Observations of short-lived radon 22 daughter concentrations in surface air have been continuously carried out at a site near the Japan Sea coast for a period of about 1 year, together with measurements of solar and net radiation amounts. It is concluded from the analysis of these data that increases of solar radiation during the daytime and heat emission during the nighttime cause progressive decreases and increases of the radon daughter concentration, respectively. ¿ American Geophysical Union 1988