What factors other than stratospheric ozone control UV-B radiation?
Significant additional absorption and scattering occurs by clouds, and by ground level pollutants such as sulfur dioxide, nitrogen dioxide, low-level ozone, and atmospheric aerosols. Clouds can reduce UV-B radiation at the surface by up to 90%, or even increase it by up to 20%. Furthermore, the large variability of clouds from year to year makes detection of long-term trends in UV-B difficult.
