OK, so here we go again. Heading out to Elizabeth City in North Carolina. This time it is for the Instrument Integration, this follows on from the “technical recce” trip that we did a couple of weeks ago. The visit will be much less fleeting, last time was literally overnight but it we needed to actually see what we were dealing with and talk to the guys in the hangar about the technicalities of installing the instruments and we also need to ensure that the film crew have good space to film the trip. This meant quite abit of head scratching since the director wants good ‘long shots’ and the interior isn’t exactly huge. In the end we got a plan sorted out, thankfully the crew are quite flexible and seats can be removed for some days of flying which means more room in the cabin.
After an overnight stop in Norfolk, it is a short drive down to the hangar where we will be doing the work. I’ll rendezvous with Greg from DMT and get started on the job ahead. The instrument rack is due to arrive from Boulder by lunchtime and we’ll manoeuvre it in to position in the cabin.
THE INSTRUMENTS THEMSELVES……
The instruments that we are installing will take feeds from a number of inlets which we will also fit to the aircraft. Aerosols need much more specialised plumbing (‘plumbing’ rather undersells the complexity, but you get the drift) to ensure the we are accessing a representative air sample from outside of the cabin. Aerosol inlets need to have smooth bend in the pipework systems which deliver the air to the instruments. In lay terms we want the particles to flow straight down the pipes and bends can mean that we might loose some of the larger aerosols. When teaching about this I liken it to a flowing river, sediment and debris will travel down the river but if a sharp bend is encountered some of the larger suspended material might get deposited on the river banks. You might even remember your school geography lessons about the formation of ‘ox-bow‘ lakes.
To keep the flow in the pipe the same speed as outside (as we fly along) we use pumps to control the flow rate Doing this will minimise the likelihood of aerosol particles being lost on the tube walls. The technical term for this loss is ‘impacted’. In fact with abit of thought we can remove large particles using impaction by designing an appropriate dimensioned chamber. Modern ‘cyclone’ vacuum cleaners use this exact principle to remove the dust, fluff and debris from air, when you empty it into the bin, you are actually emptying the impaction chamber*.
The gas-phase species, however, require a much less complex system. In fact this is nothing more than a couple of stainless steel pipes, these will point backwards so that we can avoid any rain and indeed cloud droplets that me may encounter en-route across the US. We won’t be travelling at anything like the speed that we do when on research aircraft (100 m/s or 360 kph) so inlets are much less of an issue for us. We will have a pair of these inlets, one for the ozone instrument and another for the greenhouse gases unit, this means that we can just let the individual instruments control their own sample flow rates. This is in contrast to the aerosol system which will have carefully balanced flows across the different samplers.
I also have a special optic which will be fitted and it needs a long fibre optic to move the precious photons from the topface of the light collector (cosine collector) to the detector. As it turned out, one of the lads that I did my PhD with, Dave Creasey, is involved in the sales and marketing team for the company (Ocean Optics) we are working with. As soon as I contacted him he fired up the technical team to service our special requests. I last saw him in Amsterdam airport, I forget where he was heading not that my destination springs to mind either, he had just started working for Ocean Optics at the time. A very fruitful meeting in the long run, in fact our planned departure point in the US will be a couple of hours from where he is now based so the prospects for meeting up are quite promising.
The trip includes a wide variety of slightly ‘leftfield’ measurements. But the details of these will come in later missives.
*A few years ago I recall a talk where the team collecting aerosol sample actually used a modified Dyson vacuum cleaner to collect samples. There was a photograph of this installed on the aircraft and it was very clear that it was nothing more than a domestic cleaner sticking out of the top of the cabin. Credit to them, millions goes into the design of the vacuum cleaner (a nod to James Dyson) and they retail for a couple of hundred pounds whereas a ‘proper’ aerosol impactor might be an order of magnitude more.