Prelim. Scat. Closure: Meas vs Pred at 550nm

Calculation notes:
Calculated scattering from size distributions using algorithm
built in to the sizing data acquisition system (Dave's Mac)
Uses look-up tables for scat and backscat for each size bin.
Sub-micron and super-micron scattering analyzed separatedly.
Assumes:
density = 1.8 g/cc, such that Daero = 1 um >>> Dgeo = 0.745 um
real refractive index = 1.45
imaginary refractive index = 0.00

All values have been converted to STP (1013.2mb, 273.2K)

Plot notes:
Each plot shows 2-days of data and four parameters:
>Sub-um Total Scatter (an extensive property)
>Sub-micron fraction of Total Scat (intensive property)
>Backscatter fraction for Sub-um (intensive)
>Backscatter fraction for Super-um (intensive)
"Pred" means predicted from the size distribution.
"Pred" values use the neph angular sensitivity function.
"Pred" values do not use the neph wavelength sensitivity functions.
"Meas" means the dry neph measurement (from John Ogren).

Conclusions:
1. For Sub-um Total Scat, "Pred" is much higher than "Meas"
and much more variable from 323.5 to 327.7. This probably
indicates a serious problem with the sizing system during this
period (we need to check out this and other possibilities.)
Note that this period immediately follows the pressure line
burst problem on day 323. Excluding this one period, agreement
is within 20% and frequenty (e.g. 329-333) well within 10%.

2. For Sub-um Backscat. Fraction, "Pred" is systematically
lower than "Meas" by 0.01 to 0.03, throughout the data set.
This is consistent with findings at CPO for both Marine
and Continental aerosols. The cause is not known, but we
DO KNOW from lab tests that the neph measures the backscat
fraction for sub-um particles accurately if particles are
really homogenous spheres.

3. For Super-um Backscat. Fraction, "Pred" is almost invariant
while "Meas" shows large variability. Again, this is
consistent with findings at CPO. Part of the variability
in "Meas" is due to noise. The lack of variability in "Pred"
indicates that the APS does not see significant changes
in the super-micron size distribution. This could be real
or it could be a problem with the APS. We will compare this
to the APS 3320 later this year. It could also be changes in
optical properties that are not reflected in the aerodynamic
size distribution.


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