The 2010 Deepwater Horizon (DWH) event released approximately 4.9 million barrels of crude oil over three months, making it the largest accidental marine oil spill in history and a declared Spill of National Significance. While the disaster is often associated with its devastating effects on the marine environment and Gulf Coast beaches, the event also created a massive, temporary atmospheric pollution event over the Gulf of Mexico. The atmospheric impacts resulted directly from the oil and gas release and the subsequent cleanup response. Studying the atmospheric plume provided scientists a rare opportunity to analyze how a massive, concentrated release of hydrocarbons interacts with the atmosphere.
Release of Volatile Organic Compounds and Methane
The crude oil released from the Macondo well contained numerous light components known as Volatile Organic Compounds (VOCs), including toxic chemicals like benzene, toluene, ethylbenzene, and xylenes (BTEX). These compounds readily evaporate from the massive oil slick, forming a significant plume of gaseous hydrocarbons that became the largest source of primary air emissions from the spill. Once in the atmosphere, these VOCs reacted with other airborne chemicals, generating a substantial amount of Secondary Organic Aerosol (SOA) particles. Scientific analysis determined that SOA formation resulted in a mass yield of about 8% of the total oil that evaporated from the sea surface.
The leak originated far below the surface, influencing the fate of the natural gas released with the oil. The wellhead released tremendous quantities of methane, a powerful greenhouse gas, directly into the deep water column. However, the vast majority of this methane did not survive the 5,000-foot journey to the ocean surface. The methane largely dissolved into the deep water column, where it was consumed by a rapid bloom of naturally occurring, methane-eating microbes. Scientific monitoring confirmed that no elevated levels of methane reached the atmosphere, preventing a major atmospheric release that would have had a significant climate impact.
Particulate Matter from Controlled Burns and Flaring
A secondary, highly visible atmospheric impact resulted from intentional cleanup efforts, primarily the use of controlled burns to reduce the surface oil slick. During the nine weeks of active burning, the incomplete combustion of crude oil released large amounts of solid particles directly into the air. These emissions formed massive, dark smoke plumes rich in black carbon, commonly known as soot.
These controlled burns pumped an estimated 1.4 million to 4.6 million pounds of black carbon pollution into the atmosphere. This quantity was roughly equivalent to the total black carbon emissions normally produced by all shipping traffic across the Gulf of Mexico over a similar nine-week period. Approximately 4% of the mass of the oil that was burned was released as black carbon aerosols.
The intense heat caused the soot plumes to rise much higher into the atmosphere than typical emissions. This lofting potentially prolonged the time the black carbon remained suspended, affecting how far the pollution traveled. Although these soot plumes were visually dramatic, the total mass of the invisible SOA particles formed from evaporating oil was ultimately about ten times greater than the mass of the black carbon released by the burns.
Local Air Quality and Human Exposure
The massive atmospheric plumes of VOCs and particulate matter created significant, temporary degradation of air quality near the spill and along the Gulf Coast. The total air pollution generated was comparable in scope to the emissions from a large metropolitan area, including elevated levels of primary emissions and secondary pollutants like ozone and fine particulate matter downwind.
Air monitoring data showed temporary spikes in pollutant concentrations in coastal areas. Onshore measurements indicated that benzene concentrations were temporarily 2 to 19 times higher, and fine particulate matter (PM2.5) was 10 to 45 times higher than pre-spill levels. These elevated concentrations occasionally exceeded public health criteria, raising concerns for coastal communities.
The human exposure risks were most pronounced for cleanup workers and residents living along the shoreline. Many people experienced acute symptoms such as headaches, nausea, and respiratory irritation from inhaling the hydrocarbon vapors and fine particles. While total exposure levels for workers were generally below occupational standards, the scale and duration of the event made air quality a serious, localized health concern.
Scientific Monitoring of Atmospheric Plumes
To accurately quantify the atmospheric impact, scientists rapidly deployed sophisticated measurement techniques during the spill response. Researchers from the National Oceanic and Atmospheric Administration (NOAA) utilized specialized aircraft, such as the WP-3D, equipped with advanced sensors. These aircraft flew directly through the plumes to measure the concentration of VOCs, methane, and various aerosol species in real-time.
Instruments like the single-particle soot photometer provided detailed information on the physical and chemical characteristics of the black carbon particles released by the controlled burns. The data collected from these airborne missions were crucial for distinguishing between the primary emissions from the evaporating oil and the secondary pollutants that formed downwind. Scientists also used this information in atmospheric modeling to estimate the total quantity of gases and particles released and to track the movement and eventual fate of the plumes.