A tracer release experiment to investigate uncertainties in drone-based emission quantification for methane point sources

Abstract. Mapping trace gas emission plumes using in-situ measurements from unmanned aerial vehicles (UAV) is an emerging and attractive possibility to quantify emissions from localized sources. Here, we present the results of an extensive tracer-release experiment in Dübendorf, Switzerland, which was conducted to develop an optimal quantification method and to determine the related uncertainties under various environmental and sampling conditions. Atmospheric methane mole fractions were simultaneously measured using a miniaturized fast-response Quantum Cascade Laser Absorption Spectrometer (QCLAS) and an Active AirCore system mounted on a commercial drone. Emission fluxes were estimated using a mass-balance method by flying the drone-based system through a vertical cross-section downwind of the point-source perpendicular to the main wind direction at multiple altitudes. A refined kriging framework, called cluster-based kriging, was developed to spatially map individual methane measurement points into the whole measurement plane, while taking into account the different spatial scales between background and enhanced methane values in the plume. We found that the new kriging framework resulted in better quantification compared to ordinary kriging. The average bias of the estimated emissions was −1 % and the average residual of individual errors was 54 %. Direct comparison of QCLAS and AirCore measurements shows that AirCore measurements are smoothened by 20 s and temporally shifted and stretched by 7 s and 0.06 seconds for every second of QCLAS measurement, respectively. Applying these corrections to the AirCore measurements and successively calculating an emission estimate shows an enhancement of the accuracy by 3 % as compared to its uncorrected counterpart. Optimal plume sampling, including the downwind measurement distance, depends on wind- and turbulence conditions and it is furthermore limited by numerous parameters such as the maximum flight time, and the measurement accuracy. Under favorable measurement conditions, emissions could be quantified with an uncertainty of 30 %. Uncertainties increase when wind speeds are below 2.3 m s−1 and directional variability is above 33°, and when the downwind distance is above 75 m. In addition, the flux estimates were also compared to estimates from the well-established OTM-33A method involving stationary measurements. A good agreement was found, both approaches being close to the true-release and uncertainties of both methods usually capturing the true-release.

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Spatial scale-dependent land–atmospheric methane exchanges in the northern high latitudes from 1993 to 2004

Biogeosciences ◽

10.5194/bg-11-1693-2014 ◽

2014 ◽

Vol 11 (7) ◽

pp. 1693-1704 ◽

Cited By ~ 20

Author(s):

X. Zhu ◽

Q. Zhuang ◽

X. Lu ◽

L. Song

Keyword(s):

Spatial Heterogeneity ◽

Spatial Scale ◽

Water Table ◽

Spatial Scales ◽

Grid Cell ◽

High Latitudes ◽

Atmospheric Methane ◽

Ch4 Emissions ◽

Biogeochemical Models ◽

Macro Scale

Abstract. Effects of various spatial scales of water table dynamics on land–atmospheric methane (CH4) exchanges have not yet been assessed for large regions. Here we used a coupled hydrology–biogeochemistry model to quantify daily CH4 exchanges over the pan-Arctic from 1993 to 2004 at two spatial scales of 100 km and 5 km. The effects of sub-grid spatial variability of the water table depth (WTD) on CH4 emissions were examined with a TOPMODEL-based parameterization scheme for the northern high latitudes. We found that both WTD and CH4 emissions are better simulated at a 5 km spatial resolution. By considering the spatial heterogeneity of WTD, net regional CH4 emissions at a 5 km resolution are 38.1–55.4 Tg CH4 yr−1 from 1993 to 2004, which are on average 42% larger than those simulated at a 100 km resolution using a grid-cell-mean WTD scheme. The difference in annual CH4 emissions is attributed to the increased emitting area and enhanced flux density with finer resolution for WTD. Further, the inclusion of sub-grid WTD spatial heterogeneity also influences the inter-annual variability of CH4 emissions. Soil temperature plays an important role in the 100 km estimates, while the 5 km estimates are mainly influenced by WTD. This study suggests that previous macro-scale biogeochemical models using a grid-cell-mean WTD scheme might have underestimated the regional CH4 emissions. The spatial scale-dependent effects of WTD should be considered in future quantification of regional CH4 emissions.

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Quantifying methane point sources from fine-scale (GHGSat) satellite observations of atmospheric methane plumes

10.5194/amt-2018-171 ◽

2018 ◽

Author(s):

Daniel J. Varon ◽

Daniel J. Jacob ◽

Jason McKeever ◽

Dylan Jervis ◽

Berke O. A. Durak ◽

...

