Grantee Research Project Results
Final Report: Acrolein Monitor Using Quantum Cascade Laser Infrared Absorption
EPA Contract Number: EPD07077Title: Acrolein Monitor Using Quantum Cascade Laser Infrared Absorption
Investigators: Shorter, Joanne H
Small Business: Aerodyne Research Inc.
EPA Contact: Richards, April
Phase: II
Project Period: May 1, 2007 through May 31, 2009
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2007) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Pollution
Description:
Acrolein (CH2=CHCHO) is a toxic unsaturated aldehyde that has been identified in the U.S. Clean Air Act as a hazardous air pollutant (HAP). The purpose of this EPA SBIR project is to develop a fast response quantum cascade (QC) laser system based upon the Tunable Infrared Laser Differential Absorption Spectroscopy method (TILDAS). The instrument will allow for selective high sensitivity real-time measurement of acrolein, overcoming the limitations in both sensitivity and time response of present acrolein monitoring methods.
Improved measurement methods are needed to identify acrolein sources and to monitor its presence in ambient air. Current analytical methods for source monitoring (EPA method 18 and CARB 430) and ambient monitoring (EPA method TO-11A) rely on derivatization procedures and are not sufficient. In these standard methods, samples are collected on a solid sorbent cartridge coated with 2,4 di-nitro-phenylhydrazine (DNPH) or other suitable derivatization agent, followed by solvent desorption of the cartridge, and liquid injection of the eluent for high-pressure liquid chromatography (HPLC) and UV-visible absorption analysis (1999; Ho and Yu, 2002; Ho and Yu, 2004). These methods have significant disadvantages as they have time responses on the order of minutes or hours, require consumables which might be hazardous to handle, and have problems with sample loss. Improved technologies are clearly required to provide ambient monitoring of acrolein.
The objective of this EPA SBIR project is the development of a fast response novel quantum cascade (QC) laser system based on the Tunable Infrared Laser Differential Absorption Spectroscopy method (TILDAS). The instrument is designed for the sensitive and selective real-time measurement of acrolein, obtaining sensitivities in the parts-per-billion (ppb) range for source monitoring and parts-per-trillion (ppt) range for ambient conditions. We have constructed a compact, noncryogenic room temperature continuous wave quantum cascade laser (RT-cw QCL)-based instrument to meet these requirements. The instrument is a fully integrated electro-optical system, easy to operate, and capable of providing real-time measurements with high time resolution (better than one second). The instrument does not require calibration gases since retrieved concentrations are based on fitting the absorbance spectra to the calibrated linestrengths and pathlength of the instrument.
Summary/Accomplishments (Outputs/Outcomes):
In the Phase II project, Aerodyne has designed and constructed a compact quantum cascade laser instrument that is totally noncryogenic, easy to operate, and capable of providing real-time measurements with high spectral and time resolution. All cryogens have been eliminated while achieving excellent measurement sensitivity through the combination of a room temperature continuous wave quantum cascade laser (RT-cw QCL) and a thermoelectrically (TE) cooled infrared detector. The RT-cw QC laser not only provides higher laser power than RT-pulsed QCLs, but also it has extremely narrow laser linewidth for high spectral resolution. This narrow linewidth is critical to sensitive and specific monitoring of acrolein. It allows the resolution of acrolein from ethylene and water interferences in its spectral measurement region.
A major problem in the detection of acrolein in the 10 micron region is the presence of nearby ethylene lines. Because ethylene is typically found at high levels during combustion events when acrolein monitoring is desired, a method to eliminate or account for the interference is necessary. Aerodyne has developed a method to eliminate the ethylene interference by means of a chemical scrubber of acrolein. The scrubber allows the elimination of the interference via spectral background subtraction. The idea is that if a combination of acrolein and ethylene is spectrally measured and then compared to a measurement with acrolein removed, the amount of acrolein can be determined. An appropriate room temperature scrubber was successfully tested and deployed. In combination with the high resolution of the cw QC laser, Aerodyne will be able to sensitively monitor acrolein in the presence of ethylene.
