WASHINGTON (Reuters) - The BP oil spill that sent 4 million barrels of crude into the Gulf of Mexico last year also created air pollution, and studying this pollution gave scientists clues into how these contaminants get into the atmosphere.
BP's Deepwater Horizon rig exploded on April 20, 2010, killing 11 people and spewing oil from the underwater well that rose to the surface. It also created a plume of air pollution downwind of the spill, researchers reported in the journal Science.
The lightest chemicals in the oil evaporated within hours, as scientists expected them to do. What they didn't expect was that heavier compounds -- the ones with more carbon atoms per molecule -- in the oil took longer to evaporate, spread out much more widely and contributed most to the formation of air pollution particles.
"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," Joost de Gouw, a scientist at the U.S. National Oceanic and Atmospheric Administration and a co-author of the study, said in a statement.
To measure the pollution above the Gulf, NOAA sent a "hurricane hunter" plane equipped to monitor air quality to make two flights over the area in June 2010, while oil was still spilling.
The plane, a Lockheed WP-3D Orion, was fully loaded with instruments designed to measure different types of air pollution particles, including organic aerosol and the chemicals from which they form.
AIR POLLUTION PARTICLES
But the plane did not measure the heavier compounds that ultimately contributed most to air pollution, because most air quality monitoring equipment is designed to look at the conventional contributors to poor air quality, which are the lighter, more volatile materials.
Aerosols are microscopic particles suspended in the air, the same size particles as in spray deodorant or hair spray. Organic aerosols come from organic material and are linked to asthma, cardiovascular disease and even premature death.
They make up about half the air pollution particles in polluted U.S. cities. But scientists have identified only a small fraction of the organic aerosols.
To figure out where all this organic aerosol came from, de Gouw and his colleagues ran computer models of how various weights of oil -- heavy, medium and light -- spread across the Gulf and how long it would take each to get into the atmosphere.
The heavier compounds were the clear culprit, the researchers found.
Air pollution particles also can affect climate, with some particles, including organic aerosol, counteracting greenhouse warming by reflecting sunlight. Other particles have the opposite effect, increasing warming by letting the atmosphere absorb more sunlight.
There was about the same amount of organic aerosol in the plume above the Gulf as there is in U.S. urban air.
"This chemistry could be a very important source of aerosol in the United States and elsewhere," de Gouw said. "What we learned from this study will actually help us to improve air quality understanding and prediction."
(Reporting by Deborah Zabarenko; Editing by Cynthia Osterman)