By Dr Jennifer Muller, University of Manchester
The last day of the August aircraft MAMM campaign (19 August) was all about sampling the methane closer to home as well as actually getting back to Cranfield; leaving the Arctic wetland methane behind us (until the September campaign of course). The day consisted of two flights, the first one was a straightforward transit flight from Kiruna, Sweden, to Aberdeen, Scotland; the second was a science flight off the East coast of England to sample methane leaking from gas rigs in the North Sea.
In Aberdeen we stopped for refuelling the aircraft and a short break. Overlooking the landscape taking off from Aberdeen, with its many farms and agricultural fields, villages, towns and roads as far as they eye can see, it really brought home to me, how we humans have changed the surface of the Earth. What a contrast to the Arctic, where we had just been, where forests, bogs, lakes stretch for miles on end, with just single log cabins, dirt tracks and small parcels of fields interspersed in between. There humans have not transformed the landscape completely yet.
The mission for the second flight of the day was to sample methane that comes from anthropogenic or also called "man-made" activities: offshore extraction of natural gas. Natural gas mostly consists of methane, which we burn in our home in gas boilers, heaters and cooking stoves and it's an important energy source. Beneath the North Sea, there are plenty of gas deposits that are currently being exploited and the science mission for this final flight was see whether we could measure methane coming from a group of gas rigs from which we had observed methane leaks the year before.
Based on wind directions, GPS position and the timing of the increased levels of methane observed in 2012, we worked out that the leak must have then come from the Leman gas fields. The Leman complex consists of several gas rigs that are close to each other to form a group not too far from the mainland, and the extracted gas is piped to Bacton gas terminal at the UK's Norfolk coast.
To understand and estimate how much additional methane in the air comes from these gas rigs, one needs to sample the clean upwind air, as well the downwind air that has the gas rig methane in it; and in very simple terms, the difference between "dirty" and "clean" can then be attributed to the gas extraction activities.
The pilots managed to fly low in the boundary layer close to the sea surface, effectively flying a big box pattern around the rigs. Luckily there wasn't much helicopter and other air traffic and we could stay down low to do the track of the box several times, and indeed we measured higher levels of methane downwind of the rigs!
Seeing concentrations shoot up on instrument displays gives a certain kind of thrill and excitement, although of course the extra methane in the atmosphere is not necessarily good! Being a scientist can be a weird thing sometimes...
Similar to the Arctic methane sampling, we had a range of instruments and sampling approaches for this flight: one instrument measured concentrations very accurately, but somewhat slowly (1 measurement every second, i.e. one point for every 100 m of the flight track), another instrument (the one I am working with) was set to sample very fast (10 measurements per second, i.e. means 1 measurement point every 10 m) and then "whole air sample" collection using canisters and air sample bags. Because you can only fill a limited number of canisters and bags during any one flight, you need to make each individual sample count, and fill the canister at the right time. These whole air samples are later analysed back in the laboratory, to give the fingerprint, i.e. isotopic ratio of the methane. The isotopic ratio will be useful to clearly identify this methane to be originating from the gas rigs and hence fossil gas, rather than from other methane sources which then got transported to the North Sea from further afield (for details on isotopic fingerprinting, check out the previous blog posts).
Collecting the whole air samples was rather interesting on this flight, as some of the plumes with high methane were very narrow- that means they lasted just a few seconds- so the whole air samplers (Dave Lowry and Mathias Lanoiselle from Royal Holloway University of London) had to have their eyes locked onto the fast methane display, and fast fingers to trigger the sample collection. I don't know who was more at the edge of the seat -- me or them? Me, because I tried to call out the large concentration increases, or them, because they actually had to make split second decisions on whether to fill their bags or not!
In the end, the flight went really well and we arrived back in Cranfield in the late afternoon, making it yet another long day. The few days in the short August MAMM campaign were packed full of science, and it certainly felt like we've been away on campaign for weeks. Although my brain and body feel a bit bombed out from all the early mornings and short nights, with more hours being airborne than I care to count, I feel massively privileged to work as a scientist on this aircraft, with an extraordinary experienced team of pilots, engineers, operations and flight managers and of course mission & instrument scientists, who all pull out all the stops and contribute their expertise to make a misson happen and work out for the best, always, till the very end.
Previously in this series: