treasure valley road dust study: final report - ResearchGate

3.2.4.1 Data Acquisition
The TRAKER may utilize up to 10 instruments (6 DustTraks, 3 PSAs, and a GPS), each
generating data at a rate of up to 60 readings per minute. A central onboard computer is used to
capture the data in real-time as it is generated. Data from individual instruments are transferred
via RS-232 serial interfaces to a multiplexing unit that is in turn connected to the computer.
Specialized software has been written to capture the data, use the computer clock to provide a
common time stamp, write to a database in real-time, and provide the operator(s) with feedback
regarding the status of instruments. An example of the TRAKER display panel is shown in
Figure 3-4.
The data capture software was not available for use during the winter portion of the
study. Data generated from onboard instruments were captured using the dataloggers that are
built into individual instruments. Data were then periodically downloaded to the central
computer manually. The TRAKER control panel was available for the entire summer field
study.
3.2.4.2 Real-Time Measurement Documentation
In addition to collecting data from onboard instruments, the TRAKER central computer
also provides a means to document road conditions. An example of the automated form used to
document TRAKER measurements is given in Figure 3-5. The characterization of road
conditions is achieved through a set of “Hot Keys” on the keyboard. Provisions have been made
for “medium duration” conditions (such as the type of road shoulder and the lane of travel) and
“short duration” conditions (such as passing a construction area or an intersection with an
unpaved road). Road conditions are automatically written to a database with a computer time
stamp, allowing for cross-referencing with the TRAKER measurement. The TRAKER
documenter was used in the Treasure Valley Road Dust Study on an experimental basis only.
3.3 TRAKER QA
In this section, we discuss the procedures used to characterize the TRAKER
measurement, accuracy, and response to various conditions. We describe the measurement range
and precision of the TRAKER, the loss of particles in the inlet sample line, the effect of diluting
the sample stream in the inlets, and the effect of vehicle speed on the TRAKER signal.
3.3.1 Measurement Range, Precision, and Out of Range Data
The DustTrak instrumentation onboard the TRAKER vehicle has a precision of 1 ?g/m 3 .
Thus, the smallest measurable difference in concentration between the tire and the background
monitors is 1 ?g/m 3 . As described in Section 3.5, this corresponds approximately to a singlepoint
minimum detection limit equivalent to an emissions fac tor of 0.9 g/VKT, meaning that any
1-second measurement can only be resolved to within this value. Note that substantially smaller
emissions factors can be measured with the TRAKER if multiple points are used to calculate an
average. At the other end of the measurement range, DustTrak readings above 150 mg/m 3 are
not reliable. This corresponds to an emissions factor for PM 10 of approximately 50 g/VKT.
Note that the upper end of the range can be extended to 110 g/VKT if the optional dilution
system is in use (Section 3.2.2). This upper limit can be further extended to 160 g/VKT if the
ratio of PM 2.5 to PM 10 DustTrak measurements is utilized (see section 3.3.1.1).
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