The use of continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared (IR) region has great potential for the design of ultra-sensitive, compact, robust and cost-effective novel optical sensors capable of detecting trace species present in the atmosphere. The research work presented in this thesis focuses on the development and implementation of a fully automated, cryogen-free and compact cw-CRD spectrometer, combined with adsorbent filled dual-trap sample pre-concentration for monitoring trace C₂H₂ mixing ratios in ambient air.