Greenhouse gas measurements from a UK network of tall towers: technical description and first results

A network of tall tower measurement stations was set up in 2012 across the United Kingdom to expand measurements made at the long-term background northern hemispheric site, Mace Head, Ireland. Reliable and precise in situ greenhouse gas (GHG) analysis systems were developed and deployed at three sites in the UK with automated custom-built instrumentation measuring a suite of GHGs. The UK Deriving Emissions linked to Climate Change (UK DECC) network uses tall (165–230 m) open lattice telecommunications towers, which provide a convenient platform for boundary layer trace gas sampling. In this paper we describe the automated measurement system and first results from the UK DECC network for CO 2 , CH 4 , N 2 O, SF 6 , CO and H 2 . CO 2 and CH 4 are measured at all of the UK DECC sites by cavity ring-down spectroscopy (CRDS) with multiple inlet heights at two of the three tall tower sites to assess for boundary layer stratification. The long-term 1-minute mean precisions (1 σ ) of CRDS measurements at background mole fractions for January 2012 to September 2015 is −1 for CO 2 and −1 for CH 4 . N 2 O and SF 6 are measured at three of the sites, and CO and H2 measurements are made at two of the sites, from a single inlet height using gas chromatography (GC) with an electron capture detector (ECD) or reduction gas analyser (RGA). Repeatability of individual injections (1 σ ) on GC and RGA instruments between January 2012 and September 2015 for CH 4 , N 2 O, SF 6 , CO and H 2 measurements made using GC-ECD or -RGA were −1 , −1 , −1 , −1 and −1 , respectively. Instrumentation in the network is fully automated and includes sensors for measuring a variety of instrumental parameters such as flow, pressures, and sampling temperatures. Automated alerts are generated and emailed to site operators when instrumental parameters are not within defined set ranges. Automated instrument shutdowns occur for critical errors such as carrier gas flow rate deviations. Results from the network give good spatial and temporal coverage of atmospheric mixing ratios within the UK since early 2012. Results also show that all measured GHGs are increasing in mole fraction over the selected reporting period and, except for SF 6 , exhibit a seasonal trend. CO 2 and CH 4 also show strong diurnal cycles, with night-time maxima and daytime minima in mole fractions. These data are used to produce independent emission estimates for comparison with the UK national inventory based on independent methods.