Accession Number : ADA513211


Title :   Power Spectral Densities of Atmospheric Aerosol Particle Counts


Descriptive Note : Final rept. 2008-2009


Corporate Author : ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD COMPUTATIONAL AND INFORMATION SCIENCES DIR


Personal Author(s) : Williamson, Chatt C. ; Hill, Steven C. ; Garvey, Dennis M. ; Larsen, Michael L. ; Klipp, Cheryl L.


Full Text : http://www.dtic.mil/get-tr-doc/pdf?AD=ADA513211


Report Date : JAN 2010


Pagination or Media Count : 32


Abstract : The velocity components of the atmospheric wind typically have a power spectral density (PSD) with a slope of -5/3 in an "inertial subrange" of frequencies, roughly from 0.01 to >10 Hz depending on the wind speed and stability. As passive scalars, atmospheric temperature and humidity have a relatively small direct effect on the winds, and they also typically have a -5/3 slope in this frequency range. Atmospheric aerosol particles are also expected to behave as passive scalars, and PSD slopes of -5/3 have been reported for some atmospheric aerosol measurements with a volume-based light-scattering instrument. Herein, we present aerosol measurements obtained with a single-particle optical counter over two four-day periods with concurrent sonic anemometer measurements of wind speed and temperature. PSDs of the aerosol particle counts, temperature, and winds are presented and compared in the frequency range 10(exp-4) to 10 Hz for 5 min subintervals. As expected, the PSDs of the velocity components and of the temperature decrease with a slope near the predicted -5/3. But the slopes of the PSDs of the aerosol particle counts are near -5/3 for only a small fraction of the subintervals; generally the magnitude of the slopes is much smaller than -5/3 and often close to zero. The discrete nature of the particle counts results in a shot-noise floor, which limits the slopes in PSD that can be measured at low particle concentrations and high sample rates. Interestingly, an overall slope of -7/6 is found over a large frequency range when the entirety of both of the four day periods is considered.


Descriptors :   *AEROSOLS , *ATMOSPHERIC PHYSICS , ATMOSPHERIC TEMPERATURE , LIMITATIONS , WIND VELOCITY , SPECTRAL ENERGY DISTRIBUTION , SLOPE STABILITY , ANEMOMETERS , HUMIDITY , LIGHT SCATTERING , FREQUENCY , CONCENTRATION(COMPOSITION)


Subject Categories : ATMOSPHERIC PHYSICS
      PHYSICAL CHEMISTRY
      ATOMIC AND MOLECULAR PHYSICS AND SPECTROSCOPY


Distribution Statement : APPROVED FOR PUBLIC RELEASE