Models and Measurements

Models can help the researcher determine the UV/pollutant relationships, or the optical properties and physical characteristics of the pollutants utilizing data from numerous sources. Chemical and physical properties can now be retrieved with regional studies utilizing the newer instrumentation that allows specific ions to be collected and sized. In either case, one must always be aware of the quality of the data that is to be used and must investigate it fully to understand if it will meet the objectives for the accuracy and precision that are being sought. Models are excellent tools for the researcher through which atmospheric optical properties can be determined, but must be tested with real data to insure validity.

Below are two examples of such studies: (1) a statistical study from EPA data banks and a special study carried out by the California Air Resources Board were done to research the pollutant/UV interaction, and (2) an optical properties determination study in which the researchers took their own data from two sites in the mountains of North Carolina. In the second study, the optical properties of various aerosols were researched using models and doing reiterative processes to have the model output coincide with the measured values. Optical properties, such as asymmetry parameter or single scatter albedo, or measured particle sizes and aerosol chemical characteristics, can be determined in this manner. Keep in mind that aerosols are the major contributor to UV absorption in the troposphere and specifically the boundary layer, and ozone is the major absorber of UV in the stratosphere. Additionally, be aware that these studies were done on cloudless days. As mentioned earlier, clouds are major UV absorbers, but their chemical and physical properties and depths are generally not well known.

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