Factory aerosols can transform the upper clouds
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Pollution plumes from large factories can cause snowfall and leave holes in clouds that spread over large areas, satellite images have revealed.
This has been known for a long time small particles of pollutants, such as sootknown as aerosol pollution, can They affect clouds in many ways. Water vapor can condense into pollutant particles, causing clouds to form, and so can pollutants changing the properties of existing clouds.
While examining these effects, Velle Toll At the University of Tartu in Estonia, they noticed that there were sometimes holes in the clouds from the wind of the main sources of pollution. He and his colleagues have now analyzed thousands of satellite images of North America and Eurasia and found 67 places where this effect can be seen under the right atmospheric conditions.
Weather radar confirmed that these events were causing snow. In the largest case the team found, 15 millimeters of snow fell over an area of 2,200 square kilometers (850 square miles).
This happens because the pollutant particles cause supercooled water droplets in clouds to freeze around them, creating ice crystals that grow on snowflakes, Toll says. “And if water comes out of the cloud as snow, we’ll end up with fewer clouds.”
In the absence of particles, water droplets in clouds can remain liquid even when the air is as cold as -40 °C (-40 °F).
This satellite image shows reduced cloud cover downwind of a Canadian copper smelter
Velle Toll
The 67 sources of pollution found by the team are mainly oil refineries and plants producing metals, cement or fertilizers. But surprisingly, the researchers occasionally observed a similar effect near four nuclear power plants that do not produce aerosol emissions.
This may be because warm air rising from these power plants lifts aerosol pollution from elsewhere, but the team has not confirmed this. “We don’t have a concrete explanation for that,” Toll says.
In theory, the aerosol effect could be used to cause snow on purposebut it would only work where there are already clouds of supercooled liquid water droplets, Toll says.
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