Appen dix B: Gra vimetric An alysis Proc edure
Airmetrics
75
reading. Average flow in liters per minute is the mean of the start and stop
flow conversions.
The sample time (
t
) is ordinarily the difference between the start and stop
readings from a time totalizer. It is convenient to record time in minutes,
the unit used for flow, to simplify the calculations.
Sample air volume (
V
), in cubic meters, is then the average flow (
Q
), in
liters per minute, times the sample time, in minutes, times 0.001, the
conversion from liters to cubic meters.
3.
The information from the field sampling report and weights from the filter
weighing book are entered in the sample log book. Data run assumes
midnight-to-midnight samples; if otherwise, the times and dates must be
clearly ind icated. D ate receive d is whe n logged into the lab. T he station is
indicated by A IRS/SAR OAD number. Sa mpler and filter num bers are
copied from the field report. Type refers to filter medium, in this case
Whatman QM-A Quartz Microfibre. Configuration indicates the kind of
sample, in this case TSP or PM
10
. Orifice nu mber, a verage flo w, and a ir
volum e (V) are e ntered from the field rep ort. Finally, th e particulate
matter concentration (
PM
) in micrograms per cubic meter is found by the
formula:
where the "1000" is the conversion factor from m illigrams to micrograms.
4.
Final concentration data is reported to AQC in the AIRS/SARO AD format
for entry in the appropriate data base.
5.
A sample day station summary is compiled for all sites listing filter
numbers and air volume. The information is needed to cross reference
sample s by date a nd station. T he sheet is also used to record v oids, sam ple
losses an d other pro blems. O nce this sh eet is com pleted, the field
sampling report may be filed.
Airmetrics MiniVol Users Guide
76
Airmetrics
6.
The computer program used to calculate particulate matter concentrations
from portable saturation samplers has expanded data flagging and calcula-
tion feature s which allow for e quipm ent limitatio ns and d ata quality
assumptions appropriate for survey sampling.
a.
Concentration calculations can be performed, and flagged with a
codes denoting data limitations or assumptions included in the
calculations. A listing of commonly used codes is presented below.
M :
Missin g field data
B:
Battery failure
F:
Flow differential
T:
Timer malfunction
S:
Sampler malfunction
D:
Damaged filter
b.
The sampler flowrate differential flag (
F:
) is computer-generated, and
is attached to the calculated concentration if the pre- and/or post-flows
are outside ± 15% of the samplers "ideal flow setpoint". In this case
the pre-flow is used to calculate the particulate matter concentration.
c.
Sometimes, a final flow is not available due to battery failure of the
portable sampler. In this case, a "
B:
" code is assigned to the data, and
a post flow equal to the pre-flow is used to calculate the concentra-
tion. This provides some assurance that the actual flowrate will be
overestimated , and the resultant con centration biased low er.
d.
The oth er codes are assign ed based on com ments m ade on fie ld data
sheets, or observations of the filters during post weighing procedures.
Flagged data and comm ents are included in the printed calculations,
and printed in tabular form appended to the project data summary.
D. Quality Control and Assurance
1.
At least a 7% level of blanks shall be set aside during prep aration of filters
for samp ling. The blank is w eighed, a ssigned a numb er in sequ ence w ith
the other filters being tared, then placed in a labeled petri dish. The code
letter B is prefixed to the filter number in the weighing book and on the
