Delta Ray Road Trip: Measuring δ13C, δ18O and concentration of CO2 across Canada Hansjurg Jost1, Peter Stow2, and Luka Mandic3 1Thermo Fisher Scientific, Reinach, Switzerland, 2ISOMASS Scientific Inc., Calgary, Canada, 3Thermo Fisher Scientific, Bremen, Germany

Conclusion The Thermo Scientific Delta Ray IRIS integrates several complementary technologies into a complete, durable, field portable system for measuring and analyzing CO2 concentration and isotope ratios. The Universal Reference Interface (URI), feeds a mixture of standard reference gases into the Delta Ray IRIS to match the concentration of the sample under study. The system was successfully operated during a trip across Canada from coast to coast. We demonstrated the ruggedness and reliability. Episodes of increased CO2 concentration were attributed to human breath and combustion sources.

Acknowledgements We would like to thank the following individuals for their support of the Delta Ray Roadtrip: Magda Mandic (Delta Ray application engineer), Luka Mandic (data analysis and web site integration) based in Bremen, Germany; the social media team of Sonya Pella with Avon Datt, Steve Day, Richard Williams based in San Jose, California and the Isomass team with Tony Cade (integration, demos, tour planning and driving), Alyisha Thomson (installation and driving), and Dave Ashwell (driving) based in Calgary. And of course all the additional drivers Nik Binder, Bryan Beattie, and Elizabeth Stow.

Overview Purpose: The Delta Ray Road Trip was conceived to demonstrate that there is now an instrument capable of being taken to the sample collection point and in fact taken to the samples along an 8000 km route across Canada.

Methods: Dive a Thermo Scientific™ Delta Ray™ Isotope Ratio Infrared Spectrometer (IRIS) from coast to coast across the second largest country in the world. This route took the Delta Ray IRIS from a coastal environment, through forests, arable farm land, urban and industrial centres, across prairies and over mountains. The vehicle was a standard RV with as few modifications as possible.

Results: Along the way there were stops at most of the major universities in Canada as well as the AGU-GAC-MAC conference in Montreal, where indoor measurements were performed. Data was uploaded in quasi realtime to a website.

Introduction As electronics have become increasingly more power efficient and circuit design has increased in density so what once required racks of units can now be compressed to a few circuit boards. In parallel with the development of electronics and computing power there has been the development of technologies that expand our measurement techniques. One of these technologies, the infrared spectrometer, has moved what was once a laboratory only technique into the field.

Until recently the measurement of isotope ratios required a laboratory based mass spectrometer. These instruments ionize gaseous CO2 in a vacuum to measure the relative ratios of atomic masses 44 (12C 16O16O), 45 (13C 16O16O) and 46 (12C 16O18O). From this raw measurements the ratios of 13C/12C and 18O/16O can be calculated. However there are problems; 17O is an interference in the mass 45 and 46 ion beams and must be corrected for, the system requires mechanical pumps to obtain the required high vacuum (10-7 mbar) and high power (nominally 5 kW depending on the configuration. On the plus side these systems are flexible, taking sample gas from a wide range of sample preparation devices. These instruments are also usually capable of measuring 15N/14N, HD/H, 18O/16O directly and 34S/32S as well as isotopes in other gas species.

The laboratory nature of the mass spectrometer has, by its very nature, limited the number of samples that can be analyzed. Shipment of sample containers pose a challenge, especially if trying to complete a time series where a high degree of time resolution necessitates many samples. The logistics of sample transportation usually limit the sampling period to once a day.

Enter the laser based Isotope Ratio Infrared Spectrometers (IRIS). Small enough and light enough, < 30 kg and using less than 500 watts in power, an IRIS should be ideal to take the measurement system to the samples rather than the other way around. Also as continuous sampling systems, these instruments lend themselves to continuous monitoring of changing environments such as those found in volcanoes, growth chambers and the very atmosphere we breathe.

These systems use tuned lasers to measure the different isotopic species in the CO2 via the absorption spectrum of the molecules. Taking the measurement point to a base camp near to sample collection point is good but delivering the instrument to the samples is better. The motto now is, take home results not samples.

