The Instrument

I can't believe it's been three days since my last post! Time is certainly flying up here; we only have 8ish days left of sampling and I only have 10 1/2 more days at Summit. That means that I have been at Summit for just about 11 days.

I'm not quite sure how I avoided talking about the instrument we're running up for those 11 days but I managed to do so somehow. Let's remedy that tonight. I have mentioned the mist chamber ion chromatograph (MC-IC) in passing but haven't really gone over how it works.

The MC-IC is housed in the Bally building along with a few instruments from Georgia Tech. Here's a view outside and inside. Our MC-IC is the grey box in the bottom left of the inside picture. This grey casing is responsible for the MC-IC (uncreative) nickname: grey box.




The MC-IC is responsible for the collection and analysis of atmospheric samples, more specifically, atmospheric soluble (dissolves easily in water) acidic gases. For this particular project, we're interested in measurement of nitric acid (HNO3) and nitrous acid (HONO) as these species are more closely related to the snow photochemistry we're trying to understand. We're also interested in measuring the halogen, bromine (Br), as we hypothesize it may be a large player in the mismatch between modeled processes (those we determine using equations and formulas we know from theory) in the snow and processes that are measured. Fortunately, the MC-IC measures all three species (as well as a couple of others) simultaneously making it a very useful instrument.

Air is drawn in through the inlet shown below by a vacuum pump housed in the Bally building.



The inlet is capped with a filter (contained in the yellow-ish filter holder at the end of the tube) to keep particles and snow from contaminating our measurements of the gases. The long tub leads into the Bally building where it connects to the instrument. This part of the inlet is heated so that 1) the sample stays warm and 2) substances like HNO3 that like to stick to surfaces, do not.

Once inside both the building and the instrument, the air is sucked into two glass chambers filled with water ultimately creating a mist. Below is a shot of the mist chambers in action.


Capping the mist chambers are two head filters held in place by white filter holders (see photo below). These prevent the mist from entering the vacuum lines (the two black tubes connected to the filter holders) and the pump. These have to be changed daily to avoid leaks in the filters.

Samples are misted for 27 minutes--a much longer sampling time than for a dirty site, such as Houston, TX (where I was with the mist chamber, there, misting was only for 5 minutes). Why? Concentrations of our species of interest are much lower at a clean place like Summit so we have to sample for a longer period of time to get concentrations in a range that is measurable by IC.

Once the 27 minutes is up, samples are drawn from the mist chambers into the syringes in the picture above (glass tubes towards the bottom). From there, the two samples take different paths. Samples on the left take the "traditional" MC-IC route and are injected into the IC. With the help of a carrier solution (called "eluent"), ions are separated by charge and detected in the IC. The product is a curve of signal, shaped like a bell, who's area underneath gives information about concentration of our favorite acidic gases. The other syringe associated with the right mist chamber does not inject sample into the IC but rather into a brown bottle houses at the bottom of the instrument. These are samples that will be examined for the isotopes of oxygen and nitrogen. What is an isotope you may wonder? Think of oxygen (or nitrogen) like ice cream. Just like chocolate and vanilla are different flavors of ice cream, isotopes are different "flavors" of an element. Isotopes can tell us a whole lot about the source of the soluble gases we're interested in and thus are very useful. These samples have yet to be analyzed and won't be until after we get back. This is Dorothy's project. I'm curious to see the results!

And that's pretty much it. When it's behaving, which fortunately it has been (knock on wood!), it's a very easy instrument to run. The biggest production with it is a recalibration every time new eluent is made (~every 5 days) and even that isn't terribly complex. Tedious maybe, but not hard. My kind of instrument!

On a completely different note, Happy Flag Day! I must admit I would have had absolutely no idea that today is flag day were it not for Ken, the Camp Manager, announcing the holiday at the 8am daily meeting. What a horrible American I am. In honor of the day, the camp flags were flyin' high in the front of the big house.


On the left is the Danish flag, on the right, the Greenlandic flag, and the middle, well if you don't know it, you're a worse American than me!