Wednesday, 9 February 2011

Google Earth as a plume tracker

For 3 weeks in January I was involved in more chemistry flights on the BAE 146 Atmospheric Research Aircraft. The flights were part of the NERC funded ROle of Nighttime chemistry in controlling the Oxidising Capacity of the atmOsphere, RONOCO, field campaign. The idea was to fly through pollution plumes in the hope that we could see some interesting chemistry going on. The mission scientists (that is the people in charge of where we go and what we do during the flight) use cloud forecasts from the Met. Office Mesoscale Model and air quality forecasts from the Met. Office Unified Model amongst other things to decide where is the best place to fly.

On 17th January it was decided that we would do a dawn flight and try to follow a pollution plume that was forecast to be coming from Glasgow and Edinburgh and flowing out over the sea from the Firth of Forth.

Example of the plots available to the mission scientist with aerosol forecast on the left and cloud cover forecast on the right.

Take-off was at 06:00 so scientists were allowed onto the aircraft from 01:00 to allow time for instruments to warm up and be calibrated. We took off from East Midlands Airport (EMA) on time and headed up to 10 000 ft to allow in flight calibrations to be done. Once these were complete we went back to EMA; this may seem like a strange thing to do but it makes sense. At night the lowest altitude we can fly at is 1500 ft so if we want to find out about the structure of the atmosphere below that we need to do what is called a 'missed approach'. This is where we pretend to land at an airport but when we reach 50 ft the pilot pulls up and we take off again. This allows us to get a full vertical profile of the atmosphere and much more information. 

So having got information about the structure of the atmosphere we headed up north to look for our pollution. Once over the sea we could descend to 1500 ft hopefully allowing us to get into the more polluted air closer to the surface. As we approached the area where the plume was predicted we started to see concentrations rising indicating that we were indeed seeing something. We flew north across the plume until concentrations seemed to drop again and then flew back and forwards through the plume offsetting slightly each time so that we were slowly heading further out away from the coast. From the measurements we thought that we were getting a nice picture of the plume but its hard to see when you're looking at the data against time rather than location. This is where Google Earth comes in; Axel Wellpot who works for the Facility for Airborne Atmospheric Measurements (FAAM) had done some clever computing which enabled us to see our data superimposed on a map....and not only that but we could also show the predicted aerosol as well to compare what was seen with the predictions. Have a look at the pretty picture below to see how good it is at showing where we saw the plume.
This shows nitrogen oxides in light blue with higher concentrations shown as taller peaks. The colours underneath are the predicted aerosol with yellow being highest and blue lowest. You can see that the plume was pretty much where it was predicted.

Google Earth could then be used to plan our route back towards the coast flying through the peaks in pollution. So from first impressions it looks like a successful flight in terms of finding and sampling a plume but also a brilliant use of available software allowing the in flight data to tell us the best place to fly next. This could be useful for BORTAS where we will have predictions of where carbon monoxide is highest and will want to try and find those places and fly in and out of the plumes when we locate them.