Measurements of greenhouse gases from a Tall tower

Most observations of weather or trace gas concentrations are made within a few metres of the ground surface. Such measurements are representative of the very local area, say within a few hundred metres of the site. In this project, we want to discover the concentration of trace gases representative of a much wider area - essentially most of the Scottish countryside. To get away from local influencing sources, we rent space on a tall TV Tower near Dundee (it's called 'Angus') and measure the air concentration at a height just over 200 m above the ground surface. Pumps on the ground suck air down a narrrow tube and we analyse the air by passing it through a series of gas analysers. We measure the atmospheric content of CO₂, N₂O, CH₄, CO , H₂ and SF₆. We also make measurements of radon222 at the lower level of 50 magl. Measurements are made continuously and routinely and the data is passed back to Edinburgh via the telephone line. We will shortly we linking this page to real-time data for you to look at.

The figures below show greenhouse gas levels recorded at Tall Tower Angus:

Just as with our aircraft sampling project (AEROCARB), we can use the meteorological technique of trajectory analysis to work out just where the air samples we collected actually came from. The figure below shows the result from one day when the air we collected had come from the Atlantic ocean a few days before we managed to grab it. Information on the concentration of trace gases in the air plus a knowledge of how well-mixed the atmosphere is, helps modellers determine the sources and sinks of greenhouse gases. The project is funded by CarboEurope IP from 2001-2008. In the years 2003-2005, the project was funded by EU Framework V and known as CHIOTTO. From 2006, the project will be subsumed into the AEROCARB project of Framework VI

We also run the Met Office's NAME III model (Numerical Atmospheric-dispersion Modelling Environment) to find out where the air has been before arriving at our Tall Tower Angus sampling station. This is a Lagrangian particle dispersion model, which means it uses meteorological fields from the met office to model the movement of 'particles' within the model environment. These particles represent parcels of air.




Particles are released into the model environment and advected backward in time. Almost all the sources of greenhouse gas are at the ground surface, so whenever a particle comes close to the ground it is recorded and this builds up a 'foot print', as shown to the right. By doing this with many particles we can establish a geographical region where we think the air has been close to the ground surface, and therefore was able to 'collect' surface pollutants, before arriving at the Angus Tower.

It possible to combine the information from these 'footprint' maps with observation data from the Tall Tower to build up a map of where the greenhouse gas emissions might be coming from in the UK. The figure below shows an estimated emissions map for Methane (CH4) for the year 2007. It was created using only the observations and modelled 'footprints' with no prior information about emissions. This is important because it provides independent verification of our current UK emission inventories, which the UK is obliged to have under the UNFCCC agreement. Current emieeions inventories use some observations but are compiled mostly by using emissions factors.