This paper discusses the design philosophy of the air quality surveillance systems which Kennecott is installing in the vicinity of its copper smelters in Arizona, Nevada, New Mexico, and Utah. These monitoring systems are part of supplementary control systems (SCS) that are utilized to ensure that short-term ambient air quality standards are met. These systems utilize minicomputers as remote terminals. The interface between a terminal and the primary sensors is via specially designed input/output circuitry. The system is controlled by a centralized host minicomputer, which is connected to each of the remote stations via a telephone line communication network. Real time data is displayed on cathode ray tubes located at strategic locations in the plants. This paper will discuss the system design philosophy from both a hardware and software point of view. The actual experience in design, development, and installation of the system will also be discussed.