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OBSERVATIONAL STUDY OF TRANSPORT IN THE FREE TROPOSPHERE
Citation:
Ching, J.K.S., E. Uthe, B. Morley, AND W. Viezee. OBSERVATIONAL STUDY OF TRANSPORT IN THE FREE TROPOSPHERE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/D-84/300.
Description:
Anthropogenic pollutants such as acidic precursors, oxidants and particulates can arrive above a convective mixed layer by penetrative convective cloud activity (venting) or by air mass convergence. The development of improved long-range transport models will require consideration of the transport and dispersion processes in both the mixed and free tropospheric layers. These processes in the free troposphere are not adequately documented or understood and are generally ignored in current trajectory calculation schemes and source to receptor models. To address this problem, a technique to track free tropospheric pollutant transport was recently developed. The feasibility of using airborne lidar to observe the three-dimensional distribution of fluorescent dye particle (FDP) tracers in long-range atmospheric transport and dispersion studies as a candidate approach has been successfully demonstrated in field experiments conducted in the North East U.S. during October 1983. This approach uses a lidar system to excite non-toxic fluorescent dye particle (FDP) released into the atmosphere, and to monitor the emitted fluorescent light. When the lidar receiver is spectrally filtered, the fluorescent light can be detected separately from the elastic backscattered signal by background aerosols. On one occasion, an FDP cloud was released above the mixing layer, and subsequently tracked over more than 300 km. On another occasion, an initially-released circular tracer cloud reached an 8-to-1 (16-to-2 km) length-to width ratio two hours after release, and a 12-to-1 (30-to-2.5 km) length-to width ratio about four hours after release.