Automated system for monitoring trace C2H2 in ambient air by cavity ring-down spectroscopy combined with sample preconcentration

A fully automated instrument combining a continuous wave cavity ring-down spectrometer and dual-trap sample preconcentration has been implemented for monitoring C(2)H(2) mixing ratios in ambient air. A distributed feedback diode laser operating in the near-infrared region (lambda similar to 1534.973 nm in air) detects C(2)H(2) in absorption via the P(17) rotational line of the (nu(1) + nu(3)) vibrational combination band. The instrument is shown to be capable of fast, quantitative, and precise monitoring of C(2)H(2) mixing ratios, with a detection limit of similar to 8 pptv (parts per trillion by volume). It thus has potential to be deployed for analysis of air samples in many rural and urban environments. In situ measurements were carried out at 30 min intervals over periods of up to 15 h on several days for indoor and outdoor air samples. For indoor air monitored on a Sunday, the C(2)H(2) mixing ratio was stable at 1.45 +/- 0.04 ppbv (parts per billion by volume). On weekdays, both indoor and outside air analyses showed peaks in the range 2-4 ppbv in the early morning and late afternoon that coincided with periods of busy road traffic.