Environmental conditions for the roughly three million people living in the Taipei basin of Taiwan are greatly affected by the land-sea breeze and afternoon thunderstorm activities. A new perspective on the land-sea breeze life cycle and how it is affected by afternoon thunderstorm activity in the Taipei basin during the dry season is provided. During the summer monsoon break-revival phase, about 75% of rainfall in the Taipei basin is produced by afternoon thunderstorms triggered by sea-breeze interactions with the mountains to the south of this basin. Because the basic characteristics of the land-sea breeze and the changes it undergoes through the influence of afternoon thunderstorms have not been comprehensively analyzed/documented, a mini-field experiment was conducted during the summers of 2004 and 2005 to explore these aspects of the land-sea breeze in this basin. Thunderstorm rainfall is found to change not only the basin's land-sea-breeze life cycle, but also its ventilation mechanism. On the nonthunderstorm day, the sea breeze supplies the opensea fresh air for about 8 h during the daytime, but the land breeze persists on the thunderstorm day from afternoon to the next morning, acting to sweep polluted urban air out of the basin.