British Antarctic Survey (BAS) Picarro (G2301) gas analyser is a CO2, CH4, H2O analyser used for long-term atmospheric monitoring. The heart of the Picarro is a sophisticated time-based measurement that uses a laser to quantify spectral features of gas phase molecules in an optical cavity. Picarro unique design enables an effective measurement path length of up to 20 kilometers in a compact cavity, which results in exceptional precision and sensitivity in a small footprint. Picarro uses a patented, high-precision wavelength monitor to maintain absolute spectral position, which combats the drift inherent in all lasers and ensures accurate peak quantification