Application of extractive cryogenic inert preconcentration with Fourier transform infrared spectroscopy: Preliminary laboratory and field results

In collaboration with the Jefferson County Department of Health (JCDH) and the Environmental Protection Agency (EPA) Region IV, the University of Alabama in Huntsville (UAHuntsville) developed a near-real-time trace gas monitor using extractive cryocooled inert preconcentration combined with Fourier transform infrared spectroscopy (ECIP-FTIR). The ECIP-FTIR uses a commercial FTIR spectrometer, a commercial long-path IR gas cell, a commercial acoustic Stirling cyrocooler, and two custom parallel cryogen-free cryotraps to autonomously monitor an evolving multi-pollutant suite of volatile organic compounds (VOCs). Every 15 minutes, the system records a trace gas absorption spectrum and the derived trace gas concentrations, using continuous non-preconcentrated sample flow through the gas cell, to achieve detection limits of ~10 parts per billion volume (ppbv). Every 4 hours, the FTIR and gas cell obtain similar data on preconcentrated batch samples that have been thermally desorbed from the cryotrap, to improve detection limits to ~5 parts per trillion volume (pptv).

We present initial laboratory data, as well as field samples collected at the National Space Science and Technology Center (NSSTC) in Huntsville. Laboratory results show the ECIP-FTIR methodology is well suited for a wide range of trace gas research and monitoring applications, including EPA National Air Toxics Trends Stations (NATTS) and National Core monitoring network (NCore). Preliminary field measurements demonstrate the utility of the ECIP-FTIR for monitoring ambient VOC concentrations in a small urban setting, which will prove useful in improving air quality models and in gaining a better understanding of VOC-NOx-O3 interactions.