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Pollution Speeds up Snow Melt in Europe, Asia

the annual mean aerosol optical depth for 2006.

Aerosols are tiny particles, such as soot or dust, suspended in the Earth's atmosphere. In addition to their air-quality impacts, aerosols can interfere with sunlight reaching the planet's surface. Scientists often talk about aerosols in terms of their optical depth, which indicates how much incoming sunlight aerosols prevent from reaching the Earth's surface. The Moderate Resolution Imaging Spectroradiometer (MODIS) flying on NASA's Terra and Aqua satellites can detect aerosols. This image shows the annual mean aerosol optical depth for 2006, based on daily measurements made by MODIS. White represents little or no aerosol interference with sunlight, and dark orange indicates considerable interference. Areas where data could not be collected appear in gray.

Credit: NASA image by Reto Stockli, Earth Observatory; image interpretation by Lorraine Remer


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Photo showing industrial pollution.

Primary sources of industrial pollution include emissions from power plants, smelters and refineries, which pour oxides of sulfur and nitrogen, and other gasses, into the atmosphere. There, the oxides and gasses react with moist air to become sulfuric and nitric acids, resulting in the formation of acid rain. In addition, in the presence of sunlight, nitrogen dioxide reacts with hydrocarbons (mostly gasoline vapors that escape burning in automobile engines) and other gases to form ozone, the primary ingredient of the photochemical fog that covers many large cities. Scientists at the National Center for Atmospheric Research are tracing the complex chain of events linking emissions and airborne pollutants.

Credit: © University Corporation for Atmospheric Research


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Photo showing branches of lodgepole pine weighed down by a heavy snowfall.

A heavy snowfall weighs down the branches of a lodgepole pine in the Rocky Mountains of Colorado.

Credit: © University Corporation for Atmospheric Research


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the March-May impacts of black carbon, mineral dust and both agents on snow cover.

Modeling experiments show March-May impacts of black carbon (top), mineral dust (middle)and both agents (bottom) on snow cover in the Northern Hemisphere, averaged over the 1979-2000 period. From Flanner et al. (2009), Atmos. Chem. Phys.

Credit: © Mark Flanner


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