Asia in the grip of aerosol heat

HYDERABAD: A joint study by the Isro and Nasa shows high concentrations of aerosols in the upper reaches of the earth’s atmosphere, about 16.5-18.5 km from the earth’s surface. This finding is crucial for the climate of the Asian region, which may get much hotter as aerosols will trap heat from higher altitudes. Aerosols are small particles that are dispersed into the air by various human and natural activities such as vehicular emissions, crop burning, coal emissions, volcanic eruptions, wind-blown dust etc. 

Aerosols could be of various chemical compositions, each of which could change the way aerosols impact the climate. For example, an aerosol which has a carbon element will absorb the heat and trap it in the stratosphere, whereas a sulphate element in the aerosol will make the particle highly reflective and result in the sun’s rays bouncing back. 

A joint study by Isro and Nasa shows high concentrations of aerosols in the upper reaches of the earth’s atmosphere. The size of the aerosol layer seen by Isro and Nasa in the Upper Troposphere and Lower Stratosphere is 0.25 micron. These pollutants usually stay at lower levels but have been blown upwards to higher altitudes due to the circulatory pattern of the monsoon winds in the months of July and August across Northern India.

“The presence of aerosols at a higher altitude means the climate impact of the aerosol will be more,” says Professor S.K. Satheesh, Chair of the Divecha Centre for Climate Change in Bengaluru.  He adds that once aerosols reach the stratosphere, they could affect the ozone layer.  Aerosols from Northern India mostly consist of carbon soot, due to the rampant practice of crop burning, leading to heat trapping particles spreading further up.

“What this study is referring to is the presence of aerosols higher up than we usually expect to see them, and the idea is that this layer of aerosols could mess with a number of things, including stratospheric ozone and cloud formation. The research team’s hypothesis seems to be that presence of these aerosols at that height could cause reactions with the ozone, and impact the ozone layer,” said Ms Pallavi Pant, post-doctoral research scientist at the University of Massachusetts at Amherst.

These fine particles, that are many times thinner in diameter than a human hair, can penetrate into the respiratory tract and cause damage. Professor G. Bala from the Centre of Atmospheric and Oceanic Sciences, Indian Institute of Science, adds, “Any particle in the air is polluting, right from dust to sulphur based aerosol or carbon based aerosol, and their impact on our health is serious. So even if sulphur aerosols can cool the earth, they can be damaging to the respiratory health of people.”