ENVIRONMENTAL LABORATORY 5


in this experiment had a detection limit of approximately 1.5 ppb, and a range of 1.5 to 3 ppm.


The instrument was calibrated every 30 minutes using a gas standard of 1.8ppm methane in air. The teflon inlet line was attached to the church roof 30 metres above the ground and was protected from the elements using an aluminium funnel and a 2 µm particle filter. The instruments locations are shown in images 1 and 2.


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 findings of the experiment saw several elevated CH4


measurements measured by the GC-FID in


Haddenham church on a specific 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 analysis using a Picarro Cavity Ring-Down Spectroscopy (CRDS) instrument. The results showed a similar measurement between the Ellutia 200 Series GC-FID and Picarro CRDS. This confirmed the impact the high winds had on the levels of methane measured at the site on this specific date.


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


. The Keeling plot of the air samples taken Image 1:The location of where the GC was installed at Tilney-All-Saints Church


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 landfill 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 landfill [7].


To confirm the impact of the landfill on the results, air samples were taken closer to the landfill, 10 m from the active site [7].


Stable and repeatable results In another experiment, the average annual CH4


Image 2: The 200 series as installed within the church tower.


Figure 2. Keeling plot of the air samples taken at Haddenham church between 06:00 and 14:00 UTC on 11 February 2015.


Methane Emission Estimates (InTEM) model is estimated at 13.7 gigagrams yr−1. The results are shown in Table 1 [8].


A range of scenarios were run in WindTrax to investigate the uncertainty in CH4


emissions caused by the CH4


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,


measurement have little effect on the


emission estimate. Uncertainty in estimating the emission area and roughness length have a noticeable effect on CH4


uncertainty in estimating wind speed, resulting in an emission uncertainty of ±19%. The overall uncertainty in CH4


emission,


resulting in an uncertainty of ±3 and ±4 % on modelled CH4 emissions, respectively. WindTrax has the greatest response to the


emission,


calculated as the root of the sum of each component squared, is estimated at ±20% [8].


emission from


the landfill as measured by the same GC instrument used by the churches as part of the experiment was calculated using ∼ 24,000 hourly averaged CH4


data. This was measured by the East


Anglia network and Numerical Atmospheric-dispersion Modelling Environment (NAME) meteorological data in the Inversion Model


The measurements taken by this experiment relied on the development of a tailored instrument which was able to operate effectively in the field, taking data in real time and feeding back analysis. This has allowed researchers to accurately track data in a way which is stable and repeatable.


The future of GC in environmental analysis


Field GC’s continue to play an important specific role in the identification and quantification of common pollutants in the environment, especially when focusing on highly localised areas analysed in field research.


Industrial growth in developing countries and rapidly increasing air pollution levels are primarily responsible for the rising prevalence of the environmental testing application sector in the global GC market. Recent studies in this area have suggested global methane levels are on the rise although a reason is yet to be determined [9,10]. It is clear that GC will play a key role in providing an explanation to this growing global issue as landfill sites and ‘super-farms’ creating further methane output continue to grow in the coming years [10].


References


1. National Atmospheric Emissions Inventory – Overview of Methane Emissions - http://naei.beis.gov.uk/overview/ghg- overview


2. The greenhouse gas methane (CH4 ): Sources and sinks, the


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.


impact of population growth, possible interventions - https://link. springer.com/article/10.1007/BF02208779 3. Chromatography in Environmental Analysis – AWE Magazine – March 2009 https://www.aweimagazine.com/article/ chromatography-in-environmental-analysis-333 4. Environmental Instrumentation Handbook – Gas Chromatography in Environmental Analysis - https://www.hnu. com/papers/GCEA.pdf 5. World Meteorological Organisation – Measurement of Atmospheric Compositions https://www.wmo.int/pages/prog/ www/IMOP/publications/CIMO-Guide/Prelim_2018_ed/8_I_16_ en_MR_clean.pdf


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