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Mobile Monitoring Platforms for Methane Source Identification

Maya Abou-Ghanem, Abigail Koss, Omar El Hajj, & Veronika Pospisilova
TOFWERK USA

Over the past two centuries, the global atmospheric concentration of methane (CH4), a potent greenhouse gas (GHG) with global warming potential of 80 times that of carbon dioxide (CO2), has more than doubled. This increase can be attributed directly to human activities since methane emissions originate from the production and transportation of fossil fuels, agricultural practice, and the decomposition of organic waste in landfills.

Methane’s short atmospheric lifetime relative to CO2, coupled with its high potency to warm Earth’s climate, makes it a prime target for climate change mitigation strategies. As a result, numerous regional and global initiatives are focused on methane monitoring and reduction. Quick action to control methane emissions can yield a relatively fast response in terms of climate benefits, making it an important element to meet international climate goals, such as those set by the Paris Agreement. Nonetheless, the variety of methane emission sources introduces challenges when attempting to pinpoint the most critical regional contributors when using methane sensors alone. However, methane is often co-emitted with source-specific volatile organic compounds (VOCs) and volatile inorganic compounds (VICs) that can be used to help identify methane emission source regions.

Vocus Elf Aircraft Platforms for Methane Source Identification

During October and November of 2023, TOFWERK collaborated on an ongoing project with the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder and the University of Maryland funded by the Colorado Department of Public Health and Environment to identify oil and gas emissions in the Colorado Front Range on a small aircraft platform. Colorado is home to more than 40,000 active oil and natural gas wells and over 200 concentrated animal feeding operations (CAFOS) with many of these facilities centered around the Front Range. Both industries can contribute to the emission of methane, which makes source identification particularly challenging in this region. Here, we demonstrate a robust method for methane source identification by coupling methane measurements from a cavity ring-down Picarro analyzer with TOFWERK’s Vocus Elf. This compact and portable mass spectrometer, which is capable of real-time analysis of VOCs with ultra-low limits of detection, was deployed for airborne measurements on a twin-engine Cessna aircraft.

Airborne data obtained from Vocus Elf PTR-MS demonstrated that enhancements in methane concentration were often correlated with enhancements in VOC levels. The combination of this information can be used to identify the source of methane emissions. Figure 1 shows the mixing ratio time series of methane during a flight over Piceance Basin where we observe multiple methane plumes within a small geographical region. Using our Vocus Elf PTR-MS, we demonstrate that these methane plumes are also associated with aromatic VOC compounds, including trimethylbenzene, xylenes, and toluene, which suggests these emissions originated from oil and gas operations. Each pollution plume also is compositionally unique; for example, the relative ratio of trimethyl benzene to toluene in plume 1 is lower than in plume 2. These results indicate that methane is being emitted from multiple sources within the region and that the pollution plumes from these sources are also compositionally different.

Figure 1. a) parts-per-billion (ppb) mixing ratio of methane overlayed onto a Google Earth image of a flight taken over Piceance Basin and b) mixing ratios in ppb of methane (grey), trimethylbenzene (blue), xylenes (orange), and toluene (yellow), as well as the aircraft’s altitude (red) as a function of time. The dotted regions correspond to the methane enhancements observed in Figure 1a.
Figure 1. a) parts-per-billion (ppb) mixing ratio of methane overlaid onto a Google Earth image of a flight taken over Piceance Basin and b) mixing ratios in ppb of methane (grey), trimethylbenzene (blue), xylenes (orange), and toluene (yellow), as well as the aircraft’s altitude (red) as a function of time. The dotted regions correspond to the methane enhancements observed in Figure 1a.

Other events of methane enhancements were near CAFOs and correlated with acetic acid, ethanol, and toluene (Figure 2). Some of these VOC combinations have been previously reported near CAFOs [1], which suggests the methane observed in this region originates from agricultural sources.

Figure 2. a) Methane mixing ratios in ppb overlaid onto a Google Earth image of a flight taken over the Colorado Front Range and b) mixing ratios in ppb of methane (grey), acetic acid (blue), ethanol (orange), and toluene (yellow), as well as the aircraft’s altitude (red) as a function of time. The dotted region corresponds to the region shown in Figure 2a. The missing data points for acetic acid, ethanol, and toluene in plume 1 is attributed to the instrument conducting a routine background measurement during those instances.

