A tunable diode laser spectrometer for high precision concentration and ratio measurements of long-lived atmospheric gases

The ambient fluctuations of long-lived atmospheric gases such as carbon dioxide, methane, and carbonyl sulfide, to name a few, contain important information about sources, sinks and potential secular trends. Since such fluctuations can be quite small, typically less than a few percent, high precision instruments are required. In this paper, the authors describe a versatile tunable diode laser system for this purpose. This system employs a number of novel features for increased system control and versatility. In addition to high precision, such versatility enables us to acquire the ratio of 2 spectral features with high precision, even when the signal amplitudes are a factor of 26 different and when the spectral features are separated by as much as 0.424 cm-1. This capability can be used to address important applications in atmospheric studies