Sulfate Aerosol Evolution

The NCAR Community Climate Model (CCM3) is used to model sulfate aerosols in
the atmosphere that originate from coal burning and smelting operations around
the globe.Researchers at NCAR used the CCM3 model to show global sulfate
aerosol evolution and how sulfate aerosols are transported between different
continents. The sulfate aerosols shown here are primarily from man-made sources
including coal burning and copper smelting. Other natural sources (20% of the
total) such as dimethyl sulfide produced by phytoplankton in the ocean and
volcanic emissions are not modeled in this case study. Emissions are seasonal.
For example, in Europe, there tends to be more coal buring during the winter to
produce energy for heating. In the US, however, emissions are more constant.
Like Europe, coal is burned in the winter to produce power for heat, but
because of energy demands for air conditioning systems, which are more
prevalent in the US than in Europe, yearly sulfate emissions are more constant
in North America.

Seasonal variations, however, are dominated by the chemical process of
converting sulfides into sulfate aerosols. A process which requires sunlight
and water vapor. These elements are more prevalent in the North American
summer, and so we see peak levels in June, July, and August.
There are two main effects from the increased sulfate aerosol levels in the
atmosphere: the direct and indirect effects. The direct effect is that
radiation is scattered back into space resulting in less energy entering the
climate system. Some theories propose that this leads to a cooler climate and
helps mitigate global warming.

The indirect effect is that the sulfate aerosols act as cloud condensation
nuclei resulting in the formation of more drops compteting for the same amount
of water vapor. This produces clouds that persist longer and that have smaller
droplets that do not precipitate as easily, and they are brighter, reflecting
even more radiation. This, in turn, may offset the greenhouse effect.