Vocus Eiger and Vocus B Mobile Laboratory Van Platform for Methane Source Identification

TOFWERK offers different models of chemical ionization mass spectrometers tailored to measuring various compounds classes effectively. A mobile laboratory van designed for the Colorado Department of Public Health and Environment (CDPHE) equipped with two chemical ionization mass spectrometer models, the Vocus Eiger and Vocus B, a weather station and Picarro methane analyzer, was deployed for investigation of landfill emissions in the summer 2023. More details on the development of this mobile van can be found in our Vocus Mobile Laboratory: landfill odor case study application note. During this test deployment, we were able to distinguish methane emissions from a landfill and adjacent dairy farm. Figure 3a shows a time series of the methane mixing ratio obtained during a test drive in the Colorado Front Range. Using VOC and VIC measurements made by our Vocus instruments, we were able to attribute methane emissions in region 1 to landfills (Figure 3b) and region 2 to the dairy farm (Figure 3c).

The mobile lab is equipped with Vocus TWeb MOBILE software, which collates data from the two mass spectrometers, the Picarro H2S and CH4 analyzer, and the weather station (including wind speed and direction) into a single data set. The collated dataset can then be viewed on a single screen while driving (Figure 1), which simplifies post processing and facilitates comparisons of the data from different instruments (Figure 2). The concentrations of selected pollutants are depicted in real time on a map, facilitating identification and sources allocation. Furthermore, the data stream from Tweb MOBILE is also available for integration into third-party software. 

Figure 3. a) A Google Earth image with methane mixing ratios in part-per-million (ppm) measured near a landfill and dairy farm during a test drive with a mobile laboratory van in the Colorado Front Range and b) concentration in ppb as a function of drive time for toluene (orange) measured by a Vocus Eiger, methane (blue) measured by a Picarro analyzer, and acetic acid (yellow) measured by a Vocus Aim “B” near a landfill and c) concentration in ppb as a function of drive time for lactic acid (blue) measured by a Vocus Aim “B”, toluene (orange) measured by  a Vocus Eiger PTR, methane (brown) measured by a Picarro analyzer, and ammonia (green) measured by a Vocus Aim “B” near a dairy farm.
Figure 3: a) A Google Earth image with methane mixing ratios in part-per-million (ppm) measured near a landfill and dairy farm during a test drive with a mobile laboratory van in the Colorado Front Range and b) concentration in ppb as a function of drive time for toluene (orange) measured by a Vocus Eiger, methane (blue) measured by a Picarro analyzer, and acetic acid (yellow) measured by a Vocus B near a landfill and c) concentration in ppb as a function of drive time for lactic acid (blue) measured by a Vocus Aim “B”, toluene (orange) measured by  a Vocus Eiger, methane (brown) measured by a Picarro analyzer, and ammonia (green) measured by a Vocus B near a dairy farm.

Conclusion

This application note demonstrates successful deployment of a suite of TOFWERK’s Vocus chemical ionization mass spectrometers on mobile platforms and highlights the utility of these measurements for methane source identification. Our innovative approach utilizes both aircraft and vehicle platforms to conduct mobile VOC and VIC measurements, enabling precise identification of methane sources across diverse industries such as oil and gas operations, landfills, and agricultural practices. As the landscape of methane reduction, regulation, and compliance evolves, accurate source identification becomes increasingly crucial. Further, this innovative approach could be applied to other airborne pollutants or issues linked to adverse air quality. Beyond methane, source apportionment based on presented data can become essential in detecting odors emanating from various industrial and agricultural processes, characterizing urban pollution to discern levels of specific toxics, or distinguishing between diesel and gasoline vehicle emissions based on their unique chemical signatures. This adaptive methodology could play a critical role in environmental protection efforts, enabling more informed and responsive strategies for regulation and mitigation.

References

[1] Yuan, Bin, et al. “Emissions of volatile organic compounds (VOCs) from concentrated animal feeding operations (CAFOs): chemical compositions and separation of sources.” Atmospheric Chemistry and Physics 17.8 (2017): 4945-4956.