exceed the ObservAir’s maximum temperature, relative humidity range,
and pollution concentration ratings (Table 2). 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 µg/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 DSTech 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 DSTech), but take care to clip an electrically conductive
sample line to the subject’s lapel or other appropriate location.
5.5. Indoor/Outdoor monitoring guidelines
The ObservAir can be operated in nearly any indoor environment without
modification: The sensor is plugged into a power source and set to run for
as long as needed. Exposure to direct sunlight should be avoided over
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