A £150,000 proton transfer reaction mass spectrometer is being strapped into the cabin of a Dornier-228 small aircraft, owned by the Natural Environment Research Council (NERC) to measure volatile organic compounds, such as benzene and toluene, and oxides of nitrogen as they are emitted from traffic and buildings in the city into the lower atmosphere. The measurements will be compared to the UK Government’s national atmospheric emission inventory to see if the model fits with reality. 

“These are incredibly difficult things to measure,” according to Dr Marvin Shaw, from Lancaster Environment Centre, who is taking part in the £600,000 research project, funded by NERC and the Department of Environment Food and Rural Affairs.

“The machinery is very sensitive and measures in the parts per billion to parts per trillion range. The complicated step is relating the measurement to where it comes from on the ground,” Dr Shaw said.  “This uses a technique called eddy covariance, which has been used on the ground for many years, but we are the first group in Europe to try this from a moving platform. It’s still at proof-of-concept stage - there is no guarantee it will work.”

 “I’m strapped into a chair beside the spectrometer in a very small cabin. The turbulence is unbelievable, the cabin isn’t pressurized so you feel the outside temperature, there are no luxuries, not even a toilet. The instrumentation is challenging to operate, we need an engineering knack as well as a progamming background to sort out any problems, and a knowledge of chemistry to analyse the results.”

The flights, which involve flying as low as possible, at 800 feet above ground, and as slow as possible, started in June and will last a month. The advantage of using the equipment on an aircraft is that it can cover more ground, and so give an integrated picture of pollution and its sources across the city.

Dr Shaw is working on the project with Dr Brian Davison from Lancaster University and with colleagues from the University of York. Together they hope to obtain about 40 hours of measurements over London, and will then spend the next year analyzing the data.

Project leader Professor Nick Hewitt, from Lancaster Environment Centre, hopes the flights over London will show that the technology they are using works and that it can then be applied to rural landscapes, including in the tropics.

“We will be finding out whether we understand the physics and maths well enough, will the machine work in an aircraft and be sensitive enough to measure low concentrations and changes in concentration, can scientists operate in these difficult conditions?” said Professor Hewitt.

“In Malaysia we want to study how large scale changes in land use for agricultural purposes, such as chopping down tropical forests to plant oil palm, is changing the composition of the atmosphere. Trees react with pollutants in the atmosphere like the oxides of nitrogen from vehicle emissions, to create volatile chemical compounds such as ozone and small particles which damage human health and reduce crop yields,” explained Professor Hewitt.  “Governments spend enormous amounts of money trying to control ozone so we need to understand the natural processes that create it.”