Application of Extractive Fourier Transform Infrared Spectroscopy with Cryogenic Preconcentration: Preliminary Laboratory Results
P.I. Buckley1, D.A. Bowdle2 and M.J. Newchurch1
1University of Alabama, 301 Sparkman Drive, Huntsville, AL 35899; 256-961-7881, E-mail: buckley@nsstc.uah.edu
2Earth Systems Science Center, Pennsylvania State University, University Park, PA 16802
In collaboration with the Jefferson County Department of Health and the Environmental Protection Agency (EPA) Region IV, the University of Alabama in Huntsville recently developed a near-real-time trace gas monitor using extractive Fourier Transform Infrared Spectroscopy (FTIR) in concert with Extractive Cryocooled Inert Preconcentration (ECIP). The ECIP-FTIR uses a commercial FTIR spectrometer, a commercial long-path Infrared (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. 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 and a signal-to-noise ratio of ~105. 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 and improving the signal-to-noise ratio.
We present preliminary laboratory data collected at the National Space Science and Technology Center in Huntsville. These 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 and National Core monitoring network.
Figure 1. The ECIP-FTIR Instrument Layout. Panel A shows the entire instrument layout. From left to right, the FTIR, cryocooler, and electronics compartment with operations personal computer can be seen. Panel B shows the fluid subsystem including flow passages, inlet pumps, and shut off and flow selection valves. Panel C shows the optical subsystem with emphasis on the FTIR and gas cell. Panel D show the cryogenic subsystem and Quality Assurance/Quality Control manifold along with mass flow controllers (green boxes). Panel E shows the data acquisition system and mass flow junction boxes.
Figure 2. IR Spectrum of trace methanol in air taken at 1cm-1 resolution and 15 minute co-addition. The blue trace is the measured methanol spectrum. The green trace is the deresolved library spectrum.