Location: 51°25’35.63″N, 0°33’40.14″W
The Egham site has a continuous CH4 record since late 1995 and CO since 1996. The CO2 record dates from 1999. The continuous CO2 and CH4 record is currently measured using a cavity ringdown spectrometer (Picarro G1301) with calibration every 7 days and a target gas sample every 2 days. Other species measured are 222Rn and H2.
Flask sampling occurs every 7 days to give measurements of δ13C on CH4 as well as a check on the concentration measurements of CO2 and CH4.
The Royal Holloway, University of London (RHUL)
laboratory is situated 32 km WSW of the centre of London on the first significant incline to the west of the conurbation. The ground altitude is about 45 m above mean sea level, and 30 m above the level of the nearby Thames floodplain. The air intake is a further 15 m above ground level. This site, which is approximately 7 km SW of the perimeter of Heathrow airport, is ideal for local, regional and background studies. Windsor Great Park is 2 km to the west, covering an area of approximately 30 km2. To the SW of the collection site is an area that is mostly suburbia interspersed with woodland and the Surrey heathlands.
The eastern sector is dominated by the London conurbation. Wind direction is a very important parameter for a monitoring site on the western edge of London. Trajectories for the southwesterly air streams typically approach above the English Channel, and descend over 80-100 km of relatively rural / small urban character before reaching the site. Air from this direction can have carbon gas mixing ratios close to those at North Atlantic background stations, particularly during summer months when the north-easterly tracking Azores high pressure system reaches southern England, while the Mace Head background station in western Ireland remains under the influence of Canadian air masses and their associated carbon gas emissions. Air streams from the north-east often pass along the North Sea from Arctic regions, then over 80-100 km of rural East Anglia before reaching north-west London and on to RHUL. Air arriving from the eastern sector has passed over the London conurbation sampling greenhouse gas and pollutant emissions. Sometimes these are Arctic air masses that have moved down the North Sea before heading inland over the Thames basin, at other times they represent air masses from Russia that have traversed industrial northern Europe before reaching London.