Acrolein has infrared absorptions in the 958 cm-1 region. Because a laser for acrolein monitoring could not be delivered to Aerodyne during the period of the project, laboratory tests of the instrument using a RT-cw QCL for formaldehyde (HCHO) at 1770 cm-1 were conducted. Formaldehyde, a hazardous air pollutant, provided an excellent proxy species for our experiments. This trace species and the RT-cw QCL were used to evaluate the instrument performance and estimate the sensitivity that will be achieved when an acrolein laser is obtained in the near future.
Aerodyne achieved a detection limit (instrument noise) of 0.38 ppb HCHO in 1 second with the new compact cw QCL instrument. With 100 seconds of averaging, a sensitivity of 0.05 ppb was obtained. This is equivalent to the sensitivity achieved previously by Aerodyne in a cryogenic system that had a pulsed QC laser and a liquid nitrogen cooled detector [Herndon, et al., 2007].
Optical interference fringes are a major contributor to the instrument noise in a cw laser instrument. A detailed analysis of the fringes and their impact in the compact system was conducted. Several sources of the fringes were identified, including high frequency fringes that come from the multipass cell. A piezo was mounted on a multipass cell mirror to eliminate such fringes. Continued tests of the interference fringes will further improve the sensitivity and stability of the instrument.
Conclusions:
Aerodyne can use the excellent results of the formaldehyde measurements with the compact RT-cw QCL to estimate the acrolein sensitivity the instrument can be expected to acheive. Aerodyne estimates that the HCHO sensitivity of 0.38 ppb in 1 sec corresponds to the sensitivity to acrolein of 1.6 ppb in 1 second. The HCHO sensitivity of 0.05 ppb with averaging (100 sec) corresponds to acrolein sensitivity of 0.21 ppb in 100 seconds. Instrumentation with these detection limits will be important to allow researchers to both directly measure source emissions and monitor ambient levels of acrolein in the atmosphere.
There exists a need for commercially available air quality instrumentation for acrolein and other toxic air pollutants for routine air quality monitoring in urban areas for health effect assessment, and at industrial sites for measuring direct emissions of these gases from manufacturing facilities. Acrolein is produced by combustion in internal combustion engines, vehicle exhaust, aircraft emissions, as a by-product of petroleum refining, and during industrial processing of wood and paper products. The diversity of sources and the relatively high reactivity of acrolein require a highly sensitive, easily portable, and fast response measurement technique. The infrared laser detection technique has wide commercial applications both for routine air quality monitoring and for source assessment of hazardous air pollutants.
References:
U.S. EPA, Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Method TO-11A, Center for Environmental Research Information, Office of Research and Development, U.S. EPA, Cincinnati, OH, 1999.
Herndon, S.C., M. S. Zahniser, D. D. Nelson Jr., J. Shorter, J. B. McManus, R. Jiménez, C. Warneke, and J.A.d. Gouw, Airborne measurements of HCHO and HCOOH during the New England Air Quality Study 2004 using a pulsed quantum cascade laser spectrometer, J. Geophys. Res., 112 (D10), D10S03, 2007.
Ho, S.S., and J.Z. Yu, Feasibility of collection and analysis of airborne carbonyls by on-sorbent derivatization and thermal desorption, Anal. Chem., 74, 1232-1240, 2002.
Ho, S.S., and J.Z. Yu, Determination of airborne carbonyls: Comparison of a thermal desorption/GC method with the standard DNPH/HPLC method, Environ. Sci. Technol., 38, 862-870, 2004.
Supplemental Keywords:
small business, SBIR, EPA, hazardous air pollutant, air emissions, air pollution, air quality monitoring, emissions monitoring, aldehydes, acrolein measurement, acrolein monitor, air, scientific discipline, air pollutants, air toxics, environmental monitoring, combustion technology, hazardous air pollutants (HAPs), aerosol particles, acrolein, environmental effects, atmospheric particulate matter, emission detection, novel quantum cascade laser spectrometer, room temperature cw QCL , Scientific Discipline, Air, air toxics, Air Pollutants, Environmental Monitoring, atmospheric particulate matter, aerosol particles, aldehydes, Acrolein, combustion technology, hazardous air pollutants (HAPs)SBIR Phase I:
Acrolein Monitor Using Quantum Cascade Laser Infrared Adsorption | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.