Tracing the Mercury in the UK Atmosphere – Peaks and Sources

During 2013 total gaseous mercury was monitored at the Auchencorth Moss and Harwell field sites, which are run by the UK’s Centre for Ecology & Hydrology and Ricardo-AEA respectively on behalf of the UK Department for the Environment, Food and Rural Affairs as part of the UK rural heavy metals monitoring network. The sites are the two UK EMEP supersites, part of the cooperative programme for monitoring and evaluation of long-range transmission of air pollutants in Europe. Auchencorth was first established in 1995, and is operated to EMEP level III. It is located about 20 km south-west of Edinburgh (55.450 N, 3.150 W). This is a rural, upland peat site with a large, uniform fetch. Harwell has had air monitoring since the 1970s, and is operated at EMEP level II, located about 26 km south of the city of Oxford (51.571 N, 1.325 W). This is a semi-rural site located near the Harwell Science and Innovation Campus. The Tekran mercury analyser (Model 2537A, Tekran Inc.), is used to measure TGM in air at both sites. It is run at a resolution of 5 minutes, using dual channels allowing for continuous monitoring. Observed concentrations of TGM is at the lower end of the northern hemispherical background level of 1.4-1.7 ng m-3 observed at other sites. The annual averages of TGM for 2013 for Auchencorth and Harwell respectively are: 1.33 and 1.45 ng m-3. Using measurements of other atmospheric species from colocated instruments, we have used the OpenAir Statistical Package for R, to analyse the influence of point sources on observations, specifically looking at the closure of coal fired power stations at Cockenzie and Didcot for Auchencorth and Harwell respectively, which were located within the local area. We also use air mass back trajectories and cluster analysis to assess the long range transport of mercury to the sites, investigating repeated episodic peak events of up to 2.8 ng m-3 observed at both sites during spring 2013.