Cloud view clears up

November 18, 2010

By: Smriti Sharma

Origin of aerosols dictates cloud shape

How cloudy is it outside? The answers may depend on the level of atmospheric pollution in one’s region. Cloud-forming microscopic particles, called aerosols, absorb and reflect solar radiation. These particles have the ability to modify cloud formation and encourage or suppress precipitation. They can be released from manmade sources like vehicles, industry, agriculture, and natural sources like sea salt, volcanic dust, sulphates from biogenic gases.

Scientists are not fully aware of the role of aerosols in affecting climate because of lack of information on their distribution and characteristics. Two scientific papers, published in the September 17 issue of Science, fill this gap.

In the first study more than 1,000 atmospheric aerosol profiles over the Pacific Ocean were analyzed. Their results demonstrated that aerosol concentration is higher in areas of human perturbation as compared to pristine regions. The study concluded that human intervention leads to aerosols with enhanced light scattering properties and radioactive effects, and increase in the number of particles available to form cloud droplets.

In the second study aerosol and cloud formation over the Amazon rainforests were studied during the wet season, when the air is at its most pristine. It was found that the forest produced its own rain, that is, clouds and rain were formed by volatile gases emitted by plants. The data also showed that the number of cloud droplets above the Amazonian forests depended directly on the number of aerosols. This is in contrast to more polluted areas, where the number of cloud droplets depends on how quickly hot particles from burning fires or fossil fuels ascend into the atmosphere.