Radon is a dangerous radioactive gas that is always present in the environment. It is important that students and society in general are aware of radon as a health hazard. This study describes a simple experiment to measure the variations of radon gas concentration outdoors. We compared the concentration of radon gas in the environment in dry and wet weather conditions and at different times of day. The results show that outdoor radon concentrations are significantly lower, by as much as 50%, during cloudy and rainy conditions.