Radioactivity in the atmosphere over Hong Kong

Upper-air radioactivity soundings have been regularly conducted in Hong Kong since 1994. A total of 38 soundings, measuring the vertical profile of radioactivity in the atmosphere over Hong Kong using on-board Geiger-Müeller tubes, were made during the period 1994-2003 in different seasons and weather conditions. This paper presents the data obtained in Hong Kong and compares the composite vertical profile with observations in other parts of the world. The average Pfotzer maximum over Hong Kong was found to be at an altitude of around 16.1 km, lower than those observed at higher latitudes. The variations of the Pfotzer maximum with geomagnetic rigidity and solar activity are discussed. Seasonal and local weather effects on radioactivity in the lower atmosphere were also studied.