~~~~Bap_corr = Bap_raw / FloCorFac * STPfac~~~~
where, FloCorFac corrects manufacturer's flow meter
and STPfac = T/273.2*1013.2/P.
STP UW: used neph inlet temperature and neph pressure
from file nm_X.bnd provided by John Ogren. This file had only
3 or 4 points per hour, so I used the closest one.
STP UIUC: done by John Ogren. I do not know exactly what
pressure and temperature measurements were used.
Flow UW: Actual flows were measured with a BIOS volumetric
flow meter and compared to the flows reported by the PSAP's on the
front panel. This was done at the beginning and end of the campaign,
with very consistent results. To wit:
~~~~98/11/15 UW panel=0.370 BIOS=0.506 FloCorFac=1.366
~~~~98/12/01 UW panel=0.426 BIOS=0.582 FloCorFac=1.366
~~~~98/11/15 UIUC panel=0.414 BIOS=0.544 FloCorFac=1.315
~~~~98/12/01 UIUC panel=0.460 BIOS=0.599 FloCorFac=1.302
Flow UIUC:The UIUC flow correction was applied by John
Ogren. This relied on the flow measurement made by Mike Bergin
in October, 1998 (not the values for UIUC above). I do not know
the exact value of this flow correction factor.
PLUMBING:
UW PSAP was installed in parallel with the existing, UIUC unit.
Both units had the same inlet and impactors upsteam and the same
vacuum pump downstream. The UW unit was on the 90-degree branch
of a stainless 1/4" Tee. Flow rates were approximately 0.5 LPM
to both units. The automatic ball valve switched the flow to
go through or bypass the 1-micron (aero dia) impactor every 10
minutes. (i.e. 20-minutes for complete cycle)
FILTERS:
The UW unit used the standard filter holder with inner O-rings
removed. This is how the UW unit was operated during lab and
field intercomparison tests with other PSAP's and also during
calibration tests in Seattle. The UIUC unit used the new, piston
style filter holder that takes two 1 cm filters. This style has
not been tested as extensively in the lab, but limited tests in
Seattle showed no significant difference between the standard and
the new style of filter holder. For both units, filters were
changed daily by Mike Snyder of Illinois Water Survey. Both sets
of filters showed nice, sharp spots, indicating no leak problems.
DATA LOGGING:
UW unit was set to 300 second averaging and digital data was sent
every 10 minutes to the UW Mac computer logging the size distribs.
With a 10-minute coarse/fine switching time, this means that the
UW data corresponds to a 5-minute average over the latter half of
each 10-minute period. We use the Bap level reported by the PSAP
(not the signal and reference counts). The raw Bap is adjusted
for filter-transmission and the manufacturer's calibration but is
NOT adjusted for error in the measured flow. We apply this flow
adjustment during data processing.