Accession Number : AD0801891

Title :   A STUDY OF THE DIFFUSION OF AEROSOLS RELEASED FROM AERIAL LINE SOURCES UPWIND OF AN URBAN COMPLEX. VOLUME I.

Descriptive Note : Final rept. Jun 63-Jul 66,

Corporate Author : TRAVELERS RESEARCH CENTER INC HARTFORD CT

Personal Author(s) : Hilst, Glenn R. ; Bowne, Norman E.

Report Date : JUL 1966

Pagination or Media Count : 242

Abstract : Diffusion of aerosols over an urban complex was measured and analyzed in 21 separate experimental events. Fluorescent pigment powders were released as a quasi-instantaneous elevated line source upwind of Fort Wayne, Indiana; their distribution was measured in and above urban and rural. A mathematical model was derived. The test results identified these features of atmospheric motions in and around an isolated city: (1) when the lower (61 m) atmosphere is stable (temperature lapse rate between dry adiabatic and isothermal) the axis of the tracer cloud descends rather quickly to ground level. When temperature lapse rate is clearly positive (inversion) the tracer cloud remained about release height and slowly diffused vertically. Under unstable conditions vertical mixing is vigorous; the tracer cloud is uniformly mixed from the ground to above the vertical sampling array. (2) The enhanced surface roughness and the thermal mixing caused by the city produce an average 30 to 50 per cent more vertical mixing over the city than the rural area: increased vertical mixing causes more uniform particle dispersion. (3) Individual measurements within the city, randomly variable at a factor of about 2 and with no identifiable preferred regions of high or low dosage, imply that Ft. Wayne exemplifies a single surface anomaly for the purpose of predicting its effect on aerosol diffusion. (4) Total variability of surface dosage ranges from 0 to about 1000 units, defined as above.

Descriptors :   *DIFFUSION), (*AEROSOLS, URBAN AREAS, MATHEMATICAL MODELS, WIND, VELOCITY, ATMOSPHERIC TEMPERATURE, AIRBORNE, MEASUREMENT, SURFACE PROPERTIES, METEOROLOGICAL PHENOMENA, MIXTURES, THERMAL PROPERTIES, MOTION, AREA COVERAGE, MATHEMATICAL PREDICTION, MICROMETEOROLOGY, SAMPLING, COLLECTING METHODS, DISTRIBUTION, SCATTERING, POWDERS, FLUORESCENCE, PARTICLES.

Subject Categories : Meteorology
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE