Appen dix A: Calc ulating Flow Rate
Airmetrics
63
(3)
Where
I
sp
=
flowm eter set poin t, liters/minu te
P
std
=
standard atmospheric pressure, 760 mm Hg
T
std
=
standard temperature, 298 K°
P
act
=
actual ambient pressure, mm Hg
T
act
=
actual ambient temperature, K°
Airmetrics MiniVol Users Guide
64
Airmetrics
(4)
(5)
PM Concentration Calculation
To calculate the P M conc entration for a sam ple taken with the MiniVo l sampler,
the volume o f air that passed throug h the filter at standard cond itions,
V
std
, or at
ambient con ditions,
V
amb
, must be calculated . This is m ost easily d one in a m ulti-
step procedure (the example that follows uses Sampler 2318 whose calibration
sheet is shown in Figure A.1):
1.
Calculate the air flow rate at ambient co nditions,
Q
act
, using Equation 4. The
slope,
m
vol
, and intercept,
b
vol
, of the sampler calibration are obtained from the
calibration sheet. For S ampler 231 8,
m
std
= 1.0011 and
b
std
= 0.0826. The
units of Q
std
are
liters/minu te
.
2.
Calculate the volume of air that passed through the filter during the sampling
period at actual am bient conditions,
V
act
(in cubic meters).
where
t
hr
= sam pling period, in hou rs
In the equation above, time is expressed in hours since the MiniVol's elapsed
time meter rec ords time in hou rs. The units of V
act
are
cubic meters
.
In the actual use of the portable samplers, the
temperatures
,
pressures
and
flowmeter readings
are only noted at the start (when the sam pler is set up for a
run) and end (when sampler is retrieved) of the sampling period. Therefore,
calculate Q
act
for the starting and ending conditions and use the average Q
act
to
determine V
act
.
3.
To calcu late the con centration at standard condition s, correct th e volum e of air
at actual ambien t conditions,
V
act
, to the volume of air at standard conditions,
V
std
:
