3.1 Release of Tropospheric Ultraviolet-Visible (TUV) model version 5.3

The Tropospheric Ultraviolet-Visible (TUV) model continues to be used widely by the scientific community for applications including atmospheric photochemistry, solar radiometry, and environmental photobiology. The model calculates spectral radiance, irradiance, and actinic flux over 120-750 nm at an underlying resolution of 0.01 nm, as well as weighted spectral integrals including wavelength bands (visible, UVA, UVB, UVC), photolysis coefficients (112 reactions), and biologically active irradiances (UV index, DNA damage, vitamin D production, etc.).  Atmospheric inputs include vertical profiles of N2, O2, O3, NO2, SO2, clouds, and aerosols. The propagation of radiation through multiple atmospheric layers (concentric spherical shells for direct solar beam, plane-parallel for diffuse radiation) is computed using a fast 2-stream approximation or a multi-stream discrete ordinates scheme. Version 5.3 provides updated spectroscopic data for a number of photolysis reactions.

The propagation of radiation in surface waters (rivers, lakes, oceans) can now be calculated with TUV. The model uses simple refraction and absorption optics, including Snell’s law at the air-water interface, Fresnel reflection, and Beer-Lambert attenuation under-water for direct and diffuse light (but no underwater scattering).  Biologically significant UV exposures, e.g. DNA-damaging radiation, can be calculated as a function of depth, and used to estimate the effectiveness of solar disinfection within surface waters. This is illustrated in Figure 1 for Lake Giles (Pennsylvania) based on water absorbance measured recently compared to over 20 years ago.  This lake has experienced a marked increase in turbidity due to increased agricultural runoff, and illustrates the extent of change that might be expected in lake environments, in the face of climate change.

Sample template image
Figure 1:  Penetration of DNA-damaging radiation into the waters of Lake Giles (Pennsylvania), calculated with the TUV (v.5.3) model, based on spectral absorbance of water sampled in 1994 (blue) and 2015 (red).  Deviations from Beer-Lambert behavior are due to integration over multiple wavelengths.