美国英语听力80篇2 Lesson31
Rainfall Decreased
An Israeli study has shown that air pollution from cities and industry can reduce rain and snowfall.
It says the problem appears to be linked to the number of pollution particles in clouds.
Daniel Rosenfeld of Hebrew University in Jerusalem organized the study.
His findings were reported in the publication Science.
Mister Rosenfeld observed air pollution over Australia, Canada and Turkey from cities and factories.
He used images provided by a satellite orbiting Earth.
The satellite has instruments that can measure clouds and rainfall.
Raindrops form in clouds with little or no pollution when water in the air collects around dust particles.
The study notes that about 1,000,000 small droplets are required to form a drop of water large enough to fall to earth.
Mister Rosenfeld observed the movement of the air pollution as it floated away from cities,
power production centers and oil treatment centers.
He found that heavily polluted clouds do not produce as much rain as cleaner clouds.
He says this is because polluted clouds are made of only very small water droplets.
Mister Rosenfeld says polluted clouds have too many dust particles.
The large number of particles results in the formation of too many water droplets that are too small.
They are not big enough to form raindrops.
The smaller droplets also are slower to freeze and do not easily form ice particles for SHOW.
Last year, Mister Rosenfeld found that burning trees and other plants also reduces rainfall amounts.
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