COMPARISON OF OPEN-PATH AND POINT MEASUREMENTS OF A GASEOUS POLLUTANT IN THE VICINITY OF A MODEL BUILDING

摘要

Field experiments were carried out in the vicinity of an isolated building using open-path and point monitoring air pollution detectors to measure concentrations of a tracer gas released from a source located either on the building or at the downwind face of the building. Experiments were conducted under neutral or slightly unstable weather conditions. Either three or five fast-response point monitors were located along the beam path of an open-path instrument, in the wake of the building. Experiments were performed with different source locations, detector locations and building orientations to the wind. Visual comparison of data time series showed that data from the two types of instruments followed similar trends. The best degree of correlation occurred for an averaging time similar to the response time of the open-path monitor. Mean concentrations detected by the open-path instrument were generally in very good agreement with the path averaged mean concentrations from the point monitors. The point monitors were also capable of providing time-resolved data needed to describe detailed concentration fluctuation statistics.