Principles of Operation:
The MASP determines the size and concentration of particles from 0.3
to 20 micrometers (um) diameter and the index of refraction for
particles 0.4 to 0.7 um in diameter. The light scattered from
individual particles passing through a 0.780 um wavelength laser beam
is collected by optics over angles of 30-60 degrees in the forward
direction and in the backward direction 120-150 degrees. The index of
refraction is determined by comparing the ratio of forward to
backscattered to the total scattered light and finding the best fit to
Mie scattering theory. The size of the particle is determined from the
total scattered light once the refractive index is determined.
The shrouded inlet of the probe minimizes angle of attack airflow distortion
and maintains isokinetic flow through the sensing volume so that particle
volatilization is minimized.
Scientific Objectives:
The radiative balance of the earth is dependent upon the amount of solar
radiation that is reflected or absorbed. Aerosol particles play an important
role in this process as they reflect solar shortwave radiation, absorb
terrestrial longwave radiation and are also the source of cloud droplet and
ice crystal nuclei. These latter particles have an even greater effect on
the earth's radiation budget. Aerosol particles also serve as the site for
heterogeneous chemical reactions in both the troposphere and stratosphere.
The radiative properties of aerosols and their effectiveness as sites for
heterogeneous reactions depend upon the particle size, shape and refractive
index. The MASP measures these characteristics and will contribute to a
better understanding of the microphysical and optical properties of
tropospheric and stratospheric particles in our atmosphere.
Darrel Baumgardner
Last modified: Wed July 5 2000 1:13pm tac