15
The instruments locations are shown in images 1 and 2 below.
The data collected at each site was automatically transmitted back to the central laboratory for processing and analysis using a cloud-based data sharing system. Data processing of individual chromatograms was done using IGOR Pro (Wavemetrics, USA) to determine peak height. Measurements from all sites were calibrated to the WMO calibration scale with the hourly WMO calibrated mixing ratios then calculated using Openair in R [7].
One of the most interesting fi ndings of
the experiment saw several elevated CH4 measurements measured by the GC-FID in Haddenham church on a specifi c day (Figure 1). This happened during high winds from the south-east, which impacted the amount of CH4
measured in a way
which was inconsistent with previous measurements. Air samples were collected in Tedlar bags at the same time and at the same location under the same conditions every 30 minutes and analysed later off site for CH4
Down Spectroscopy (CRDS) instrument. The results showed a similar measurement between the Ellutia 200 Series GC-FID and Picarro CRDS. This confi rmed the impact the high winds had on the levels of methane measured at the site on this specifi c date.
air samples taken at Haddenham church between 06:00 and 14:00 UTC on 11th February 2015 estimated the δ 13C isotopic signature at −58.3 ‰ (Figure 2). The typical δ 13C isotopic signature value for a landfi ll in the south-east of the UK has been estimated to be −58 ± 3 ‰. This is a clear difference between other possible sources for the methane measured and strongly suggests that the air measured at the church had come from a landfi ll [7].
The measurements from Figure 2 were taken using the Keeling plot which is the isotope ratio of respiration in the absence of dilution by atmospheric CO2
To confi rm the impact of the landfi ll on the results, air samples were taken closer to the landfi ll, 10 m from the active site [7].
. The Keeling plot of the
analysis using a Picarro Cavity Ring-
Image 1: The location of where the GC was installed at Tilney-All-Saints Church.
Figure 2. Keeling plot of the air samples taken at Haddenham church between 06:00 and 14:00 UTC on 11 February 2015.
Image 2: The 200 series as installed within the church tower.
and Numerical Atmospheric-dispersion Modelling Environment (NAME) meteorological data in the Inversion Model Methane Emission Estimates (InTEM) model is estimated at 13.7 gigagrams yr−1. The results are shown in Table 1 below [8].
the same GC instrument used by the churches as part of the experiment was calculated using ∼ 24,000 hourly averaged CH4
Stable and repeatable results In another experiment, the average annual CH4
emission from the landfi ll as measured by data. This was measured by the East Anglia network
Table 1: Methane emission estimates from the landfi ll at the Waterbeach Waste Management Park as calculated by the WindTrax and Gaussian plume approaches for the case study and the annual estimates for the Gaussian plume and InTEM inversion modelling approach for 2012– 2014. (8) WindTrax is a software for simulating atmospheric dispersion. Whereas the Gaussian plume approach is a mathematical model used to estimate the concentration of pollutants at a point at some distance from the source of emission.
A range of scenarios were run in WindTrax to investigate the uncertainty in CH4 caused by the CH4
emissions
on the emission estimate. Uncertainty in estimating the emission area and roughness length have a noticeable effect on CH4
Figure 1. Methane mixing ratios measured by the GC-FID in Haddenham church on 11 February 2015 are presented in grey. Matching methane mixing ratios collected in Tedlar bags on 11 February 21015 and analysed on the 20 February 2015 using a Picarro CRDS at Royal Holloway, University of London, are presented as red points.
squared, is estimated at ±20% [8].
uncertainty in estimating wind speed, resulting in an emission uncertainty of ±19%. The overall uncertainty in CH4
% on modelled CH4
measurement, the wind speed measurement, estimating the roughness length and estimating the Monin–Obukhov length. Realistic uncertainty in the Monin– Obukhov length and instrument uncertainty for the CH4
measurement have little effect emission, resulting in an uncertainty of ±3 and ±4
emissions, respectively. WindTrax has the greatest response to the emission, calculated as the root of the sum of each component
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