We consider the design and operation of an absorption integrated optical chemical sensor, which provides control of the content of ammonia and other hazardous gaseous and liquid substances in the air. An integrated optical sensor based on a diffusion waveguide is studied. The advantage of measurement schemes in which an analog signal from the integrated-optical sensor is converted into a digital form to be processed is shown. The limiting sensitivity of such a waveguide-sensor cell is theoretically evaluated. Prospects of using such a type of integrated-optical sensors are discussed. © 2010 Springer Science+Business Media, Inc.