Washington, April 20 : In a new research, scientists have suggested that lead generated by human activities causes clouds to form at warmer temperatures and with less water, which could alter the pattern of both rain and snow in a warmer world.

The research has been done by an international team of scientists, which included researchers from institutions in the United States, Switzerland and Germany.

This is for the fist time that scientists have shown a direct relation between lead in the sky and the formation of ice crystals that foster clouds.

Atmospheric lead primarily comes from human sources such as coal.

"We know that the vast majority of lead in the atmosphere comes from man-made sources," said atmospheric chemist Dan Cziczo of the Department of Energy''s Pacific Northwest National Laboratory and study author.

"And now we show that the lead is changing the properties of clouds and therefore the balance of the sun''s energy that affects our atmosphere," he added.

Scientists first attempted to goad rain from the sky with silver and lead iodide in the 1940s. Since then, researchers have known that lead can pump up the ice crystals in clouds. B

ut daily human activities also add lead to the atmosphere.

The top sources include coal burning, small airplanes flying at the altitude where clouds form, and construction or wind freeing lead from the ground.

Cziczo and colleagues wanted to know how lead from these sources affects clouds.

To find out, the researchers collected air from high atop a mountain peak on the Colorado-Wyoming border.

In their high altitude lab, they created artificial clouds from the air in a cloud chamber about the size of a small refrigerator.

Half of the ice crystals they plucked from the synthetic clouds, they found, contained lead.

The team then collected a dollop of real cloud atop a mountain in Switzerland. About half of those ice crystals also contained lead.

To determine whether lead causes ice crystals and clouds to form, the team turned to a lab in Germany that houses a cloud chamber three stories tall, as well as a smaller chamber in Switzerland.

They created dust particles that were either lead-free or contained one percent lead by weight.

They put these dust particles into the chambers and measured the temperature and humidity at which point ice nucleated around the dust.

They found that lead changed the conditions under which clouds appeared.

"Most of what nucleates clouds are dust particles. Half of the ones we looked at had lead supercharging them," said Cziczo. (ANI)