Published: Sunday 30 November 2008

Aerosols above the Himalaya may alter regional thermostat

nano-sized pollutants were for the first time found reacting with each other above the Himalaya.

Scientists from the Universite Blaise Pascal, France, said these ultra-fine pollutants are combining to form aerosols -- tiny particles, solid or liquid, that remain suspended in the atmosphere. Though such consolidation of pollutants were observed previously in rural, marine and urban areas, their occurrence at such high altitudes was not documented before.

Aerosols absorb sunlight and contribute to atmospheric warming. Since the ultra-fine particles are giving rise to more aerosols, the scientists believed this could lead to a warmer upper Himalayan atmosphere, which in turn could trigger glaciers to melt and impact monsoons, said the scientists in the journal Proceedings of National Academy of Sciences (Vol 105, No 41).

They studied the 16-month record of aerosol distribution from the Nepal Climate Observatory at Pyramid (5,079 metre above the sea level), and inferred that aerosol concentrations in the atmosphere increased significantly when there was an increase in the concentration of ultra-fine pollutants in the upper Himalayan atmosphere. The record also showed that most of the new aerosols formed at noon in the post-monsoon seasons; up to 2,000 new aerosols ranging between 10 and 40 nanometres were formed per cubic centimetre area. The problem will worsen as the concentration of ultra-fine pollutants increase, the team said. Previous studies had also shown that aerosols from industrial pollution led to atmospheric warming.

Some scientists doubted this. Particles less than five microns in size did not contribute to atmospheric warming, they believed. Since the maximum size of the new aerosols was 40 nanometres, it was unlikely that they would have any influence on the atmosphere above the Himalaya or the monsoon cycle, they said.

Ultra-fine particles have long been linked to vehicular pollution but the team couldn't pinpoint the exact source. They claim the findings will help design future climate models.

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