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Study Finds Asian Monsoon Carries Pollution Into the Stratosphere

Time average mixing ratio (ppbv) of hydrogen cyanide (HCN) near 13.5 km during boreal summer (June- August) derived from satellite instrument observations. Arrows denote winds at this level derived from meteorological analysis, showing that the HCN maximum is linked with the upper tropospheric Asian monsoon anticyclone. Source: Randel et al., Science. Click to enlarge.

The Asian monsoon circulation provides an effective pathway for pollution from Asia, India, and Indonesia to enter the global stratosphere, according to a new international study led by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. The finding, published online 25 March in the journal Science, provides additional evidence of the global nature of air pollution and its effects far above Earth’s surface.

Using satellite observations (from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer, ACE-FTS) and computer models, the research team determined that vigorous summertime circulation patterns associated with the Asian monsoon rapidly transport air upward from the Earth’s surface. Those vertical movements provide a pathway for black carbon, sulfur dioxide, nitrogen oxides, and other pollutants to ascend into the stratosphere, about 20-25 miles above the Earth’s surface.

The monsoon is one of the most powerful atmospheric circulation systems on the planet and it happens to form right over a heavily polluted region. As a result, the monsoon provides a pathway for transporting pollutants up to the stratosphere.

—NCAR scientist William Randel, the lead author

Once in the stratosphere, the pollutants circulate around the globe for several years. Some eventually descend back into the lower atmosphere, while others break apart.

Scientists have long known that air over the tropics moves upward between the lower atmosphere and the stratosphere, part of a large-scale pattern known as the Brewer-Dobson circulation. But Randel and his colleagues suspected that the monsoon might also transport air into the stratosphere during the Northern Hemisphere’s summer months. This could explain satellite measurements showing high levels of stratospheric ozone, water vapor and other chemicals over Asia during summer.

To isolate the role of the monsoon on the stratosphere, the researchers focused on a chemical, hydrogen cyanide, which is produced primarily as a result of biomass and biofuel burning, and is often used as a tracer of pollution originating from fires.

The parcels of air over the tropical ocean that are lifted to the stratosphere by the Brewer-Dobson circulation contain low amounts of hydrogen cyanide, which breaks up over the ocean. But air over land that gets lifted up by the monsoon contains high levels of the chemical, especially during times of year when Asia has widespread fires, many set to clear land for agriculture.

When the scientists examined satellite measurements, they detected significant amounts of hydrogen cyanide throughout the lower atmosphere and up into the stratosphere over the monsoon region. Satellite records from 2004 to 2009 showed a pattern of increases in the chemical’s presence in the stratosphere each summer, correlating with the timing of the monsoon.

The observations also showed hydrogen cyanide, which can last in the atmosphere for several years before breaking up, moving over the tropics with other pollutants and then circulating globally.

The researchers used computer modeling to simulate the movement of hydrogen cyanide and pollutants from other sources, including industrial activity. The model indicated that emissions of pollutants over a broad region of Asia, from India to China and Indonesia, were becoming entrained in the monsoon circulation and transported into the lower stratosphere.

The study suggests that the impact of Asian pollutants on the stratosphere may increase in coming decades because of the growing industrial activity in China and other rapidly developing nations.

In addition, climate change could alter the Asian monsoon, although it remains uncertain whether the result would be to strengthen or weaken vertical movements of air that transport pollutants into the stratosphere.

Randel says more research is needed into the possible effects of the pollutants. When sulfur rises into the stratosphere, it can lead to the creation of small particles called aerosols that are known to influence the ozone layer.

The monsoon transport pathway may also have effects on other gases in the stratosphere, such as water vapor, that affect global climate by influencing the amount of solar heat that reaches Earth.

This is a vivid example of pollutants altering our atmosphere in subtle and far-reaching ways.

—William Randel

In addition to the NCAR researchers, the team included scientists from the Universities of Waterloo and Toronto in Canada, the University of York in England, and the University of Edinburgh in Scotland. The research was funded by the National Science Foundation (NSF), NCAR’s sponsor, along with NASA and the Canadian Space Agency.


  • William J. Randel, Mijeong Park, Louisa Emmons, Doug Kinnison, Peter Bernath, Kaley A. Walker, Chris Boone, Hugh Pumphrey (2010) Asian Monsoon Transport of Pollution to the Stratosphere. Science doi: 10.1126/science.1182274



Air pollution travels far and wide as expected.

Steve Funk

Anybody know whether they are tracking aluminum from this monsoon source. One of the popular conspiracy theories in my region is that the US military is already engaging in geoengineering, and local people are testing for aluminum and other elements. I suspect there are many possible sources for aluminum in water.


Steve, many silicate minerals [common to soil types around the world] contain aluminum. All you need to get aluminum in your water is acid rain.


"The study suggests that the impact of Asian pollutants on the stratosphere may increase in coming decades because of the growing industrial activity in China and other rapidly developing nations."

This is a prime reason why $$billions wasted on climate should be directed toward REAL pollutants coming from emerging industrials. Failure to act on these issues now WILL damage the eco-system and cause future human health failures. China needs a Clean Air Act with teeth.


China's per capita pollution level is still many times below Canada-USA-Australia and many other industrial nations.

When pollution created to produce all the exported manufactured goods, China's pollution level looks even better.

We may be barking up to wrong tree without looking closely enough to our own air pollution contribution.


Want help China stop polluting? Stop shopping at WalMart.


Harvey, China has already surpassed total US carbon emissions.  At its growth rates of recent history, how long will it be until its per-capita rate is also higher?

We need action now.  Tariffs on Chinese goods to hit the currency manipulation of the Yuan is a start.


I'm against the idea of tariffs as a general rule; I say "general" because I can see the need if nothing else works. Tariffs are anti-free trade protectionism that end up hurting the importer as much as the exporter. A better way is to level the playing field through regulated standards thet everyone must need: If China is unable to need those standards... well so be it.

Ideally you'd want to do this with a minimum of government bureaucracy. It would be good if this could be done through pre-existing structures - even better if you can off load the job to a third party.

My idea is to make all Green Seal- -labeled products/services sales tax free. It's simple and it puts the work and cost onto the company[which can choose whether or not to enter into the certification process] while giving the consumer a tax break for buying green goods.



It is very normal that China's total pollution is going up faster than USA. Look at their much faster growth in manufactured goods production and total population. China has become the world's factory for many common goods. To be fair, one would have to include imports/exports to arrive at NET national pollution. If you do that, USA with its huge trade deficits would have a much higher total and per capita pollution level and China with its huge trade surpluses would have a much lower total and per capita pollution level.

The total NET per capita could be as high as 40 tonnes in USA and as low as 5 tonnes in China.


Taking ai's idea it might be interesting to see if Wal Mart would pilot this. i.e. selectively contract for certified items and advertise them as tax free. This worked to get New York city's retail stores rejuvenated with sales tax "holidays" once or twice a month.

Trouble is the cost of cleanup (real pollutants) will be added to goods and services obviating the tax savings. And there is the cost of little regulated carbon transport.

If however, cost of cleanup gets a write off AND tax credits for the manufacturer - they may be better motivated to meet a certificate standard. Overall it's a good idea from a market POV.

But for China's government to allow these real pollutants to be emitted with no attempt at regulation - is totally absurd. And destructive to human health far from the pollutant sites.

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