The MOYA projects PI Euan Nisbet will be convening a session on methane in the AGU Fall Meeting. This years AGU will be held in Washington, D.C. from the 10th-14th of December. Abstract submission closes on the 1st of August 2018 so get writing!
The global burden of atmospheric methane has exhibited periods of both rapid growth and stagnation over the past two decades, with unexplained rapid growth since 2014. This growth has been accompanied by a negative isotopic shift (δ13C–CH4), reversing the trend of the past two centuries. Methane does not have a single dominant source, but rather a wide spectrum of anthropogenic and natural sources. This diversity of uncertain sources has led to a number of recent explanations for recent growth including: tropical wetlands, livestock, fossil fuels (coupled with declining biomass burning), and changes in the methane sink (via reaction with OH). The warming impact of methane’s unexpected growth is now the largest deviation from the Paris Agreement. This session invites work that investigates processes controlling the methane budget using in situ measurements, satellite observations, and modeling, as well as the ways in which emissions can be reduced.
A few weeks ago, the MOYA team completed the first campaign on the Atmospheric Research Aircraft (run by FAAM). I was not in the field in Senegal, but instead I was doing weather forecasting, flight planning and monitoring of the data from back home in the UK. Although there was no wiggle room in the packed schedule, the team managed to get in 4 exciting science flights, and saw different things in each one! Here’s a rundown of what they got up to…
On Tuesday 28 February 2017, they flew inland over a region of forest fires in Senegal. We wanted to sample the emissions from these fires, and they managed to do just that! The picture below shows some of the methane, carbon dioxide and carbon monoxide traces along the flight track. The big spikes show the places where they flew through the fire plumes. They saw huge spikes in all these gases – up to 500 ppb extra of methane, on top of the usual 1850 ppb in this region in this season. That’s about an extra 27%!
We should be able to find out a lot about what gases and particles are in these fire plumes when we analyse these measurements – I’m not sure if anyone has ever flown directly over the fires to measure the emissions before! Some of the air inlets experienced a smoky smell and some strong turbulence from the heat from the fires, as well as a bird strike. All in the name of science!
Next morning, the crew flew back over a similar region of the Casamance, and this time the visibility was very poor. You can see from the photo just how smoky it was. Sampling these fires two days in a row will allow us to find out how variable the emissions are from day to day.
After refuelling in Dakar, the next flight was off the coast, with the aim of sampling fire emissions as they are blown out to sea. The measurements showed there were layers with high levels of ozone, carbon monoxide and nitrogen oxides as well as moderate methane, which may well have been from the fires. The figure below shows the carbon monoxide (CO) levels as the aircraft flew back and forth at different heights. At 5000 feet, there’s a layer of high CO that isn’t present above or below that height. The next day, they flew off the coast again and measured something similar, which one scientist called a “complex sandwiched air mass”!
Dr Grant Allen, one of the lead scientists on the flights, said of the experience:
“The flying was very challenging (and exciting!). Flying as low as 500 ft over the savannah and through intense fire plumes is a rare experience for most and I’ll admit to being nervous on occasion. However, the professionalism of FAAM and the expert training of the pilots and aircraft engineers means we are always in safe hands. The team recorded the most intense sampling (vertically) of a near-source fire plume ever performed with the FAAM research aircraft and the data will keep the science team busy for many months and years to come. We expect to analyse the carbon-isotopic fractionation of biomass burning signatures for this crucial regional methane source and provide new chemical and aerosol measurements of fire plumes.”
So started the first of the MOYA flight campaigns. We are all hoping we will have the same success and luck in the future!
– Dr Michelle Cain, University of Cambridge