The wealth of air pollutants that were generated in the atmospheric plume as a result of the Deepwater Horizon oil spill in 2010 amounted to levels similar to the pollution created by a large city, says a new study led by researchers from the National Oceanic and Atmospheric Administration.
“The levels of ozone were similar to what occurs in large urban areas. During the oil spill, it was like having a large city’s worth of pollution appear out in the middle of the Gulf of Mexico,” said Daniel M. Murphy, NOAA scientist at ESRL/CSD and a co-author of the study.
Researchers from the NOAA Earth System Research Laboratory (ESRL) and NOAA’s Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colorado, along with university colleagues, focused on calculating the amounts of ozone and particulate matter, two pollutants which directly effect humans.
Their data was gathered during the aftermath of the oil spill in June 2010 on two flights of NOAA’s WP-3D research aircraft as well as data gathered on ships in the vicinity and at two monitoring sites in Mississippi, downwind of the oil spill.
They found that approximately eight percent – or about one of every 13 barrels of the Deepwater Horizon-spilled oil that reached the ocean surface – made its way into airborne organic particles that would be small enough for a human to inhale. According to the study, some of these particles likely reached the Gulf coast thanks to favourable (or unfavourable) winds.
“We could see the sooty black clouds from the burning oil, but there’s more to this than meets the eye. Our instruments detected a much more massive atmospheric plume of almost invisible small organic particles and pollutant gases downwind of the oil spill site,” said Ann M. Middlebrook, scientist at NOAA ESRL’s Chemical Sciences Division (CSD) and lead author of the study.
During an oil spill such as this, a controlled burn is often initiated in an attempt to reduce the size of the surface oil and minimize its impact on the surrounding ecosystems. According to the study, the total mass of organic particles that were formed from evaporating surface oil – when compared to the soot from the Deepwater Horizon controlled burns – was over ten times larger.
As a result of this evaporation an atmospheric plume was created as hydrocarbons were released and eventually grew to some 30 kilometres wide by the time it reached the coast.
Another plume was created when hydrocarbons from the evaporating oil reacted with nitrogen oxides in the atmosphere, creating ozone pollution, but this was a smaller plume hat only reached to 3 or 4 kilometres wide.
The authors note that their findings could help air quality managers anticipate the effects of future oil spills. The depth of the Deepwater Horizon spill, about a mile beneath the surface, limited the effects on air quality because some hydrocarbons, such as benzene, largely dissolved in the water.
“It was fortunate that the effects on air quality of the Deepwater Horizon oil spill were limited in scope,” said Middlebrook. “Our findings show that an oil spill closer to populated areas, or in shallower waters, could have a larger effect.”