Research published Thursday in the Journal Science finds that data recorded during the massive oil spill last year in the Gulf of Mexico may add to the understanding of pollution in American cities.
Nearly a year ago the world watched as almost 5 million barrels of oil spewed into the Gulf of Mexico after the explosion of the Deepwater Horizon oil rig. The enormous oil slick was dotted with fires or controlled burns aimed at removing oil from the open water. Air quality was a concern and the National Oceanic and Atmospheric Administration sent in a specially-equipped Hurricane Hunter aircraft to access the situation.
The Lockheed Orion assigned to the mission had air quality and climate data instruments aboard that NOAA atmospheric scientist Joost de Gouw mined for data. "They give a very detailed analysis of the chemical composition of the atmosphere," he says.
On the first day of the mission, the aircraft made several wide loops over the oil spill site to measure its extent. De Gouw was part of the ground team and watched remotely via satellite, in real time: "And on every loop when we were downwind from the site we saw these very, very large signals of oil vapors, but we only saw it downwind from the spill site."
A front view of the Lockheed Orion WP3D aircraft loaded with sophisticated chemistry instruments.
The scientists calculated that about half the oil that surfaced was evaporating within hours or days, says De Gouw. "And what we saw was a very significant formation of organic aerosol from these vapors."
Organic aerosols are microscopic particles that remain suspended in the atmosphere and cause air pollution. Aerosols have been linked to asthma, heart disease and premature death. They also affect climate by reflecting more sunlight back into space. De Gouw says the mission to analyze Gulf air quality looked a lot like home. "In our cities about half of the aerosol is organic. And we also know that that organic fraction is not directly emitted from our vehicles, but it is formed in the atmosphere from organic vapors, we just don’t know which organic vapors are responsible for that very well."
Scientists measured aerosols over a broad area and concluded that the heavier, less volatile hydrocarbons in the Gulf of Mexico that didn’t evaporate so quickly might also be an important source of the organic aerosols turning up in the air in American cities and elsewhere. "And what was unique about our oil spill measurements," De Gouw says, "is we could study the chemistry of those compounds separately, because they were all separated on the surface of the Gulf as they evaporated on different time scales."
De Gouw says these heavier compounds are not usually measured in conventional air quality monitoring programs, which are designed to capture other contaminants like carbon monoxide, nitrogen dioxide, sulfur dioxide and ozone. The study, reported in the Journal Science, may also shed light on why there are more organic aerosols in polluted air than scientists can explain.