Development of extractive FTIR spectroscopy with cryogen-free low-temperature preconcentration for autonomous measurements of gaseous air toxics.

摘要

An experimental atmospheric air quality monitoring system has been developed using a commercial Fourier Transform Infrared spectrometer (FTIR), a commercial long-path gas cell, a commercial acoustic Stirling cryocooler, and dual parallel cryogen-free cryotraps. This device includes several integrated subsystems in order to monitor ambient air toxics in an autonomous system with on-board quality assurance/quality control (QA/QC). Every 15 minutes, the system records a co-added FTIR interferogram using continuous, unconcentrated flow through the gas cell. From this interferogram, the spectral processing algorithm calculates a corresponding absorption spectrum and derives trace gas concentrations. Every four hours, the system takes comparable data on preconcentrated batch samples that are thermally desorbed from the cryotrap. During the system calibration cycle, the system acquires QA/QC measurements made in a similar fashion. The preliminary results presented will demonstrate the utility of this technology for a wide range of trace gas research and monitoring applications, including the Environmental Protection Agency (EPA) National Air Toxics Trends Stations (NATTS) network.