Extractive FTIR spectroscopy with cryogen-free low-temperature inert preconcentration for autonomous measurements of atmospheric organics: 1: Instrument development and preliminary performance.

In collaboration with the Jefferson County Department of Health and the Environmental Protection Agency (EPA), the University of Alabama in Huntsville developed a novel sensor for detecting very low levels of volatile organic compounds (VOCs). This sensor uses a commercial Fourier-transform infrared (FTIR) spectrometer, a commercial long-path IR gas cell, a commercial acoustic Stirling cyrocooler, and a custom cryogen-free cryotrap to improve sensitivity in an autonomous system with on-board quality control and quality assurance. Laboratory and initial field results show this methodology is sensitive to and well-suited for a wide variety of VOC atmospheric research and monitoring applications, including EPA National Air Toxics Trends Stations and the National Core monitoring network.

Fourier transform infrared spectroscopy of size-segregated aerosol deposits on foil substrates.

A method based on Fourier transform infrared (FTIR) double-pass transmittance spectroscopy was developed for determining functional group loading in size-segregated ambient aerosol deposits. The impactor employed for sample collection utilized rotating stages, which produced uniform particulate matter (PM) deposits on standard Al foil substrates. Each sample was analyzed without extraction using an FTIR spectrometer equipped with a reflectometer accessory. The use of the reflectometer obviated the need for infrared window materials as substrates. (NH(4))(2)SO(4) aerosol generated under laboratory conditions were used to calibrate deposit mass to the band strength of the relatively isolated nu(4) bending mode of SO(2-)(4) centered near 620 cm(-1). Atmospheric PM was sampled during the summer of 2004 in Huntsville, Ala. Sulfate concentrations determined in this initial study correlated well with measurements made by collocated EPA air samplers.