Monsoons launch ozone-depleting substances into the stratosphere

In the East Asian skies, monsoon winds are not just reshaping weather but are also unexpectedly carrying large amounts of ozone-depleating substances into the stratosphere.

This discovery, as highlighted by the U.S. National Science Foundation (NFS) and NASA, challenges previous assumptions about the rate of ozone recovery.

Monsoons and ozone recovery

Monsoons were primarily associated with seasonal shifts in rainfall, influencing agriculture and impacting local communities.

However, recent research reveals a more complex role for monsoons. The intense winds associated with monsoons, especially in Asia, can act as conveyor belts for pollutants. These powerful upward air currents carry pollutants from the Earth’s surface to much higher altitudes.

Climate change is intensifying the East Asian Monsoon system. This means an even greater potential for transporting large amounts of harmful chemicals into the upper atmosphere.

When carried high into the atmosphere, particularly the stratosphere, pollutants can interact with and deplete the ozone layer. Scientists are increasingly concerned about the transport of pollutants that were previously deemed less harmful due to their shorter lifespan. The monsoon now acts as a shortcut for these chemicals to reach the ozone layer

Very short-lived pollutants

For many years, scientists identified chlorofluorocarbons (CFCs) as the major threat to the ozone layer. CFCs are incredibly long-lasting; they stay active in the atmosphere for decades or longer, causing continuous damage to the ozone.

The Montreal Protocol was an international agreement aimed at phasing out CFC production and consumption. The treaty has been remarkably successful and is a testament to how collective action can address environmental challenges.

Scientists are now worried about a new class of pollutants called “very short-lived” ozone-depleting substances (VSLS). These chemicals, used in various industries, were assumed to be less harmful because they degrade faster in the lower atmosphere.

Industrialization, particularly in South and East Asia, has led to a significant increase in VSLS emissions. This poses a new challenge for protecting the ozone layer.

Even though VSLS break down relatively quickly near the Earth’s surface, the question is: What happens if these chemicals get transported higher into the atmosphere? If they manage to hitch a ride directly to the stratosphere, where the ozone layer is, their shorter lifespan becomes irrelevant. The ozone-depleting potential of VSLS still poses a threat, even if for a briefer period.

Monsoons hamper ozone recovery

The NSF National Center for Atmospheric Research (NCAR) and NASA study, part of the Asian Summer Monsoon Chemistry and Climate Impact Project (ACCLIP), paints a worrying picture. Scientists made airborne observations of the monsoon system finding:

• Compared to the South Asian monsoon, the East Asian monsoon showed significantly higher levels of pollutants – a nasty cocktail including some surprisingly high concentrations of carbon monoxide.
• Worryingly, the scientists found large quantities of VSLS, such as dichloromethane and chloroform. These chemicals are increasing due to industrial activities, mainly in East China.

“It was a real surprise to fly through a plume with all those very short-lived ozone-depleting substances,” says NSF NCAR scientist Laura Pan, the lead author of the study. “These chemicals may have a significant impact on what will happen with the ozone layer, and it’s critical to quantify them.”

Escalator for harmful pollutants

The Montreal Protocol aimed to limit long-lived ozone-depleting substances to give the ozone layer a chance to heal. Yet, this monsoon-driven boost of VSLS could complicate that recovery.

This is a grim reminder that climate change isn’t just about rising temperatures. It also creates these unintended consequences, like strengthening the East Asian Monsoon, which acts as an escalator for harmful pollutants. Scientists will need to take these findings into account when modeling the ozone layer’s future and the impacts on our climate.

This research raises important questions about the combined impact of pollution, monsoon patterns, and climate change on the ozone layer. To get a complete picture, scientists need to track these VSLS more closely and figure out how they interact with the ozone layer at those altitudes.

“The potential impacts of the high levels of these chemicals will need to be taken into consideration for projections of both the recovery of stratospheric ozone as well as climate change,” explained Laura Pan.

The fight to protect our ozone layer continues. Just when we thought we were making progress, this study reminds us that in our interconnected world with changing climate patterns, new threats can always emerge.

The study is published in the journal Proceedings of the National Academy of Sciences.

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