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Sulfate Aerosol Evolution |
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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.
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