FIGURE 3. Figure 3 Schematic of electrical and gas setup.

FIGURE 2. Left: at the core of Delta Ray IRIS is a mid-infrared DFG laser operating at 4.3 µm. The beam interacts in the multi-pass cell with the sample gas, all built into a monolithic bloc. Right: spectra are acquired at 500 Hz and averaged for at least 1 s before the isotope ratio is determined from the shaded areas.

Results

The route shown in Figure 5 started in Halifax and went on to Montreal with stops in Fredericton and Quebec City. In Montreal we attended the AGU-GAC-MAC (American Geophysical Union-Geology Association of Canada-Mineralogy Association of Canada) meeting.

The route then continued through Ontario stopping in Ottawa, Toronto, Waterloo and Sudbury. From Sudbury the route would take us to Sault St. Marie and around Lake Superior to Thunder Bay. Leaving Ontario for Manitoba we stopped in Winnipeg and on to Saskatchewan where we stopped at both Regina and Saskatoon. Going north from Saskatoon the route took us to Lloydminster, Edmonton and down to Calgary. After a side trip to Lethbridge the route took us over the Rocky Mountains to Kelowna and then down to Vancouver.

Universal Reference Interface (URI)

A key integral feature of Delta Ray IRIS is its universal reference interface, with which fully automated referencing and calibration are implemented, which includes a linearity and a delta scale contraction calibration. Linearity calibration determines the dependence of the isotope ratios on the concentration, and the delta scale calibration determines the scale factor by analyzing two gases with different isotopic composition. A micro machined mixing and switching core (MITCH) together with a flow controller dilutes pure CO2 reference gases to match the sample concentration to minimize the effect of instrument non-linearity. It can also select between different sample gases.

The sample gas is dried in the URI to prevent matrix effects and interaction of water and CO2 (oxygen isotope exchange) with the added benefit of providing dry mole fraction concentration data.

URI provides output to drive valves, or a user provided trigger signal can initiate sample acquisition, which is used in the plant chamber application below.

Installation

The RV was equipped with an inverter to provide 110 volts a.c. however this unit did not produce a pure sine wave and the UPS we used would not recognize the incoming power as a valid source of power. The inverter we purchased did provide a sufficiently pure sine wave for the UPS to operate correctly. The inverter was place underneath a captain’s chair immediately behind the front passenger seat. The UPS provided sufficient power (16 minutes) to allow the RV to be fuelled. A procedure was developed to keep the Delta Ray IRIS running when connecting the RV’s interior power outlets to shore power or back to engine power. A schematic is shown in Figure 3.

TeamViewer is a trademark of TeamViewer GmbH. FOAMULAR CodeBord is a registered trademark of Owens Corning. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries

This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others.

Published at the European Geosciences Union, April 17-22, Vienna, Austria

PO30339

FIGURE 5: Website showing the map with the route and the stops. Visitors to site can click on segment to see data. http://www.thermofisher.com/DeltaRayRoadTrip

FIGURE 1. Linestrength of the different isotopologues of CO2 as a function of wavelength. Wavelength of different isotopologues are shifted against each other.

FIGURE 4. Top left: RV parked for demonstration. Top right: Delta Ray IRIS strapped down on bed above driver. Bottom left: operating Delta Ray IRIS from RV table, Delta Ray IRIS is on mounted over driver seat. Bottom right: sample inlet was run through a roof window.

FIGURE 6. Time series of CO2 concentration, δ18O and δ13C as acquired while driving through Canada. Gap on May 2-4 is due to setup at GAC-MAC conference.

The Delta Ray IRIS, reference gases and zero air gas tank were mounted on a wooden base, 4’ by 2’ by 3/8”, up in the child’s sleeping area of the RV. This allowed the Delta Ray IRIS and tank to be strapped down on a sufficiently large base so that there was no possibility of movement during the trip (Figure 4).

The FOAMULAR™ CodeBord™ Extruded Polystyrene Rigid Insulation (1 Inch thick), was placed between the Delta Ray IRIS and the wood board. 6 by 1” diameter, 1/8” thick, felt pads were glued to the underside of the Delta Ray IRIS base to prevent scratching the wooden base of the child’s bed. These felt pads and the foam were the only vibration isolation used between the Delta Ray IRIS and the vehicle.

