Air pollution from Asia, India and Indonesia is transported into the global stratosphere by the summer monsoon season, a study using a Canadian satellite has found.

This map shows concentration of hydrogen cyanide (red is highest, blue is lowest) at an altitude of 16.5 kilometres, measured by the SCISAT-1 satellite during the summer from 2004 to 2009. Arrows show horizontal winds at this level and the circulation associated with the Asian monsoon. ((Science/AAAS))

Researchers tracked the movement of hydrogen cyanide in the atmosphere using satellites and found the monsoon is an effective way for pollution from Asia to circulate around the world.

Hydrogen cyanide is a pollutant produced in the burning of biofuels and biomass, such as trees and grass. It's often used to track pollution from wildfires.

The chemical was chosen to determine the role of monsoons in spreading pollution because it remains in the atmosphere for up to four years, but breaks up in chemical reactions over the ocean.

The researchers measured levels and movement of hydrogen cyanide used infrared spectrometers on satellites like SCISAT-1, a Canadian satellite designed to make observations of the atmosphere.

The team used the satellite readings and computer models to show how the Asian monsoon pulls air upward from the Earth's surface deep into the stratosphere, the layer of the atmosphere that begins 10 kilometres above the surface.

Once the pollution reaches that level, it can remain in the atmosphere for several years. Some of the pollutants descend into the lower atmosphere while others break up in chemical reactions or in reactions with sunlight.

"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," said William Randel of the National Center for Atmospheric Research.

Randel is the lead author of the study published this week in the journal Science Express.

The researchers also said climate change could alter the effect of the Asian monsoon, although it's not clear when it would strengthen or weaken its pull of pollutants into the stratosphere.

The research was funded by the U.S. National Science Foundation, NASA and the Canadian Space Agency. Scientists at the universities of Toronto and Waterloo took part in the research, as well as researchers in the U.K.