We were able to confirm a theory that a major portion of particulate air pollution is formed from chemicals that few are measuring, and which we once assumed were not abundant enough to cause harm,? said Joost de Gouw, lead author of a new paper on the finding, published in the March 11 edition of Science.
De Gouw is
an atmospheric scientist in the Chemical Sciences Division of
NOAA?s Earth System Research Laboratory in
a research aircraft to the Gulf region in June 2010 to help
other agencies assess pollutant levels in the air. The Lockheed
WP-3D Orion aircraft, best known as NOAA?s ?hurricane hunter,?
aerosol, or OA, makes up about half of the air pollution
particles in polluted
De Gouw said he and his colleagues knew where to expect OA particles downwind from the oil spill based on conventional understanding: OA should form when the most lightweight, or ?volatile,? components of surface oil evaporate, undergo chemical reactions, and condense onto existing airborne particles.
Twenty to 30
percent of the surface oil fell into this volatile category, evaporating
into the atmosphere within hours, according to the new analysis. That
gave it little time to spread out, so emissions came from the area
immediately surrounding the spill. A steady wind such as the one blowing
during a June 10, 2010 research flight drew those emissions into a thin,
linear streak of pollution in which organic aerosol was expected to
?But that?s not
what we saw,? de Gouw said. ?We saw this very broad plume of organic
aerosol instead.? OA levels in that plume were similar to levels found
So de Gouw and his
colleagues set about trying to figure out what else might have
contributed to the pollution particles. In 2007, other atmospheric
scientists had proposed that heavier or ?less volatile? components could
theoretically help to create OA, but it had proven to be near impossible
to study this process in the real world.?The problem is that the heavier
and lighter species are emitted at the same time from the same sources,
so we could not study them separately in the atmosphere until Deepwater
Horizon,? de Gouw said.
of oil take longer to evaporate, so they had more time to spread on the
surface farther from the spill source than their lightweight siblings.
When de Gouw and his colleagues ran a series of models showing how
spilled oil spread across the Gulf, and how long it should take for
various heavy, medium, and light fractions to evaporate, the conclusion
was clear. The heavier, less-volatile compounds from the oil that were
not actually measured by all the sophisticated instruments onboard the
aircraft were the culprit.
compounds are not measured in most air quality monitoring programs,
which were designed to capture the conventional contributors to poor air
quality. The new findings may also help understand why there is more
organic aerosol in the polluted atmosphere than scientists can explain.
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