Monsoon spreads pollution right through the stratosphere

Posted by Emma Woollacott

The Asian monsoon is sending pollutants up to stratospheric heights and spreading them right across the globe, says the National Center for Atmospheric Research (NCAR).

Using satellite observations and computer models, the research team found that the Asian monsoon rapidly transports air to a height of 25 miles - along with black carbon, sulfur dioxide, nitrogen oxides, and other pollutants.

"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," says NCAR scientist William Randel, the lead author. "As a result, the monsoon provides a pathway for transporting pollutants up to the stratosphere."

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.

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.

To isolate the role of the monsoon on the stratosphere, the researchers focused on hydrogen cyanide, produced largely by burning trees and other vegetation.

Satellite measurements showed significant amounts of hydrogen cyanide throughout the lower atmosphere and up into the stratosphere over the monsoon region. Furthermore, satellite records from 2004 to 2009 showed an increase 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.

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

The study will appear in Science Express.