Part of the Understanding Our Environment project that is designed to engage students in investigating specific environmental problems through concrete activities and direct experience, this unit uses the contemporary dilemma of acid rain as a vehicle for teaching weather and the characteristics of air and atmosphere. The project involves a hands-on activity in which students examine and compare mock rainwater samples from a fictional remote site in the United States. Information gathered and questions raised in the course of this activity are used to examine weather patterns and to discover how weather is a result of the atmosphere's structure and scale. As a follow-up, the global issues of stratospheric ozone depletion and greenhouse warming are introduced. The objectives include: learning about all aspects of the problem of acid precipitation; drawing inferences about how pollutants are transported through the atmosphere; appreciating the processes and characteristics of the atmosphere; understanding how weather is a function of atmospheric processes; investigating the role of airborne particles in cloud formation; and learning about smog, greenhouse warming, and ozone depletion. (JRH)