New Delhi, March 25: Wind patterns during the monsoon waft air pollutants from India high into the atmosphere to pollute the stratosphere, scientists have said in a fresh study blaming Asia for distant air pollution.

An international research team has combined satellite observations and computer models to suggest that monsoon circulation serves as an effective pathway to carry pollution from India and other parts of South Asia into the stratosphere.

The findings may represent the first unambiguous observations that the monsoon winds transport pollutants into the stratosphere — the region of the atmosphere that begins about 20km above the Earth’s surface and holds the protective ozone layer.

“The (South Asian) monsoon is a pathway to the stratosphere during the Northern hemisphere summer,” said William Randel, a scientist at the US National Centre for Atmospheric Sciences, Boulder, Colorado, and the study’s lead author.

“The pathway also happens to sit directly on top of a polluted Asian region,” Randel said. The study will appear in the US journal Science tomorrow.

Randel and his collea- gues from Canada and the UK relied on satellite observations of hydrogen cyanide, a compound produced from biomass and biofuel burning, during the monsoon seasons between 2004 and 2009.

The changes in hydrogen cyanide in the stratosphere over the five years appear linked to the monsoon.

Computer simulations have also suggested that pollutants from India, China and Indonesia are likely to be carried into the stratosphere.

The researchers believe their findings may also apply to other pollutants such as sulphur dioxide and oxides of nitrogen.

However, an Indian scientist studying atmospheric pollutants has questioned the significance of the findings, saying that stratospheric pollution from Asia’s growing levels of pollution emissions would have hurt stratsopheric ozone.

“The oxides of nitrogen can contribute to ozone de pletion. Instead, the ozone hole in the high latitudes has been steadily recovering,” said Ghufran Beig, a senior scientist at the Indian Institute of Tropical Meteorology, Pune.

While hydrogen cyanide molecules have a lifetime of about four years, Beig said, the oxides of nitrogen have lifetimes of just a few months.

Two months ago, an independent team of international scientists had reported that air pollution from eastern and southern Asia, may be causing spikes in ozone levels over North America.

The study had suggested that America’s air quality may depend on Asia’s pollution.

Randel said more research would be needed to predict the possible impacts of the pollutants.

The chemicals transported through the monsoon (winds) may be relevant to ozone and the amount of solar heat that reaches the Earth.