Keyword(s):

Wind Speed ◽

Methane Emissions ◽

Point Sources ◽

Small Scale ◽

Atmospheric Methane ◽

Flux Method ◽

Pixel Resolution ◽

Cross Sectional ◽

Source Rate ◽

The Cross

Abstract. Anthropogenic methane emissions originate from a large number of relatively small point sources. The planned GHGSat satellite fleet aims to quantify emissions from individual point sources by measuring methane column plumes over selected ~ 10 × 10 km2 domains with ≤ 50 × 50 m2 pixel resolution and 1–5 % measurement precision. Here we develop algorithms for retrieving point source rates from such measurements. We simulate a large ensemble of instantaneous methane column plumes at 50 × 50 m2 pixel resolution for a range of atmospheric conditions using the Weather Research and Forecasting model (WRF) in large eddy simulation (LES) mode and adding instrument noise. We show that standard methods to infer source rates by Gaussian plume inversion or source pixel mass balance are prone to large errors because the turbulence cannot be properly parameterized on the small scale of instantaneous methane plumes. The integrated mass enhancement (IME) method, which relates total plume mass to source rate, and the cross-sectional flux method, which infers source rate from fluxes across plume transects, are better adapted to the problem. We show that the IME method with local measurements of the 10-m wind speed can infer source rates with error of 0.07–0.17 t h−1 + 5–12 % depending on instrument precision (1–5 %). The cross-sectional flux method has slightly larger errors (0.07–0.26 t h−1 + 8–12 %) but a simpler physical basis. For comparison, point sources larger than 0.5 t h−1 contribute more than 75 % of methane emissions reported to the U.S. Greenhouse Gas Reporting Program. Additional error applies if local wind speed measurements are not available, and may dominate the overall error at low wind speeds. Low winds are beneficial for source detection but not for source quantification.

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Design and application of a mobile ground-based observatory for continuous measurements of atmospheric trace gas and criteria pollutant species

Atmospheric Measurement Techniques ◽

10.5194/amt-8-3481-2015 ◽

2015 ◽

Vol 8 (8) ◽

pp. 3481-3492 ◽

Cited By ~ 5

Author(s):

S. E. Bush ◽

F. M. Hopkins ◽

J. T. Randerson ◽

C.-T. Lai ◽

J. R. Ehleringer

Keyword(s):

Spatial Scales ◽

Point Sources ◽

Trace Gas ◽

Mobile Laboratory ◽

Gas Emissions ◽

Trace Gas Emissions ◽

Criteria Pollutants ◽

Position Data ◽

Health Related ◽

Atmospheric Trace Gas

Abstract. Ground-based measurements of atmospheric trace gas species and criteria pollutants are essential for understanding emissions dynamics across space and time. Gas composition in the lower 50 m of the atmosphere has the greatest direct impacts on human health as well as ecosystem processes; hence data at this level are necessary for addressing carbon-cycle- and public-health-related questions. However, such surface data are generally associated with stationary measurement towers, where spatial representation is limited due to the high cost of establishing and maintaining an extensive network of measurement stations. We describe here a compact mobile laboratory equipped to provide high-precision, high-frequency, continuous, on-road synchronous measurements of CO2, CO, CH4, H2O, NOx, O3, aerosol, meteorological, and geospatial position data. The mobile laboratory has been deployed across the western USA. In addition to describing the vehicle and its capacity, we present data that illustrate the use of the laboratory as a powerful tool for investigating the spatial structure of urban trace gas emissions and criteria pollutants at spatial scales ranging from single streets to whole ecosystem and regional scales. We assess the magnitude of known point sources of CH4 and also identify fugitive urban CH4 emissions. We illustrate how such a mobile laboratory can be used to better understand emissions dynamics and quantify emissions ratios associated with trace gas emissions from wildfire incidents. Lastly, we discuss additional mobile laboratory applications in health and urban metabolism.

