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America pollution cloud on India

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By G.S. MUDUR
  • Published 21.01.10
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New Delhi, Jan. 20: Air pollution from eastern and southern Asia, possibly from China and India, may be causing spikes in atmospheric ozone levels over North America, a study has suggested.

The study by a team of international scientists has shown for the first time that tropospheric ozone, 3km to 8km above the ground, has been increasing during springtime over western North America from 1995-2008.

“The rate of increase is greatest when the air is transported directly from South and East Asia to western North America,” said Owen Cooper, a senior scientist with the US National Oceanic and Atmospheric Administration at the University of Colorado, and lead author of the study to appear tomorrow in the journal Nature.

While ozone higher in the stratosphere forms a protective blanket against harmful ultraviolet radiation from the Sun, tropospheric ozone lower in the atmosphere is a pollutant that can harm human health and crops.

The study suggests that America’s air quality could thus depend on pollution in Asia. However, an Indian researcher has pointed out that the study does not conclusively demonstrate an Asia link to ozone levels in North America.

Air pollutants such as oxides of nitrogen and volatile organic compounds released from fossil fuel-burning react with sunlight to produce ozone. The study has pointed out that the emissions of oxides of nitrogen from south and east Asia have increased 44 per cent during 2001-2006. But emissions of such ozone-forming chemicals have decreased both in the US and in Europe.

“Our findings indicate south and east Asia are associated with strongest ozone trends over western North America, but it cannot quantify the contribution from individual (Asian) nations,” Cooper told The Telegraph in an interview.

But a leading Indian scientist who specialises in the long-distance transport of air pollutants has said the new study is based on an interpretation of observations of ozone increases and does not establish Asia as its source.

“This does not provide any concrete evidence to show that the increase in ozone is because of pollutants from Asia,” said Gufran Beig, a senior scientist at the Indian Institute of Tropical Meteorology, Pune.

“The transport of ozone or ozone-forming pollutants from Asia to North America would have to be clearly demonstrated through pathways and timelines,” Beig told The Telegraph.

Some ozone-forming pollutants have too short a lifetime to survive a journey across the Pacific Ocean. The chemicals degrade and cannot form ozone any more, Beig said. The oxides of nitrogen, for example, have lifetimes of only hours or days, he said.

Cooper and his colleagues from Canada, France, and Norway had analysed some 100,000 ozone level measurements from separate studies by instruments aboard aircraft, balloons and other platforms.

The study, which shows a 14 per cent increase in springtime ozone in western North America from 1995 to 2008, was not designed to quantify the contributions from Asia. Cooper said contributions from specific regions would be a topic of future research.