As we could not make holes in the skin of the RV, a simple snorkel was constructed by passing 1/16” stainless steel tube from the inlet of the Delta Ray IRIS to the side window of the RV. This proved not to be sufficient as the input was contaminated by our breath (see Results). Taking the input tube to the roof vent proved to be better as a better seal around the input could be made. The tube was angled to face the rear of the RV, preventing ingress of water and insects as the RV was being driven. This input proved to be very robust.

Methods Instrument description

DFG Laser

A molecule of CO2 can rotate and vibrate at specific, quantized frequencies. Replacing one isotope with another e.g. a 12C with a 13C, changes the frequencies of these vibrational and rotational transitions, thereby changing the wavelengths of light the molecule absorbs (Figure 1).

In the Delta Ray IRIS a laser passes through a gas sample and onto a detector, and measures the amount of light absorbed by the sample at a given wavelength. By shifting wavelength of the light, an absorption spectrum is generated, revealing the absorption features produced by the different isotopologues of CO2 (Figure 2).

The Thermo Scientific™ Delta Ray™ IRIS used in this work is a DFG-based middle-infrared laser sensor platform. Specifically, we access the fundamental bands of CO2 at 4.3 microns to simultaneously determine both isotopologues δ18O and δ13C of carbon dioxide at atmospheric concentration.

We apply a simple, direct absorption approach that makes use of a robust multi pass cell with only 5 m path length and a cryogen free setup. The monolithic sample cell is shown in Figure 2 together with a typical spectrum acquired by the analyzer. From the shaded areas, the isotope ratios can be calculated.

12C18O16O13C16O16O

12C16O16O

A12A13A18

dete

ctor

vol

tage

1.0

1.2

1.4

1.6

approximate wavelength [µm]

CO2

4.33

To monitor the position of the Delta Ray IRIS an off the shelf GPS module was plugged into one of the Delta Ray IRIS USB ports. A WiFi transceiver was fitted to another of the Delta Ray IRIS USB ports to allow the Delta Ray IRIS to connect to the Internet via a wireless WiFi hub set up in the RV. Data from the Delta Ray IRIS and GPS could then be read by the project team in Bremen, Germany, via TeamViewer™. This allowed for the data to be posted nightly to the web site.

FIGURE 7. Left: concentration during GAC MAC meeting. Red points are used in Keeling Plot analysis. Right: Keeling plot of red points. Source CO2 isotope ratio -23.2‰.

Another large peak in CO2 levels occurred while we were parked overnight and slept inside the vehicle. In this case, the time series shows CO2 concentrations rising from 400 ppm to 1,000 ppm. The rise began shortly after we had returned from a late dinner, and continued until we awoke in the morning. The Keeling plot again shows a clear linear fit, consistent with atmospheric CO2 mixing with a single additional source. Looking at the Y-axis intercept of the Keeling plot reveals an isotope ratio matching with human breath (Figure 8).

We examined the intake of the capillary tube and discovered that the opening in the skylight was not entirely airtight. Some air from inside the RV apparently leaked out of the opening and entered the sampling tube. As we slept inside the closed vehicle, the CO2 concentration had steadily increased until we opened the doors in the morning. This prompted us to modify the inlet to be higher above the skylight, which prevented this artifact from affecting our data for the reminder of the trip.

FIGURE 8. Left: concentration increase after midnight, suspected from humans. Right: keeling plot y-axis intercept is consistent with human breath.

FIGURE 9. Left: Overnight CO2 concentration in Sudbury. Right: Y-axis intercept points to a mixture of natural gas burning and gasoline burning.

Six days after the discovery of the impact of human breathing on rise CO2, the data show another overnight CO2 peak. This was a night when the vehicle was parked unoccupied next to a motel where we were sleeping. Over the course of the night, CO2 levels steadily increased, and after sunrise they began a steady decline. The Keeling plot showed another linear trend, but this time the Y-axis intercept points to the isotope ratio of a combustion source. The isotope ratio suggested that the CO2 came from gasoline combustion, but with a substantial portion appeared to be from burning methane.