Power Spectral Densities of Atmospheric Aerosol Particle Counts
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2010
- Accession Number
- ADA513211
Entities
People
- Chatt C. Williamson
- Cheryl L. Klipp
- Dennis M. Garvey
- Michael L. Larsen
- Steven C. Hill
Organizations
- United States Army Research Laboratory