A Closer Look at Tracking Fracking Emissions

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Lee Harrison, a senior research associate at the Atmospheric Sciences Research Center of SUNY Albany, sent this comment as part of an exchange following this recent post on Dot Earth: “Can Public Leak Patrols Stem Gas Emissions at a Profit?” Link: http://nyti.ms/TI96uv

The post explored how infrared imagery might offer the public a role in tracking emissions of methane and other gases from gas and oil facilities. The comment is posted in full here because of the space constraints in the comment section of the blog.

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A Closer Look at Tracking Fracking Emissions

  1. 1. Lee Harrison, a senior research associate at the Atmospheric Sciences Research Centerof SUNY Albany, sent this comment as part of an exchange following this recent post onDot Earth: “Can Public Leak Patrols Stem Gas Emissions at a Profit?”The post explored how infrared imagery might offer the public a role in trackingemissions of methane and other gases from gas and oil facilities. The comment is postedin full here because of the space constraints in the comment section of the blog.From Lee Harrison:Andy -- this isnt any sort of grudge match on my part, nor I assume on yours. However Ithink there is a pretty serious list of issues to discuss and get right here:First, a significant part of whatever issue is before us is about the word "detect" ... and itis on that score that I have a pretty serious problem as a scientist in my field with what"somebody" is claiming here; at best this is an extremely "non-specific indicator," not adetector. Indications ("signs" in medical parlance) have great utility in diagnostic workof any kind, but they dont represent scientific or legal "detection."A second issue of practical importance here is the distinction between "Thermal Imaging"and "IR camera." These are not the same thing at all. I will return to some details of thisbelow ... but had your article talked about citizens with "thermal imagers" I would nothave been so immediately critical in terms of physics of detection ... but would havequickly remarked that few citizens have decent thermal imagers, they are expensive(though the technologies are getting better).Ill discuss these in backward order:*****With regard to "Thermal Imaging" please note that the patent you cite, Benson et al.US2008/0231719 states (capitalizations other than acronyms are mine for emphasis):"the focal plane array comprises a COOLED two-dimensonal array of quantum-wellinfrared photodetectors (QWIP) having a peak responsivity in the wavelength range 10.4to 10.8 micrometers. The camera has a COOLED band pass optical filter having a peaktransmittance approximately centered at 10.57 micrometers and a full width halfmaximum spectral transmittance bandwidth of approximately 10.3 to 10.7micrometers. ..."much later in the document at [0010] it states "the example thermography cameras eachinclude a cyrocooler refrigeration device or container of liquid nitrogen, for cooling thefocal plane array and the optical filter (cold filter) to 77 to 100 Kelvin duringoperation ...."Joe Average sure as heck does not have or operate one of these, and they are not a simple"IR camera." Ill discuss the significance of lines [0011] and [0012] below, about lower- 1
  2. 2. cost systems operating at more reasonable temperatures, but before going onto that pleasenote that the fact that a patent has been granted is not proof that something works,certainly not any statement of how well it works. This patent claims a physicalembodiment and "a use."Low performance thermal imaging systems in the 10 micron domain (the maximum ofthe Planck function at reasonable ambient temperatures, and also by quantum-mechanicalcircumstance a "window region" for CO2 and relatively low H2O absorption ... which iswhy this window is so important to climate) are getting "reasonably cheap" .... see e.g.http://www.opticsplanet.com/flir-scout-ps-24-thermal-vision-digital-camera.html?gclid=CJmeksjX2LMCFYuZ4AodDRMAWg&ef_id=UFza4wAADivJ5mXu:20121118140401:sBut this device, which is good enough to see hot bodies at night, is not likely to have thesensitivity or the dynamic range to do the differential absorption problem, particularlyduring the day.*****There is also the problem/issue of the intended use of this detection legally. If the goal isto actually make a citizens army of leak detectors self funding via a bounty mechanism,the method of detection must pass the legal standard for "preponderance of evidence." Inthis regard there is a large body of legal history and precedent about specificity (lack ofinterferences) for forensic methods ... for very good reason. I strongly doubt that anyonecould claim such a bounty on the basis of an IR camera photograph alone.As a practical matter I think the attraction of the IR camera in this application is that onecan see something without having access; no trespass is intrinsically necessary. Howeverthe law on IR camera and Thermal Imaging doesnt favor warrantless use: see Kyllo vsUS, 2001 andhttp://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&vol=000&invol=99-8508One always wants to double-check anything you find in Wikipedia (I havent!) but itsarticle on this is "a first indication" of interpretation and suggests that there has not beena major change in court position since Kyllo vs US.http://en.wikipedia.org/wiki/Kyllo_v._United_StatesNow, going back to the physics and fundamentals of the issues here ... which was, andremains, my principal objection here:That "EPA background sheet" you provide me doesnt have ANY description of theactual physics of the detection or discussion of interferences .. none. It contains no 2
