Recent advances in measurement techniques for atmospheric carbon monoxide and nitrous oxide observations
Abstract. Carbon monoxide (CO) and nitrous oxide ( N2O ) are two
key parameters in the observation of the atmosphere, relevant to air
quality and climate change, respectively. For CO, various analytical
techniques have been in use over the last few decades. In contrast, N2O 
was mainly measured using gas chromatography (GC) with an electron capture
detector (ECD). In recent years, new spectroscopic methods have become
available which are suitable for both CO and N2O . These include
infrared (IR) spectroscopic techniques such as cavity ring-down
spectroscopy (CRDS), off-axis integrated cavity output spectroscopy
(OA-ICOS) and Fourier transform infrared spectroscopy (FTIR). Corresponding
instruments became recently commercially available and are increasingly used
at atmospheric monitoring stations. We analysed results obtained through
performance audits conducted within the framework of the Global Atmosphere
Watch (GAW) quality management system of the World Meteorology Organization
(WMO). These results reveal that current spectroscopic measurement
techniques have clear advantages with respect to data quality objectives
compared to more traditional methods for measuring CO and N2O . Further,
they allow for a smooth continuation of historic CO and N2O time series.
However, special care is required concerning potential water vapour
interference on the CO amount fraction reported by near-IR CRDS instruments.
This is reflected in the results of parallel measurement campaigns, which
clearly indicate that drying the sample air leads to an improved accuracy
of CO measurements with such near-IR CRDS instruments.