High-precision carbon dioxide instrumentation

The facility deploys cavity ring down spectroscopy (CRDS) instruments for the measurement of atmospheric carbon CO2 concentrations. The CRDS instruments provide a stable and precise measurement of the concentrations of the most important greenhouse gases (CO2, methane (CH4) and water vapour) to the parts per billion level with negligible drift. 

These measurements have successfully been used with a Bayesian inverse modelling approach to independently improve the identification of CO2 and CH4 sources and sinks as well as to identify potential source locations to independently assess the efficacy of mitigation efforts.

The instrumentation meets the World Meteorological Organisation’s data quality objectives for global atmospheric watch stations and the integrated carbon observation system atmospheric station specifications.   

Technical Specifications


Cavity ring down spectroscopy instruments:

  • Cape Point - Located at Cape Point Global Atmospheric Watch station and has been in operation since 2014. The instrument measures CO2 and CH4 concentrations in marine and air masses.
  • KwaDela/Kwazamokuhle - The instrument is operated by the North-West University to assess the concentration of CO2, CH4 and carbon monoxide as a result of domestic combustion to attribute the contribution of domestic combustion to local air pollution.
  • Elandsfontein - The instrument is located in the regional background site of the industrialised region of the Mpumalanga Highveld. 
  • Lephalale - The instrument is located in the regional background site of the rapidly industrialising Waterberg region. 
Instrumentation specifications
Specification CO2 CO CH4 H20
Atmospheric range ~400 000 ppb ~1 500 ppb ~ 1 800 ppb ~20 000ppm 
Precision (5 sec / 5 min/ 60 min) <50 ppb / 20 ppb / 10 ppb <15 ppb / 1.5 ppb / 1 ppb <1ppb / 0.5 ppb / 0.3 ppb <30 ppm / 5 ppm
Max Drift (24 hours / 1 month) 100ppb / 500ppb 10ppb / 50 ppb 1 ppb / 3 ppb 100 ppm ± 55 of reading
Max uncertainty using reference gas (1 hr average, 2 σ) <50 ppb <1 ppb < 0.5ppb NA
Operating range 0-1000 ppm 0-5 ppm 0-20 ppm 0-7%v H2O


Key Concept

Cavity ring down spectroscopy technique
The cavity ring down spectroscopy technique utilises a time-based measurement that uses a laser to quantify the spectral features of gas phase molecules in the instrument’s optical cavity. Due to the configuration of mirrors in the optical cavity, a measurement path length of ~30 km is created, which provides precision and sensitivity.