Atmospheric trace gas measurements
The Centre’s historical strength is in atmospheric trace gas measurements, and in developing and using novel optical techniques. These include solar Fourier Transform Infrared (FTIR) remote sensing, in situ FTIR and open path FTIR. More recently we introduced other techniques such as the Biogenic Ambient Atmospheric Sampling System (BAASS) and a range of commercially available analysers (O3, NOx, etc.) to expand the range of interests into volatile organics, biomass burning emissions and other species.
Contacts: Clare Murphy, Nicholas Deutscher, Nicholas Jones
Solar FTIR remote sensing
Ground based solar infrared remote sensing is able to detect and quantify a wide range of atmospheric trace gas species by analysis of the absorption of solar radiation in the infrared and near-infrared regions. CAC operates stations at Wollongong and Darwin as part of two global networks of ground-based solar infrared observatories, the Total Carbon Column Observing Network (TCCON; Wunch et al., 2011) since 2005 and the Network for the Detection of Atmospheric Composition Change (NDACC) since 1995.
TCCON began measurements in 2004 and focuses on high precision, high accuracy measurements of greenhouse gases such as carbon dioxide and methane from near-infrared solar spectra; TCCON data are used extensively to validate measurements made by orbiting satellites such as the GOSAT and OCO-2 ( satellites and to validate and compare output from models of global atmospheric trace gases and the carbon cycle. TCCON has become the de facto “gold standard” for satellite and model validation, providing the crucial calibration link between remote sensing and in situ measurements. Both Wollongong and Darwin stations are a part of TCCON. For further detail see the TCCON website and publications list.
NDACC (originally NDSC, Network for Detection of Stratospheric Change) operates in the mid-infrared and measures over 40 stratospheric and tropospheric trace gases. We have made MIR measurements in Wollongong continuously since 1995. The original focus of NDSC/NDACC was the stratosphere and the chemistry of ozone and ozone-depleting substances; in recent years NDACC focus has moved downwards to include the troposphere. Like TCCON, NDACC data are also used extensively in satellite and model validation for a wide range of species.
In the Greenhouse Gas Monitor (GGM) project, we are investigating the limits of low resolution mobile solar FTS instruments for cost-effective deployment to quantify local and regional greenhouse gas sources and sinks.
In situ FTIR trace gas analysis
FTIR spectroscopy measures the absorption of infrared radiation by a sample over a broad spectral range, in which many trace gas species in air may absorb. Analysis of the FTIR spectrum of air provides a technique for simultaneous, continuous, multi-species trace gas analysis with high accuracy and precision. Over several years we have developed a complete FTIR in situ trace gas analyser (Griffith et al., 2012) which samples air into a multi-pass cell for analysis. We have used the analyser in a number of applications such as clean air background measurements (Griffith et al., 2011) and agricultural and forest exchange measurements). In 2010 the UoW-CAC FTIR trace gas analyser was licensed to Australian air monitoring company Ecotech Pty Ltd., which is now commercially available.
Open path FTIR trace gas analysis
FTIR spectroscopy over an open-air path complements in situ analysis by probing the air over an open path of up to several hundred metres rather than sampling at a point. OP-FTIR is able to detect plumes from agricultural and industrial sources and because there is no sampling of air involved, difficult-to-sample species such as ammonia from agriculture are well suited to open path spectroscopy. We have also developed an open-path FTIR system (now produced by Bruker Optics, Germany) and used it extensively in agricultural measurements of methane emissions from free-ranging cattle and sheep.
The Biogenic Ambient Atmospheric Sampling System (BAASS) comprises a Markes pre-concentration/injection system and an Agilent Gas Chromatography Mass Spectrometer. It can make measurements of the chemicals emitted by trees (biogenic volatile organic compounds or VOCs). There is growing recognition of the importance of these biogenic emissions on atmospheric chemistry and air quality within urban air-sheds (especially in cities surrounded by densely forested regions). Within Australia, many of the major cities have very high levels of atmospheric VOCs that are predominantly emitted by vegetation within the cities and emissions originating from nearby natural forested regions. These chemicals react in the atmosphere leading to increased concentrations of fine particulates and ozone, causing poor air quality and adverse health impacts. See “The COALA Campaign”.
- Griffith, D. W. T., Deutscher, N. M., Caldow, C. G. R., Kettlewell, G., Riggenbach, M., and Hammer, S.: A Fourier transform infrared trace gas analyser for atmospheric applications, Atmospheric Measurement Techniques, 5, 2481-2498, 10.5194/amtd-5-3717-2012, 2012.
- Wunch, D., Toon, G. C., Blavier, J.-F., Washenfelder, R., Notholt, J., Connor, B., Griffith, D. W. T., and Wennberg, P. O.: The Total Carbon Column Observing Network (TCCON), Philosophical Transactions of the Royal Society A 369, 2087-2112, 2011.