  3. 3. references to reviewed work which demonstrate the claims. It simply asserts "a variety ofcomponents including methane .... pentane (the alkanes in increasing carbon order to 5)can be detected by an IR camera."Offering me a document which simply repeats the claim and nothing more isembarrassingly circular, other than it attempts to argue from the authority of "the EPA."But I see no signature, nobody taking responsibility for this at all. Im not accusing youof dummying this up ... but its ridiculous to bring something like this to a discussion as"evidence" ... whether that discussion is being conducted by scientific, legal, orjournalism standards of evidence.Going back to the Benson patent -- look at lines [0011, 0012]. These lines claim that farsimpler IR systems operating in the 3.0 - 5.0 micron domain are "suitable for detectingmethane and other hydrocarbons" ... no other proof or reference is supplied, nor is anyrequired for this patent, which is not about that.***OK, lets talk about some real physics here. Casting around the web for a convenientgraph of the absorption spectrum of Methane I came across this:http://icb.u-bourgogne.fr/omr/SMA/methane/from the Molecular Spectroscopy and Applications (Department of Optics and MatterRadiation Interactions), Institut Carnot de Bourgogne. The spectroscopy is wellexplained and there is a nice graph of the low-pressure absorption spectrum of methane.The unit of "wavenumber" may not be familiar to you, its effectively a unit of opticalfrequency, but has the curious dimension of inverse centimeters. Its a spectroscopistsconvenience to avoid very big numbers for frequencies of optical wavelengths. Wavelength = speed of light / frequency ... and the speed of light being very large.1000 wavenumbers = 10 micron wavelength10000 wavenumber = 1 micron wavelengthThe abscissa of this graph is inverse to wavelength. And what you see is four Methaneabsorption bands, the leftmost one on this graph is at wavelengths just below 10 microns,and the rightmost one is at wavelengths around 1.6 microns.Ok, on the face of it ... the band(s) to the right are "good" for cheap camera detection.This is why all of these folks are claiming "detection detection detection"And if one had a spectrometer capable of the resolution shown AND the earthsatmosphere was at 1 Torr pressure (1/760 th of sea level) then one could see a spectralfingerprint like this ... and presentation of such data would lead almost any scientist or 3
  4. 4. forensic witness would accept "yep, thats methane."But heres the big problem -- the earths atmosphere isnt 1 Torr, and there is quantum-mechanical pressure broadening, aka Lorenz broadening. And the data shown here withlarge opacities is taken over a pathlength of 100 m of pure methane at that pressure, and atemperature well below ambient anywhere except the earths poles (there is alsotemperature broadening, less important here though). These data are looking through alot of methane. You wont get columns of that much methane unless the leaking tank ispressurized and spewing a huge plume of methane (in which case OMFG is it a firehazard, huge one)Under real atmospheric conditions the spectrum is "smeared" by the pressure broadening. Thats "ok"as far as a broad spectral "camera" is concerned, but the consequence is thatthe camera doesnt see very much contrast ... precisely because it has a heck of a largeoptical bandpass. And in that bandpass there can be all sorts of other absorbers ... startingwith H2O, which has good absorption bands in these domain(s).So what is going on is that these folks are taking images, seeing something wispy orcontrasty, and arguing "it must be a methane leak." Possibly so, but jeez, a great manypossibilities that there is not. And "image interpretation" is not something with a goodhistory of evidence period.If the claim is that this is suggestive of a leak, or might be an "indicator" of a leak...grudgingly maybe ... but theres no way I can see that any court would accept thismeasurement forensically, even under "preponderance of evidence," given a half-waycompetent defense. And under Kryllo the evidence likely wouldnt be admissibleanyway. Perhaps your argument is that that a court might accept this as "probable cause"... for a REAL search warrant /measurement? Im not a lawyer, wouldnt argue that one,but again Kryllo comes into play. (And "corporations are people too, my friend.")On the otherhand if the evidence is "I marched up to the tank, lit a match ... andWHOOSH!" Not so much argument, eh? That requires trespass ... and has otherconsequences though.And finally, back to the point I started with -- why bother with the IR camera, with all ofits interferences and poor sensitivity and specificity for the job? There are many waysto measure Methane, relatively cheap laser-diode absorption cell devices do it using theabsorption lines shown and are quantitative and specific, and very sensitive. Presumingone can go downwind of the tank without trespass, or even fly through the downwindplume ... bingo. And there are no trespass arguments wrt the aircraft measurement,although there are FAA restrictions on low flight in densely populated areas. 4

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