Greenhouse Gases in the Atmosphere
Long-term monitoring of the atmosphere is vital in obtaining greater understanding of the processes involved in climate change and ozone depletion. Only when current and past atmospheric mole fractions are known accurately it is possible to identify long-term trends and to study seasonal, diurnal and interannual variability.
Atmospheric models then enable us to deduce the sources and sinks of GHGs from these atmospheric concentration measurements and calculate regional and global emissions estimates.
Measurements & Observations
The presentations in this section introduce greenhouse gas (GHG) atmospheric measurements, outline the theory of ground-based measurements (past and present) and specific techniques as well as methods to best handle and interpret observational data sets.
Theory of Atmospheric Measurements
Ground-based platforms have provided measurements of GHG mole fractions since the first station was opened on Mauna Loa, Hawaii, in 1956. These measurements are key to studying anthropogenically driven climate change and for shaping governmental policy responses. As such, an understanding of how these measurements are made and other key factors (e.g. site location, calibration and interferences) are essential when interpreting and using the observations.
Dr Kieran Stanley and Dr Ann Stavert (University of Bristol)
This presentation gives an overview over trace compounds in the atmosphere and introduces key instrumentation that is used to measure trace compounds, in particular Gas Chromatography (GC), Mass Spectrometry (MS) and optical techniques like Cavity Ring-Down Spectroscopy (CRDS) and Fourier Transform Infrared Spectroscopy (FTIR). It also discusses measurement networks and the interpretation of measurements.
[Kieran Stanley and Ann Stavert: Atmospheric Measurements (PDF, 4.4Mb)]
Calibration: Propagation, Scales and Impact
Dr Ann Stavert (University of Bristol)
Calibration is defined as characterising the instrumental response to a fixed or known quantity of the analyte. This lecture discusses instrument stability and interferences in gas mixtures and how to account for these effects. It also looks at the practical issue of metrological traceability, i.e. the chain of calibrations from international standards down to the individual instrument, and questions of comparability and compatibility.
[Ann Stavert: Calibration: Propagation, Scales and Impact (Content not yet available)]
Gas Sensing and Metrology
Dr Tom Gardiner (National Physical Laboratory – NPL)
Various optical techniques are used for the detection and quantification of greenhouse gases. This presentation focusses on the differences between qualitative and quantitative methods of detection, the information these techniques yield and how the uncertainty of these measurements can be assessed, introducing some of the underlying metrology (science of measurement) issues.
[Tom Gardiner: Gas Sensing and Metrology (PDF, 4,9Mb)]
- [https://www.bipm.org/en/publications/guides/gum.html BIPM: Guide to Uncertainty and Measurements (GUM)]
Remote sensing of GHGs
Dr Neil Humpage (University of Leicester)
Satellites can provide observations of atmospheric concentrations of greenhouse gases using spectroscopic techniques in the shortwave-infrared or thermal infrared spectral range. The main advantage of remote sensing measurements is that they provide global, frequent and densely sampled data that complements the more accurate but sparse in-situ surface and aircraft observations. A major challenge for remote sensing is the indirect nature of the measurements, as the observed light is influenced by a range of processes in the atmosphere which need to be considered in the data analysis. Also, careful validation against ground-based data is essential to ensure the consistency with the in-situ standard. Satellite observations are becoming an important resource for carbon cycle science with more than 10 years of space-based data now available.
[Neil Humpage: Remote Sensing of GHGs (PDF, 6.5Mb)]
Aircraft measurements of GHGs
Dr Grant Allen (University of Manchester)
Aircraft data can provide 3D spatial mapping of wide areas relatively quickly. However, in-situ data collected from aircraft still represent the timestamp and location of the sample in what is still a moving reference frame (i.e. advecting atmosphere). This presentations introduces the UK's Facility for Airborne Atmospheric Measurements (FAAM) and discusses how to analyse and interpret aircraft data.
[Grant Allen: Aircraft measurements of GHGs (PDF, 4.3Mb)]
- [https://www.faam.ac.uk/ Facility for Airborne Atmospheric Measurements]
Atmospheric models are an important tool to investigate the transport and the fate of GHGs in the atmosphere (transport modelling). Models are also used to attack the so-called inverse problem: Given a set of atmospheric measurements, what are the sources and sinks that are consistent with these measurements?
Inverse Modelling: Calculating Emissions from Atmospheric Measurements
Dr Tim Arnold (University of Edinburgh and National Physical Laboratory - NPL)
This presentation provides an understanding of the concepts behind calculating GHG emissions on global and regional scales using in-situ ambient air measurements. Total mole fractions have been routinely measured on the ground for decades using automated in-situ techniques, and flask sampling with analysis at a laboratory. Models and inverse methods have been developed to translate these data into emissions estimates. Each gas has a unique source and sink profile in time and space, and prior knowledge is often very poor. Thus, a lot of research centres around statistical analysis and modelling techniques needed to make meaningful policy-relevant interpretations of GHG measurements.
[Tim Arnold: Calculating Emissions from Atmospheric Measurements (PDF, 3.1Mb)]
Transport Modelling: Atmospheric Modelling of GHGs
Dr Luke Surl (University of Edinburgh)
Atmospheric GHG models range from 0-D box models to high-resolution 3-D models that incorporate detailed dynamical processes. Different models are required to address different scientific questions. What they have in common is that they are useful tools with which to improve knowledge of surface source and sinks of GHGs by confronting model predictions with data (from ground-based, aircraft, or satellite instruments). As such, model evaluation and development has been a core activity in recent ground-based, aircraft, and space-borne measurement campaigns.
[Luke Surl: Atmospheric Modelling of GHGs (PDF, 3.0Mb)]
[The material on this website is based on lectures and activities that were developed for a series of residential summer schools held in 2015 at the University of Edinburgh and in 2016 at the National Oceanography Centre, Southampton [as part of the Greenhouse Gas UK and Global Emissions (GAUGE) / Radiatively Active Gases from the N.Atlantic Region & Climate Change (RAGNARoCC) / Generating Regional Emissions Estimates with a Novel hierarchy of Observations and Upscaled Simulation Experiments (GREENHOUSE) projects] and in 2017 at the National Oceanography Centre, Southampton as part of a NERC Advanced Short Training Course. This website was funded by the NERC Advanced Short Training Course 'Multidisciplinary training in greenhouse gases in the atmosphere, oceans and terrestrial biosphere summer school' (NE/P020615/1). Content was collated by Dr Peter Brown (National Oceanography Centre) and Dr Stephan Matthiesen (University of Edinburgh). More content will be added as it becomes available.]