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Beneficial Reuse of Industrial CO2 Emissions Using a Microalgae Photobioreactor: Waste Heat Utilization Assessment

Energies ◽

10.3390/en12132634 ◽

2019 ◽

Vol 12 (13) ◽

pp. 2634 ◽

Cited By ~ 4

Author(s):

Daniel T. Mohler ◽

Michael H. Wilson ◽

Zhen Fan ◽

John G. Groppo ◽

Mark Crocker

Keyword(s):

Heat Transfer ◽

Power Plant ◽

Biomass Production ◽

Waste Heat ◽

Point Sources ◽

Production Costs ◽

Transfer Coefficients ◽

Wind Speeds ◽

Heat Utilization ◽

Waste Heat Utilization

Microalgae are a potential means of recycling CO2 from industrial point sources. With this in mind, a novel photobioreactor (PBR) was designed and deployed at a coal-fired power plant. To ascertain the feasibility of using waste heat from the power plant to heat algae cultures during cold periods, two heat transfer models were constructed to quantify PBR cooling times. The first, which was based on tabulated data, material properties and the physical orientation of the PBR tubes, yielded a range of heat transfer coefficients of 19–64 W m−2 K−1 for the PBR at wind speeds of 1–10 m s−1. The second model was based on data collected from the PBR and gave an overall heat transfer coefficient of 24.8 W m−2 K−1. Energy penalties associated with waste heat utilization were found to incur an 18%–103% increase in energy consumption, resulting in a 22%–70% reduction in CO2 capture for the scenarios considered. A techno-economic analysis showed that the cost of heat integration equipment increased capital expenditures (CAPEX) by a factor of nine and increased biomass production costs by a factor of three. Although the scenario is thermodynamically feasible, the increase in CAPEX incurs an increase in biomass production cost that is economically untenable.

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A quantum cascade laser absorption spectrometer devoted to the in situ measurement of atmospheric N2O and CH4 emission fluxes

Review of Scientific Instruments ◽

10.1063/1.4790376 ◽

2013 ◽

Vol 84 (2) ◽

pp. 023103 ◽

Cited By ~ 17

Author(s):

I. Mappé ◽

L. Joly ◽

G. Durry ◽

X. Thomas ◽

T. Decarpenterie ◽

...

Keyword(s):

Quantum Cascade Laser ◽

In Situ Measurement ◽

Ch4 Emission ◽

Quantum Cascade ◽

Laser Absorption ◽

Emission Fluxes ◽

Absorption Spectrometer

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Design and application of a mobile ground-based observatory for continuous measurements of atmospheric trace-gas and criteria pollutant species

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-33-2015 ◽

2015 ◽

Vol 8 (1) ◽

pp. 33-63 ◽

Cited By ~ 1

Author(s):

S. E. Bush ◽

F. M. Hopkins ◽

J. T. Randerson ◽

C.-T. Lai ◽

J. R. Ehleringer

Keyword(s):

Spatial Scales ◽

Point Sources ◽

Trace Gas ◽

Mobile Laboratory ◽

Gas Emissions ◽

Ch4 Emissions ◽

Trace Gas Emissions ◽

Criteria Pollutants ◽

Position Data ◽

Atmospheric Trace Gas

Abstract. Ground-based measurements of atmospheric trace gas species and criteria pollutants are essential for understanding emissions dynamics across space and time. Gas composition in the surface 50 m has the greatest direct impacts on human health as well as ecosystem processes, hence data at this level is necessary for addressing carbon cycle and public health related questions. However, such surface data are generally associated with stationary measurement towers, where spatial representation is limited due to the high cost of establishing and maintaining an extensive network of measurement stations. We describe here a compact mobile laboratory equipped to provide high-precision, high-frequency, continuous, on-road synchronous measurements of CO2, CO, CH4, H2O, NOx, O3, aerosol, meteorological, and geospatial position data. The mobile laboratory has been deployed across the western USA. In addition to describing the vehicle and its capacity, we present data that illustrate the use of the laboratory as a powerful tool for investigating the spatial structure of urban trace gas emissions and criteria pollutants at spatial scales ranging from single streets to whole ecosystem and regional scales. We identify fugitive urban CH4 emissions and assess the magnitude of CH4 emissions from known point sources. We illustrate how such a mobile laboratory can be used to better understand emissions dynamics and quantify emissions ratios associated with trace gas emissions from wildfire incidents. Lastly, we discuss additional mobile laboratory applications in health and urban metabolism.

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Potential of next-generation imaging spectrometers to detect and quantify methane point sources from space

10.5194/amt-2019-202 ◽

2019 ◽

Author(s):

Daniel H. Cusworth ◽

Daniel J. Jacob ◽

Daniel J. Varon ◽

Christopher Chan Miller ◽

Xiong Liu ◽

...

