Scientists have linked air pollution from multiple industries to the ocean’s increased potential to trap carbon.

An international team led by scientists at the University of Birmingham in the U.K. and Shandong University in China, have discovered that iron-rich particles likely from steel manufacturing and coal burning were prevalent in the East China Sea. These particles were found to have a thick sulfate coating containing soluble iron, providing evidence to show acid iron dissolution.

“Air pollution dissolves iron in aerosols, which may help to fertilize the oceans,” Zongbo Shi, Ph.D., a corresponding author of the study, said in a statement. “We know that air pollution seriously damages human health and terrestrial ecosystems but this ‘new’ source of soluble iron can potentially increase the amount of carbon dioxide stored in the oceans and thus, inadvertently offset global warming.”

Scientists have long believed that acids formed from human-generated pollution and natural emissions dissolve iron in airborne particles, which increases the amount of iron in the ocean, but they have lacked the direct evidence needed to prove the theory.

Weijun Li, the lead author of the study and a professor at Shandong University, explained the conclusion reached in the study.

“The detection of iron sulfate mixed within the sulfate coatings which we analyzed provides the ‘smoking gun’ for acid dissolution because there is no other atmospheric source or process that leads to its formation,” Li said in a statement.

The scientists collected three types of iron-bearing particles from the Yellow Sea—the northern part of the East China Sea located between mainland China and the Korean Peninsula. They used microscopic instruments to look for iron-containing nanoscale particles, specifically locating them from thousands of aerosol particles.

This showed that iron-rich, fly ash and mineral dust particles had travelled from Asia. The majority of the iron-rich and fly ash particles contained a significant amount of sulfate containing soluble iron.

Most atmospheric sulfur dioxide in East Asia is emitted from coal combustion and industry, while the bulk of sulfate particles in the Northern Hemisphere are formed from sulfur dioxide caused by human activities.

The research team confirmed that the iron rich sulfate particles found in the Yellow Sea are formed by contact with man-made sulfur dioxide. The new research shows that the airborne particles became acidic after being transported to the Yellow Sea.

“Human activities may have led to an increase of atmospherically soluble iron in the oceans by several times since the Industrial Revolution, which could have a major impact on how effective our oceans are regulating our climate,” Shi said. “Controlling air pollution will bring huge benefits to human welfare but it may reduce the amount of nutrients to the surface ocean and thus, the ocean carbon uptake rate.

“More work needs to be done to quantify the impact of anthropogenic soluble iron on ocean ecosystems and climate,” he added.