Acrolein Monitor using Quantum Cascade Laser Infrared Absorption

Acrolein (CH2 = CHCHO) is a toxic unsaturated aldehyde that has been classified by the U.S. Environmental Protection Agency (EPA) as a hazardous air pollutant (HAP) because of its adverse health effect, particularly on respiratory systems. There are both anthropogenic and natural sources of acrolein in the environment. Acrolein is produced by combustion sources (e.g., vehicle exhaust, prescribed agricultural burning, cigarette smoke) and industrial sources, including manufacturing facilities of wood products. There is, however, very limited data quantifying the emissions of acrolein from these sources. Also, there are few reports of the ambient levels in surrounding regions that may be impacted by these sources. There is a need of air quality instrumentation for acrolein for routine air quality monitoring in urban areas for health effect assessment, and at specific sites for source assessment studies. EPA Region 10 has identified as a priority issue the development of a measurement technique for monitoring acrolein. EPA is under increased pressure to regulate hazardous air pollutants as required by the 1990 Clean Air Act. In the Phase I program, we demonstrated the feasibility of a quantum cascade (QC) laser-based system for acrolein measurement, offering fast response and high sensitivity (~1 ppbv, 1 sec). The instrument is based on Tunable Infrared Laser Differential Absorption Spectroscopy (TILDAS) using QC lasers. The QC-TILDAS method has distinct advantages over indirect detection methods. Infrared absorption is an absolute, highly specific technique. In the Phase I program, we identified the optimum spectral region for acrolein monitoring. We investigated and identified background suppression methods with chemical scrubbers to remove interferences from the acrolein measurements, critical to achieving sensitive acrolein detection. In addition, we conducted laboratory studies of ambient and source emissions of acrolein. The objective of the Phase II project is to fabricate and demonstrate a fully functional, fast response, cryogen-free QC laser spectrometer to measure acrolein. The instrument will have compact size to fit in a rack mountable box and will be capable of long-term, autonomous operation in the field. It will be able to obtain sensitivities in the parts-per-billion (ppbv) range for source monitoring and sub-ppbv range for ambient conditions. There is a need for commercially available air quality instrumentation for acrolein and other toxic air pollutants. The QC-TILDAS system to be built and demonstrated in this program will have wide commercial applications for both routine air quality monitoring and for source assessment of hazardous air pollutants.