Near-Field Characterization of Methane Emission Variability from a Compressor Station Using a Model Aircraft

Abstract

A model aircraft equipped with a custom laser-based, open-path methane sensor was deployed around a natural gas compressor station to quantify the methane leak rate and its variability at a compressor station in the Barnett Shale. The open-path, laser-based sensor provides fast (10 Hz) and precise (0.1 ppmv) measurements of methane in a compact package while the remote control aircraft provides nimble and safe operation around a local source. Emission rates were measured from 22 flights over a one-week period. Mean emission rates of 14 ± 8 g CH4 s(-1) (7.4 ± 4.2 g CH4 s(-1) median) from the station were observed or approximately 0.02% of the station throughput. Significant variability in emission rates (0.3-73 g CH4 s(-1) range) was observed on time scales of hours to days, and plumes showed high spatial variability in the horizontal and vertical dimensions. Given the high spatiotemporal variability of emissions, individual measurements taken over short durations and from ground-based platforms should be used with caution when examining compressor station emissions. More generally, our results demonstrate the unique advantages and challenges of platforms like small unmanned aerial vehicles for quantifying local emission sources to the atmosphere.

Unmanned Aerial Systems for Monitoring Trace Tropospheric Gases

“…There are further examples of sensors used for trace gas deployment that do not explicitly stick to one type of detection mechanism, several examples of UAS deployments for atmospheric monitoring can be found in the literature [46][47][48][49][50][51][52][53][54]. For calibration purposes, the measured resistivity of the MQ-4 sensor (R s ) is expressed relative to the reference signal for 1000 ppmv CH 4 in air (R o ) [43].…”

Simultaneous multicopter-based air sampling and sensing of meteorological variables

“…In addition, de Boer et al (2016) implemented radiation and aerosol size distributions sensors, Altstädter et al (2015) focused on ultrafine particles and Båserud et al (2016) showed the possibility of turbulence measurements. Nathan et al (2015) measured methane with an in situ sensor flying around a compressor station to calculate its emissions. The importance of knowing both meteorological conditions and methane (or aerosols, particulate matter, etc.)…”

Lightweight mid-infrared methane sensor for unmanned aerial systems

“…In particular, small (<25 kg) UAS have low operation costs, relaxed regulatory requirements, and can operate near the surface, where most emissions originate. As an example, a near-infrared sensor (100 ppbv precision) equipped on a remote-controlled helicopter has been used to estimate the magnitude and temporal variability of methane emissions from a natural gas compressor station [4], and serves as an alternative to mobile laboratory and ground survey techniques which are more time-consuming or may miss elevated leak sources.…”

“…More compact methane sensors are available that typically either use standoff detection for path integrated measurements [9,10], or have been targeted at high concentrations such as for direct sampling from natural gas leaks. In addition, several lightweight in situ methane sensors have previously been demonstrated for high-altitude balloon-borne or small UAS use [4,11,12]. These employed an open-path design, where air flows directly into the optical cell rather than using sampling equipment allowing for low weight and inherently high time response [7].…”