Red Sea is potent source of hydrocarbon emissions

Intensive fossil fuel production in the Middle East is a major source of non-methane hydrocarbons (NMHCs) such as propane and ethane. These gases linger in the atmosphere and can interact with other emissions to produce smog and other harmful compounds.  “However, air chemistry measurements in this region are scarce,” notes Bourtsoukidis. To address this problem, his team embarked on the Air Quality and Climate Change in the Arabian Basin (AQABA) study in 2017. They transformed a research vessel into a seagoing laboratory, outfitted with a host of instruments for detecting NMHCs and other emissions.

Most of their findings mirrored initial predictions, with high NMHCs in areas of strong industrial activity. But there was one big surprise: a spike in NMHC emissions in the northern Red Sea. “We initially assumed that these high ethane and propane concentrations were due to sources located along the Suez Canal, such as fossil fuel exploitation, biomass burning, and marine traffic,” says Bourtsoukidis. But careful mathematical and statistical analysis showed this was not the case.

Instead, this surge in ethane and propane levels originates deep beneath the sea, arising from sources that include leaky underwater reservoirs of hydrocarbons as well as biological activity. “We spent almost two years working on this dataset to confidently prove that these emissions were coming from some two kilometres beneath the sea’s surface,” says Bourtsoukidis. These gases are subsequently relayed to the surface by undersea currents. 

In the past, such NMHC release would have a negligible impact on human health. But today, these gases interact with nitrogen oxide produced by ship traffic, which has been steadily increasing in the Red Sea. “This results in the production of ozone and peroxylacetyl nitrates, which are very harmful to human health,” says Bourtsoukidis. “This pollution is spreading to remote, unpolluted areas.” He and his team are continuing to work with the AQABA data to understand its environmental implications for the Arabian Peninsula, including the potentially strong contribution of deep-water sources to methane release.

Eric Apel of the US National Center for Atmospheric Research in Boulder, Colorado, who was not involved in the study, says "the authors did a good job of showing that the Red Sea is a large and unexpected source of methane and light hydrocarbons that can have some significant implications for air quality in the region, now and into the future".

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