UAHuntsville is building a new sensor for atmospheric trace gases, including hazardous air pollutants, for the Jefferson County Department of Health (JCDH), in Birmingham, Alabama, and for the Environmental Protection (EPA) Office of Air and Radiation (OAR). The sensor uses extractive sampling with a commercial Fourier Transform Infrared (FTIR) spectrometer, a commercial long-path IR gas cell, and an in-house cryogenic preconcentrator for the trace gases. This methodology is called Extractive Cryocooled Preconcentration – FTIR, or ECP-FTIR, to distinguish it from the well-known Extractive and Open-Path FTIR methods (E-FTIR and OP-FTIR). The sensor includes several integrated subsystems (thermal, electrical, mechanical, optical, chemical, fluid, cryogenic, vacuum, sensors, data, controls, and communications) in an autonomous unattended system with on-board quality control and quality assurance (QA/QC).
Every 15 minutes, the system will record a co-added FTIR interferogram, its corresponding trace gas spectrum, and the derived trace gas concentrations, using continuous non-concentrated sample flow through the gas cell. Every 4 hours, the FTIR and gas cell will obtain similar data on batch samples that have been thermally desorbed from the preconcentrator. Each day, the system will obtain the same type of data from the QA/QC manifold (calibration and spike gases). The gas cell and the cryotrap will be reconditioned and reinitialized before and after the batch samples and the QA/QC samples. Every twelfth day, these procedures will be modified to synchronize the FTIR measurements with 24-hour measurements from collocated EPA samplers.
The next steps in the ECP-FTIR development process include final assembly, testing, and calibration in the laboratory; sampling from the atmosphere above the laboratory, and shakedown at the EPA Air Quality Staion in south Huntsville. After these preliminary studies, the ECP-FTIR sensor will be deployed at multiple JCDH air quality stations in Birmingham over a one-year period. UAHuntsville will analyze the resulting measurements, assess the sensor performance, and recommend improvements in sensor design and operations. This project is demonstrating that low-cost sensors can be developed for non-specialists to obtain continuous real-time measurements of HAPS and other atmospheric trace gas with high sensitivity and high temporal resolution.
David Bowdle, ESSC Research Scientist, is the primary developer of the ECP-FTIR. Patrick Buckley, ATS Graduate Student in Atmospheric Chemistry, is building and testing the instrument for his Masters Thesis. Collaborators include Michael Newchurch, ATS Professor; Noor Gillani, ESSC Principal Research Scientist; and Randy Dillard, JCDH Air Monitoring Supervisor.