Keyword(s):

Spectral Resolution ◽

Signal To Noise Ratio ◽

Optimal Estimation ◽

Estimation Algorithm ◽

Global Scale ◽

Point Sources ◽

Emission Rates ◽

Atmospheric Methane ◽

Pixel Resolution ◽

Gas Fields

Abstract. We examine the potential for global detection of methane plumes from individual point sources with the new generation of spaceborne imaging spectrometers (EnMAP, PRISMA, EMIT, SBG) scheduled for launch in 2019–2025. These instruments are designed to map the Earth's surface with a sampling distance as fine as 30 × 30 m2 but they have spectral resolution of 7–10 nm in the 2200–2400 nm band that should also allow useful detection of atmospheric methane. We simulate scenes viewed by EnMAP (10 nm spectral resolution, 180 signal-to-noise ratio) using the EnMAP End-to-End Simulation Tool with superimposed methane plumes generated by large-eddy simulations. We retrieve atmospheric methane and surface reflectivity for these scenes using the IMAP-DOAS optimal estimation algorithm. We find an EnMAP precision of 4–13 % for atmospheric methane depending on surface type, allowing effective single-pass detection of 100+ kg h−1 methane point sources depending on surface brightness, surface homogeneity, and wind speed. Successful retrievals over very heterogeneous surfaces such as an urban mosaic require finer spectral resolution. We simulated the EnMAP capability with actual plume observations over oil/gas fields in California from the airborne AVIRIS-NG sensor (3 × 3 m2 pixel resolution, 5 nm spectral resolution, SNR 200–400). We spectrally and spatially downsampled AVIRIS-NG images to match EnMAP instrument specifications and found that we could successfully detect point sources of ~ 100 kg h−1 over bright surfaces. Estimated emission rates inferred with a generic Integrated Mass Enhancement (IME) method agreed within a factor of 2 between EnMAP and AVIRIS-NG. Better agreement may be achieved with a more customized IME method. Our results suggest that imaging spectrometers in space could play a transformative role in the future for quantifying methane emissions from point sources on a global scale.

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Detecting high-emitting methane sources in oil/gas fields using satellite observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-16885-2018 ◽

2018 ◽

Vol 18 (23) ◽

pp. 16885-16896 ◽

Cited By ~ 10

Author(s):

Daniel H. Cusworth ◽

Daniel J. Jacob ◽

Jian-Xiong Sheng ◽

Joshua Benmergui ◽

Alexander J. Turner ◽

...

Keyword(s):

Return Time ◽

Low Earth Orbit ◽

Point Sources ◽

High Mode ◽

Observation System ◽

Large Contribution ◽

Atmospheric Methane ◽

Gas Field ◽

Gas Fields ◽

Oil Gas

Abstract. Methane emissions from oil/gas fields originate from a large number of relatively small and densely clustered point sources. A small fraction of high-mode emitters can make a large contribution to the total methane emission. Here we conduct observation system simulation experiments (OSSEs) to examine the potential of recently launched or planned satellites to detect and locate these high-mode emitters through measurements of atmospheric methane columns. We simulate atmospheric methane over a generic oil/gas field (20–500 production sites of different size categories in a 50×50 km2 domain) for a 1-week period using the WRF-STILT meteorological model with 1.3×1.3 km2 horizontal resolution. The simulations consider many random realizations for the occurrence and distribution of high-mode emitters in the field by sampling bimodal probability density functions (PDFs) of emissions from individual sites. The atmospheric methane fields for each realization are observed virtually with different satellite and surface observing configurations. Column methane enhancements observed from satellites are small relative to instrument precision, even for high-mode emitters, so an inverse analysis is necessary. We compare L1 and L2 regularizations and show that L1 regularization effectively provides sparse solutions for a bimodally distributed variable and enables the retrieval of high-mode emitters. We find that the recently launched TROPOMI instrument (low Earth orbit, 7×7 km2 nadir pixels, daily return time) and the planned GeoCARB instrument (geostationary orbit, 2.7×3.0 km2 pixels, 2 times or 4 times per day return times) are successful (> 80 % detection rate, < 20 % false alarm rate) at locating high-emitting sources for fields of 20–50 emitters within the 50×50 km2 domain as long as skies are clear. They are unsuccessful for denser fields. GeoCARB does not benefit significantly from more frequent observations (4 times per day vs. 2 times per day) because of a temporal error correlation in the inversion, unless under partly cloudy conditions where more frequent observation increases the probability of clear sky. It becomes marginally successful when allowing a 5 km error tolerance for localization. A next-generation geostationary satellite instrument with 1.3×1.3 km2 pixels, hourly return time, and 1 ppb precision can successfully detect and locate the high-mode emitters for a dense field with up to 500 sites in the 50×50 km2 domain. The capabilities of TROPOMI and GeoCARB can be usefully augmented with a surface air observation network of 5–20 sites, and in turn the satellite instruments increase the detection capability that can be achieved from the surface sites alone.

