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ObservAir
Operating Manual
5.4.
Operational settings for common applications
Table 9 provides typical BC concentrations and operational settings for
some common sampling scenarios. Note that the guidance provided is
approximate and mostly meant to serve as an illustrative guide: Some
applications may not be well described/served by the parameters listed.
Table 9.
General settings for several monitoring applications
•
Ambient monitoring:
When deploying the ObservAir as a static network
node over long periods (weeks or months), the flow rate should be set
as low as possible to maximize filter life and reduce the maintenance
effort, especially when network sites are remote or numerous. Ambient
monitoring applications typically require data with low temporal
resolution – hourly measurements are often sufficient – and this helps
reduce the flow rate requirements. Referring to Table 8, it can be seen
that the minimum flow rate setting of 25 ccm provides suitable hourly
measurements for nearly all BC concentrations. However, it should be
noted that this achieves a nominal BC measurement resolution that is
~10% of the average concentration, which may not be sufficient for all
applications (e.g., regulatory monitoring). If greater resolution is desired,
flow rate should be increased to the values listed in Table 9. Similarly,
special consideration should be given when conducting long-term
monitoring in rural or remote areas with BC concentrations < 0.5
µ
g/m
3
. In these scenarios when filter loading is low, it is generally
advisable to operate the sensor at a high flow rate setting (100 to 200
ccm) to maintain BC measurement integrity.
Average BC
(
µ
g/m
3
)
Flow rate
(ccm)
Time
Resolution
Filter life
Ambient:
Background/rural
Low
(0 to 1)
High
(100 to 200)
Low
(1 hour)
High
(Weeks/Days)
Ambient:
Typical
Medium
(0.3 to 5)
Medium
(50 to 100)
Low
(1 hour)
High
(Weeks/Days)
Ambient:
Dense Urban
High
(5 to 50)
Low
(25 to 50)
Low
(1 hour)
Medium
(Days)
Emissions capture
(direct source)
Extreme
(> 100)
Medium
(50 to 100)
Medium
(10 to 60 sec)
Very low
(Hours)
Mobile/Personal
Medium/High
(0.3 to 50)
High
(100 to 200)
High
(2 to 10 sec)
Low
(1 day)
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ObservAir
®
Operating Manual
•
Emissions source characterization:
The ObservAir can be configured to
characterize emissions from stationary exhaust stacks, vehicle tailpipes
and other pollution sources. When sampling emissions directly, do not
exceed the ObservAir’s maximum temperature, relative humidity range,
and pollution concentration ratings (Table 3). As with other instruments,
the ObservAir may require that emissions from the source be diluted,
cooled, and/or dried. For transient monitoring applications, such as
engine testing, measurements are typically required every 2 to 10
seconds, and therefore the ObservAir’s sample flow rate must usually
be set >100 ccm to maintain adequate measurement resolution. When
sampling over long periods (stack monitoring over hours or days), the
sample flow rate may be lowered to 25 or 50 ccm to maximize filter
life, especially when concentrations are highly elevated. Sampled
concentrations depend on the source and flow conditioning system
implemented (e.g. diluter), but it is not unusual for BC concentrations
to exceed 100
µ
g/m
3
when capturing emissions directly.
•
Mobile monitoring:
When sampling from a mobile platform,
measurements must be logged as fast as possible to maintain adequate
spatial resolution required for the air pollution maps that are ultimately
generated. Therefore, the ObservAir should be configured to log
concentration data every 2 to 10 seconds at the maximum flow rate
setting of 200 ccm to maximize the temporal resolution of both BC and
gas concentration measurements. Always operate the ObservAir inside
the mobile platform (e.g. car or van) with an electrically conductive
sample line running outdoors. Do not mount sensors on the exterior of
mobile platforms without the dedicated DST mount and enclosure.
When mounting the ObservAir inside the mobile monitoring platform,
take care to minimize exposure to mechanical vibrations, excessive heat
and/or direct sunlight over extended periods.
•
Personal monitoring:
Personal monitoring guidelines largely mirror
those provided for the mobile platform: Operate the sensor at a high
sample flow rate (100 to 200 ccm) to maximize the quality of BC
measurements collected every 2 to 10 seconds. Depending on the
application and concentrations sampled, some consideration may be
given optimizing the flow rate for filter life (e.g., each filter lasts a full 8-
hour workday). The sensor may be mounted inside a bag or from a
strap (such as those provided by DST), but take care to clip an
electrically conductive sample line to the subject’s lapel or other
appropriate location.