In the company of gods under the heavens

My time at NOAA is almost at an end, and I’ve mostly harked on about the work of monitoring the “major” greenhouse gases, paying a little lip service to what else goes on. So I’ll go a tiny way to rectifying that with a post about another piece of analysis that takes place. Some ozone depleting gases are also greenhouse gases. Did you know that? So monitoring of those gases aren’t just important to see if we are being successful in tackling the ‘ozone hole’, they also need to be kept an eye on with regards to global warming. And this beauty of a machine is used in the analysis of this task:

The “Pre-concentration of Environmentally Relevant Species” (or PERSeus) is a hybrid machine of commercial and bespoke parts. Let’s just say it is a very clever piece of machinery!

I love how researchers find way of coming up with acronyms for research projects, pieces of equipment or organisations. To give the machine pictured above the name “PERSEUS” based on the function it performs and how it does it needs a little bit of imagination. When Ben Miller and his colleagues came up with the concept of this machine, well, let’s just say imagination clearly was not in short supply!

Before I go onto the science, let’s digress a little, as you may have heard the name “Perseus” before, or a derivative of it.

Those of us who love stargazing and are lucky enough to get a very clear starry sky (the best I’ve ever seen was in the mountains of Wales when I was about 12 years old, but my in-laws family house outside of Bozeman, Montana sports equally amazing stellar views) would have heard of the Perseid meteor shower. They are named as such because they appear to come from the northern hemisphere constellation of Perseus.

Credit: NASA/JPL

They are pretty reliable too, as the earth goes through a debris cloud from a comet every August as it orbits the sun. I’ve nicked named them the ‘summer holiday’ meteor shower, since it’s always the summer break off school when they are in the sky.


So who was Perseus? That I didn’t know until I looked it up. In Greek mythology he was a son of Zeus and a hero before Hercules came along. He was also the guy who slayed Medusa. (Anyone else see the comic irony of him being idolised as a statue with Medusa’s head!?). There seems to be no link between the myth of Perseus and the name given to the machine other than the acronym. I didn’t really think to ask Ben Miller at the time – opportunity missed!

Ben wrote a very good piece about PERSEUS in a recent edition of an internal newsletter. It does a good job explaining what it does. So here it is in full:

PERSEUS turns three years old! – Ben Miller (GMD internal newsletter – October 2017)
October 2017 marks the third year of ‘operational mode’ for ‘PERSEUS’, the latest gas chromatography / mass spectrometry (GC/MS) instrument developed in GMD. The results to date are a dataset of 60 CFCs, HCFCs, HFCs, PFCs, chlorinated solvents, hydrocarbons and sulfur-containing compounds from analysis of over 27,000 flasks collected over North America as part of GGGRN’s (Global Greenhouse Gas Global Network’s) tall tower and small aircraft network. With mole fractions of these atmospheric ultra-trace gases often spanning ranges over 2 ppb (e.g., ethane) down to 200 ppq (e.g., HFC-236fa), PERSEUS is unique amongst its kind in being able to characterize and correct for instrument nonlinearities over the wide dynamic ranges of these analytes. The resulting time series reveal the atmospheric behavior of each species, with some exhibiting seasonality, while others are characterized by atmospheric lifetimes ranging from days to 1000’s of years. With many of these species implicated in ozone depletion, radiative forcing and/or air quality issues, and with diverse sources that can include natural as well as anthropogenic origins, each species has a unique story to tell. These data may be viewed via the InterActive Data Visualization tool (iadv) at .

For the analysis process, first discarded are all the gases in an air sample that will not be to analysed, that’s everything from the major gases (oxygen, nitrogen etc) down to the trace gases (carbon dioxide, methane etc). Here we’re only interested in gases which have concentrations of ppt (parts-per-trillion) or lower! In fact, the concentations are so small, they don’t even appear on the ‘trace gases’ pie chart of this diagram.


PERSEUS capture these gases this by pushing the air sample through an exceptionally cold chamber, and the remaining gas that sticks behind is collected in a very thin hollow coil. The clever part is that the gases (CFCs, HFCs etc) all flow through this hollow coil at different rates. Ben used the analogy of particles in a river: the smaller, lighter particles (analogous to e.g. sulfur hexafloride (SF6)) will follow down the river quicker, therefore will appear on the analyser first. Other particles are like the heavy rocks that roll along the river bed and will appear last like Bromoform (CHBr3). This produces a spectogram:

Many halocarbons are a human construct, the most famous being CFCs. However, a number of them are produced naturally. Bromofrom (CHBr3) is produced by seaweeds and phytoplankton. Methyl chloride (CH3Cl) and methyl bromide (CH3Br) are produced by plants which found in coastal environments (such as salt-marshes) as a way of ‘de-stressing’ from saltwater intake. Think of that the next time you visit the marshes on the North Norfolk coast!

So what’s the current situation with halocarbons and in particular the ‘hole’ in the ozone? Well, the news is good regarding the infamous CFCs according the to analyses here at NOAA Boulder:


CFC-12 isn’t decreasing as quickly as plenty of people are still using old refrigerators (they built them to last in the ol’ days, didn’t they!?).  CFCs were used as the refrigerant gas and these old appliances are either slowly leaking through age or are not being disposed of properly, allowing the gas to simply exhaust to the atmosphere. However, you can clearly see that the Montreal Protocol had an almost instant impact.

The use of replacements for CFCs etc are on the increase. And while they don’t live in the atmosphere as long, they still can destroy ozone if they get up into the stratosphere. Clearly us humans have a habit of creating another problem through solving one…


What’s the prognosis for the ozone hole? Cue cool graphics from NASA:

So while the ‘real’ Perseus went around cutting off monsters heads, mechanical PERSEUS will instead quietly go about the equally important business of continuing to keep a watchful eye on halocarbons: the gases banned by the Montreal Protocol, their replacements and any natural sources to see singles of chances in the biosphere.


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