The influence of water vapor absorption in the 290-350 nm region on solar radiance: Laboratory studies and model simulation

Water vapor is an important greenhouse gas in the Earth's atmosphere. Absorption of solar radiation by water vapor in the near‐UV region may partially account for up to 30% discrepancy between the modeled and the observed solar energy absorbed by the atmosphere. But the magnitude of water vapor absorption in the near‐UV region at wavelengths shorter than 384 nm is not known. We have determined absorption cross sections of water vapor at 5 nm intervals in the 290–350 nm region, by using cavity ring‐down spectroscopy. Water vapor cross‐section values range from 2.94 × 10−24 to 2.13 × 10−25 cm2/molecule in the wavelength region studied. The effect of the water vapor absorption in the 290–350 nm region on the modeled radiation flux at the ground level has been evaluated using radiative transfer model. Key Points Water vapor near‐UV absorption can affect solar flux at the ground