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Aerosols - summary

Aerosols

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Aerosols - summary

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    1. Aerosols - summary They impact health, climate, weather. They come from mechanical (big ones) and chemical (little ones) processes. They leave the atmosphere by falling out (big ones) or being taken up into rainfall (little ones). They have a lifetime of about 1 week. Human activities have substantially increased the amount of aerosol in the earth’s atmosphere. They grow by condensation and coagulation. Beyond 1 mm in size, their number distribution roughly conserves volume.

    2. Aerosols – more summary There are lots of them in the troposphere (~10 to 103 cm-3) and they are typically small (< or = 1 mm). There are more over continents than over oceans. Fall velocities depend on size. They have to get pretty big to fall out of the air (~ 10 to 100 mm). A subset of aerosols serve as cloud condensation nuclei. The larger the number of CCN, the more and smaller the drops there are in a cloud.

    3. 0. What is an aerosol? The term “aerosol” in our case refers to a mixture of “particles” suspended in a gas (air). A cloud is an aerosol. Haze and smoke are aerosols. All air on the earth contains particles, hence has the properties of an aerosol. The particles are not always visible. The particles can be liquid or solid.

    4. 1. How are aerosols relevant to us? Aerosols can pose a serious respiratory hazard. In the U.S. small particulate concentrations are regulated by the EPA. Aerosols reduce visibility. In the US, federal law regulates visibility reduction in National Parks. Climate is influenced by aerosols. They scatter and absorb radiation (e.g. Pinatubo - Jacob Fig8.6, IPCC - overhead), generally cooling climate. They alter the sizes and number of cloud drop, changing cloud optics. They provide sites for atmospheric chemistry (e.g. Jacob C10, stratospheric ozone depletion, C8, acid rain). They are one of 3 elements required for cloud formation (other 2 are H2O and a cooling mechanism).

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