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Towards accurate methane point-source quantification from high-resolution 2-D plume imagery

Atmospheric Measurement Techniques ◽

10.5194/amt-12-6667-2019 ◽

2019 ◽

Vol 12 (12) ◽

pp. 6667-6681 ◽

Cited By ~ 3

Author(s):

Siraput Jongaramrungruang ◽

Christian Frankenberg ◽

Georgios Matheou ◽

Andrew K. Thorpe ◽

David R. Thompson ◽

...

Keyword(s):

Wind Speed ◽

Infrared Imaging ◽

Methane Flux ◽

Point Sources ◽

Emission Rates ◽

Flux Rate ◽

Background Wind ◽

Imaging Spectrometer ◽

Wind Speeds ◽

Methane Enhancement

Abstract. Methane is the second most important anthropogenic greenhouse gas in the Earth climate system but emission quantification of localized point sources has been proven challenging, resulting in ambiguous regional budgets and source category distributions. Although recent advancements in airborne remote sensing instruments enable retrievals of methane enhancements at an unprecedented resolution of 1–5 m at regional scales, emission quantification of individual sources can be limited by the lack of knowledge of local wind speed. Here, we developed an algorithm that can estimate flux rates solely from mapped methane plumes, avoiding the need for ancillary information on wind speed. The algorithm was trained on synthetic measurements using large eddy simulations under a range of background wind speeds of 1–10 m s−1 and source emission rates ranging from 10 to 1000 kg h−1. The surrogate measurements mimic plume mapping performed by the next-generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) and provide an ensemble of 2-D snapshots of column methane enhancements at 5 m spatial resolution. We make use of the integrated total methane enhancement in each plume, denoted as integrated methane enhancement (IME), and investigate how this IME relates to the actual methane flux rate. Our analysis shows that the IME corresponds to the flux rate nonlinearly and is strongly dependent on the background wind speed over the plume. We demonstrate that the plume width, defined based on the plume angular distribution around its main axis, provides information on the associated background wind speed. This allows us to invert source flux rate based solely on the IME and the plume shape itself. On average, the error estimate based on randomly generated plumes is approximately 30 % for an individual estimate and less than 10 % for an aggregation of 30 plumes. A validation against a natural gas controlled-release experiment agrees to within 32 %, supporting the basis for the applicability of this technique to quantifying point sources over large geographical areas in airborne field campaigns and future space-based observations.

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Using a new divergence method to quantify methane emissions with TROPOMI on Sentinel-5p

10.5194/egusphere-egu21-12565 ◽

2021 ◽

Author(s):

Mengyao Liu ◽

Ronald Van der A ◽

Michiel Van Weele ◽

Henk Eskes ◽

Xiao Lu ◽

...

Keyword(s):

Large Scale ◽

A Priori ◽

The United States ◽

Global Scale ◽

Methane Emissions ◽

Atmospheric Methane ◽

Permian Basin ◽

Wind Speeds ◽

Gas Fields ◽

Oil Gas

The high-resolution Tropospheric Monitoring Instrument (TROPOMI) satellite observations of atmospheric methane offer a powerful tool to identify emission hot spots and quantify regional emissions. The divergence of horizontal fluxes of NO2 has already been proven to be an efficient way to resolve and quantify high sources on a global scale. Since the lifetime of CH4 is in the order of 10 years, the sinks can be ignored at the synoptic time scale which makes the divergence method even more applicable to CH4 than to short-lived NO2.&#160; Because plumes of newly emitted CH4 disperse within the Planetary Boundary Layer (PBL), we first convert the satellite observed total column average (XCH4) to a regional enhancement of methane in the PBL (&#8710;XCH4_PBL) by using the CAMS global methane background reanalysis fields above the PBL. These model fields represent the transport- and chemically-modulated large-scale distribution of methane. Secondly, the divergence of &#8710;XCH4_PBL is derived by the use of the wind speeds halfway within the PBL. Based on the divergence, methane emissions are estimated on a 0.25&#176;&#215; 0.25&#176; grid. We tested our new method for Texas in the United States and quantified methane emissions from the well-known oil-gas fields in the Permian Basin, as well as from &#8211; less well quantitatively established &#8211; oil-gas fields located in southern coastal areas.&#160; Compared to traditional inverse methods, our method is not restricted by an a priori emission inventory and so far unidentified local sources (i.e. emissions from livestock in feed yards) may be found. Due to its computational efficiency, the method might be applied in the near future globally on the current spatial resolution.

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