Power spectral densities of atmospheric aerosol particle counts / by Chatt C. Williamson [and others].

Format:

Book

Government document

Author/Creator:

Williamson, Chatt C.

Contributor:

U.S. Army Research Laboratory

Series:

ARL-TR (Aberdeen Proving Ground, Md.) ; 5064.

ARL-TR ; 5064

Language:

English

Subjects (All):

Atmospheric physics.

Aerosols.

Spectral energy distribution.

aerosol.

Physical Description:

1 online resource (iv, 26 pages) : illustrations.

Place of Publication:

Adelphi, MD : Army Research Laboratory, [2010]

Summary:

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.

Notes:

Title from PDF title screen (ARL, viewed Nov. 22, 2010).

"January 2010."

Includes bibliographical references.

OCLC:

574446673

Access Restriction:

APPROVED FOR PUBLIC RELEASE.