We present here an analysis of the airborne radioactivity measured in Italy after the Chernobyl accident. We provide some quality assurance, isolate suspicious data, and devise a mathematical model to aid in interpreting time-dependent fallout data. The model consists of an interpolating function whose parameters can be related to 1) the arrival time of the radioactive cloud; 2) the time of the maximum radioactive concentration; and 3) the decay-rate of airborne radioactivity as the pollutant cloud passes. Multiple arrivals of the radioactive cloud in a given site can also be considered. The parametrization can be used to estimate concentrations of 137Cs using measurements of (131)I, 103Ru, or 132Te. The interpolating function is fitted to the data collected in several Italian Provinces. We feel this model is an useful tool for interpreting time-dependent fallout data.