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Direct-sun UVB, total column ozone and water vapor, and aerosol optical thickness have been measured since 1990 at Geronimo Creek Observatory in South-Central Texas (29.6N 97.9W). Full sky and diffuse solar irradiance at UVB, visible and near-infrared wavelengths have been measured since 1994. Comparisons of total ozone measurements made from the surface by TOPS and MICROTOPS and from space by the Total Ozone Mapping Spectrometer (TOMS) show excellent agreement. Comparisons of UVB at solar noon measured at the surface by inexpensive UVB radiometers and inferred from TOMS ozone measurements give excellent agreement on days free of clouds. Scattering from the sides of clouds on summer days can cause UVB at the surface to exceed by 10-20% the UVB inferred from TOMS ozone measurements. Public service announcements of predicted peak UVB should include a correction factor for summer days when clouds are expected to be near the sun. Ultraviolet measurements at Geronimo Creek Observatory support various educational and biological studies, including development of inexpensive instruments, avoidance of UV by mosquito larvae (Culex pipiens), preferential selection by female C. pipiens of nursery pools with low levels of ambient UV, suppression of non-pigmented bacteria suspended in air and E. coli in water, and studies of sub-canopy and open-field growth of sapling trees.
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