The amount of UV radiation reaching the earth's surface is affected by air pollution, i.e., absorption by aerosols (black carbon, dust, and smoke), tropospheric O3, NO2, and other gases. These can cause typical reductions in UV radiation by up to 15% in polluted sites, but with much higher reductions occurring in certain highly polluted cities, e.g., occasionally in Los Angeles and frequently in Beijing. NO2 causes small reductions, mainly to UV-A, since its absorption cross-section peaks near 410 nm, yet is still significant at 330 nm. Aerosols of most types affect UV and VIS radiation at all wavelengths. Pollution abatement, especially in highly polluted regions, can decrease the atmospheric reflectivity and absorption, which has the effect of increasing the amount of UV and VIS radiation reaching the ground. The reductions in surface UV can be much higher in regions affected by smoke (e.g., biomass burning) or by the major dust storms that frequently occur in Africa and parts of China.
Absorption of UV and VIS irradiance/radiance is used to determine the amount of pollution (O3, SO2, HCHO, NO2, H2O) in the atmosphere by matching the measured and calculated spectrum reaching ground-based spectrometers or reflected back to a satellite spectrometer (e.g., OMI and GOME) (Cede et al., 2006; Wenig et al., 2006).
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