A New Instrument for Evaluating the Visual Quality of Air

Any device for assessing the visual quality of air must necessarily have an extremely high sensitivity since, at times, the Rayleigh scattering of air molecules is the determining factor. The integrating nephel-ometer of Brewer and Beuttell has been adapted for air quality measurement. It records the volume scattering coefficient and was reliable in over a month of continuous operation. The results may be interpreted in terms of visual range; if so the inherent noise in the system corresponds to more than 500 miles visual range with a 100-second response time. The low cost, simplicity, and sensitivity of the device make it appear useful for rapid evaluation of visual air quality. The design of the instrument will be presented, including both the optical and electronic components. The results of operation of the instrument in Seattle during days of moderate air pollution will be used to illustrate the utility of the device.