Design, build and initial tests of a portable methane measurement platform

The quantification of methane concentrations in air is essential for the
quantification of methane emissions, which in turn is necessary to
determine absolute emission and the efficacy of emission mitigation
strategies. These are essential if countries are to meet climate goals.
Large scale deployment of methane analyzers across the millions of
emission sites is prohibitively expensive and lower-cost instrumentation
has been recently developed as an alternative.  Currently, it is
unclear how cheaper instrumentation will affect measurement resolution or
accuracy.  To test this, the Wireless Autonomous Transportable
Methane Emission Reporting System (WATCH4ERS) has been developed and
comprises four commercially available sensing technologies: Metal Oxide
(MOx,); Non-dispersion Infrared (NDIR); Integrated Infrared (INIR); and
Tunable Diode Laser Absorption Spectrometer (TDLAS).  WATCHERS is
the accumulated knowledge of several long-term methane measurement
projects at Colorado State University’s Methane Emission Technology
Evaluation Center (METEC) and this study describes the integration of
these sensors to a single unit and reports initial instrument response to
calibration procedures and controlled release experiments. Specifically,
this paper aims to describe the development of the WATCH4ERS unit, report
initial sensor response, and describe future research goals, while future
work will use data gathered by multiple WATCH4ERS units to 1. better
understand the cost-benefit balance of methane sensors, and 2. identify
how decreasing instrumentation costs could increase deployment coverage
and therefore inform large‐scale methane monitoring strategies. 
 Both calibration and response experiments indicate the INIR has
little practical use for measuring methane concentrations less than 500
ppm.  The MOx sensor is shown to have a logarithmic response to
methane concentration change between background and 600 ppm but it is
strongly suggested that passively sampling MOx sensor cannot respond fast
enough to report concentrations that change on a sub-minute time
frame.  The NDIR sensor reported linear change to methane
concentration between background and 600 ppm, although there was a
noticeable lag in reporting changing concentration especially at higher
values, and individual peaks could be observed throughout the experiment
even when the plumes were released 5 s apart.  The TDLAS sensor
reported all changes in concentration but remains prohibitively
expensive.  Our findings suggest that each sensor technology
could be optimized by either operational design or deployment location to
quantify methane emissions and the WATCH4ERS units will be deployed in
real-world environments to investigate the utility of each in the future.

The WATCH4ERS comprises five individual
methane sensors (two MOx sensors, NDIR sensor, INIR sensor and a TDLAS)
that stream data to a single laptop PC via a powered USB hub.  Data are
read into the PC using Python code and data are stored locally.
  The code required to run the
WATCH4ERS can be found at https://github.com/stuartnriddick/AMMMU.git.  Three Arduino UNO’s are used to interface the MOx sensors, the ’46 Hawk (TDLAS sensor) and the environment monitoring sensor (DHT22) to the data logging PC through a standard USB port. For the TGS2600 and TGS2611 metal oxide sensors, an Arduino UNO along with an Adafruit ADS1115 ADC interfaces the sensors and the code “Riddick MOX Arduino Code.ino” controls the sampling of these sensors and the transfer of the data to the PC.  The ’46 Hawk sensor does not have any digital output and the data from this instrument is extracted by a technique known as “data sniffing” where code run by the monitoring Arduino interrogates the ’46 Hawk LCD and extracts the values displayed on the LCD.  Sniffing the data transmitted to the LCD screen of the ’46 Hawk requires “Hawk Arduino Code.ino” downloaded to the Arduino UNO connected to it.  The other two sensors, the INIR and the NDIR both have serial RS232 interfaces and these outputs are converted using RS232 to USB converter modules plugged directly into the USB Hub. The Python code that collects data from all the sensors and writes them to a file is “Ammu Python Code.py”.  

# Design, build and initial tests of a portable methane measurement
platform
[https://doi.org/10.5061/dryad.gf1vhhn0j](https://doi.org/10.5061/dryad.gf1vhhn0j) ## Description of the data and file structure An experiment was conducted where 0.5% methane was released at 5 liters per minute 0.5 m upwind of a WATCH4ERS unit.  Air flow between the release point and the WATCH4ERS unit was controlled at 3.5 m s-1 using a fan blowing at a constant rate.  Five experiments were conducted to investigate the response of the MOx, NDIR, INIR and TDLAS sensors.  In each experiment, three gas plumes were released from a cylinder for a fixed duration with a controlled time between the plume release.  The aims of the experiment are to determine: 1. How many of the plumes could be seen in the instruments’ methane concentration data; 2. The typical time taken to respond to a downwind plume; and 3. The typical methane concentrations observed downwind. ### Files and variables #### File: Riddick\_WATCH4ERS\_-\_Data.xlsx **Description:**  ##### Variables * Time: Time presented as the portion of a date value and represented by a decimal number. * TDLAS CH4 concentration (ppm): Methane enhancement as measured by the TDLAS in units of parts per million. * NDIR CH4 concentration (ppm): Methane enhancement as measured by the NDIR sensor in units of parts per million. * MOx CH4 concentration (ppm): Methane enhancement as measured by the metal oxide sensor in units of parts per million. * Gas on: Timing and duration of the controlled release gas being turned on and off.  10 represents on and 0 represents off. ## Code/software The data are presented in .xlsx format.