Mobile, In Situ Surface Greenhouse Gas Validation of Satellite Greenhouse Gas Anomalies - Fossil Fuel Industrial Contributions

Methane's (CH4) large global warming potential and likely increasing future emissions due to global warming feedbacks emphasize its importance to anthropogenic greenhouse warming. Furthermore, CH4 regulation has a far higher potential for near-term climate change mitigation versus carbon dioxide CO2, the other major anthropogenic GreenHouse Gas (GHG). Uncertainties in CH4 budgets arise from the current poor characterization of many CH4 sources - in part from a lack of sufficiently accurate assessments of the temporal and spatial emissions and controlling factors of highly variable anthropogenic and natural CH4 surface fluxes and the lack of global-scale (satellite) data at sufficiently high spatial resolution to resolve sources.

Mobile surface in situ trace gas air quality measurements have a long tradition; however, numerous challenges (vibration, electrical noise, data connectivity, etc.) have created a predisposition for stationary air quality measurements. Still, challenges in interpreting stationary measurements in the near field of strong dispersed and complex sources for emission strength arise from disentangling the effects of temporal variability, transport variability, and in some cases spatial emission variability. Snapshot data allows detangling these three factors, and can be provided by fast in situ systems (airborne or surface at highway speed), or airborne imaging spectroscopy systems.

Two platform/instrumentation suites were pioneered to address mobile measurement challenges highlighted in a 2010 transcontinental survey, which used a gas chromatograph. Key was the addition of real-time concentration data monitoring, which was applied in 2012 in S. California with a cavity ring down spectrometer. However, this information was inadequate for effective survey data collection – currently, realtime data visualization and integration in the GoogleEarth mapping environment, including winds, are implemented to allow adaptive survey route planning in the wind frame of reference.

AMOG (AutoMObile Greenhouse gas) Surveyor is an innocuous, commuter car (Nissan Versa) with a trunk science package including an Inverter/Charger, solar batteries, cavity ringdown spectrometer (Fast GHG Sensor, Los Gatos Research (LGR)), high flow scroll vacuum pump, ultrasonic anemometer/weather station, GPS, incident radiation, thermal radiometer, solar spectrometer, continuous video recording (aiding post-processing interpretation), and high speed internal network. The trunk package reduces noise to tolerable levels, allowing collection of extensive (>160 km/day) and long-term data on GHG sources and transport processes while commuting. Custom software provides realtime data integration and visualization in GoogleEarth. Network-push allows remote, realtime survey participation and data processing.

MACLab (Mobile Atmospheric Composition Laboratory) is a 12-ton, 37' diesel RV toyhauler, whose garage was converted for air chemistry analysis, including 4 gas chromatographs (SRI GC) on an independent air suspension rack, ultrapure air and hydrogen generators, 8.5 kw generator, 18-m pneumatic mast, greenhouse gas cavity ringdown spectrometer, high flow vacuum lines, meteorology station, 3D sonic anemometer, continuous video scene recording, and internal network allowing all MACLab computers to access all instruments/video streams. The habitation module supports to a 4-person team, allowing round-the-clock data collection without regards to proximity to hotels, restaurants, and bathrooms, allowing extended mobile air quality measurement.

MACLab gas chromatographs currently are configured to measure C2-C6+, alkanes, alkenes, alkynes, and BTEX on a ~20 min cycle, NOx, and other gases. Multiple gases and parameter measurements are used to de-convolve distinct sources. When stationary, the mast is raised to measure winds and to collect air above the near-surface layer, eliminating exhaust contamination. Efforts are underway to resolve issues in MACLab real-time wind data; during a transcontinental, 18,000+ km survey, summer 2013, MACLab paused every 1-3 hours to measure winds.

These platforms support the NASA HyspIRI and the joint NASA -ESE COMEX–CO2 Methane EXperiment campaigns, providing surface ground-reference data to validate remote-sensing derived GHG source strength through inversion modeling. In the HyspIRI campaign, the AVIRIS, Airborne Visible Infrared Imaging Spectrometer - a HyperSpectral Imaging (HSI) sensor - will collect snapshot Short Wave InfraRed (SWIR) data on a range of important GHG sources in Southern California including natural geology (La Brea, Coal Oil Point), fossil fuel production (Bakersfield), and refining (El Segundo, Oakland), husbandry, and megacity. COMEX supports the NASAs HyspIRI and ESAs CarbonSAT satellite developments by collecting contemporaneous, comparatively high spectral resolution GHG remote sensing data (MAMAP, University of Bremen and GFZ) , contemporaneous Thermal InfraRed (TIR) HSI data (Mako, Aerospace Corp.), in situ airborne GHG and atmospheric characterization (Picarro, NASA Ames and CIRPAS aircraft instrument suite) with the Navy CIRPAS plane, and additional in situ GHG data from the NASA Ames Picarro aboard the AlphaJet.

The airborne COMEX and HyspIRI campaigns support future satellite missions, like CarbonSat (ESA) and HyspIRI (NASA) by extending remote sensing data to top of atmosphere. Specifically, MACLab continental-scale data is compared with satellite GHG data (GOSAT and SCIAMACHY-historical) to ground reference regional scale GHG trends for comparison with inventories, such as EDGAR.

Transcontinental 2013 data confirmed satellite (SCIAMACHY/GOSAT) and surface data from 2010 showing strong CH4 anomalies correlated with Fossil Fuel Industrial (FFI) activities. The new data also suggest that Great Plains satellite CH4 enhancements are related in part to local production rather than solely advection from the Gulf Coast.

Houston GHG data show the dominant CH4 and CO2 sources related to the extensive FFI facilities and activities near I-10. The Houston survey first investigated the source and vicinity, noting wind directions and speed during “wind data pauses.” Then, crosswind transects were taken (north-south) for several downwind distances. Given plume dimensions, the transect sequence took ~7 nocturnal hours to complete. Nocturnal measurements provide effective urban mobility (traffic) and decreased (road-biased) vehicular emissions compared to daytime surveys.

Surveys near and within refineries showed strong transient CH4 sources clearly related to specific refining structures. Spatial correlation between CH4 and CO2 were close but often offset, indicating distinct origins. Interestingly, the highest CH4 concentrations were not in the immediate vicinity of the refineries, but downwind in the vicinity of the city center during a north-south transect, where levels to 10 ppm were observed, higher than observed during 2010 Houston surveys. Inversion plume modeling (7) of transect data can then estimate source strengths.