conditions. The second ‘reference’ electrode is not exposed to air, and is
therefore only sensitive to the cell’s operating conditions. By comparing
these two signals, the response from gas analyte concentrations can be
isolated.
1.2.1. Black carbon (BC) compensation
While hardware features contribute significantly to correcting the
ObservAir’s environmental dependence, some BC measurement artifacts
remain that must be corrected by software. This software compensation
centers on DSTech’s proprietary environmental training approach. Prior
to delivery, all ObservAir units sample filtered air for at least 24 hours
while being subjected to fluctuating environmental conditions. Using the
data collected during this training period, the unique environmental
dependence of each ObservAir’s absorption photometer is modeled
mathematically. The models are uploaded to each unit, and used to
correct BC concentration measurements in real-time. Each ObservAir is
delivered with its own unique zero-calibration sheet, as shown in Figure 4
below. The calibration sheets show the sensor’s baseline environmental
dependence and black carbon measurement performance both before and
after compensation. The sensor also carries out regular calibration and
diagnostic checks of the underlying electronics, and includes other
software features to maintain and validate photometer performance.
Figure 4. Each ObservAir comes with its own zero-calibration sheet
Details regarding the onboard BC compensation algorithm and it’s
derivation can found in the publication below. Please note that this
publication describes the operation of the Aerosol Black Carbon Detector
(ABCD), an academic prototype of the ObservAir. The underlying
compensation methods and principles remain the same as that shown in
the publication, although experimental procedures and data processing
have been significantly improved in the ObservAir.
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