Spectroscopic remote sensing exhaust emission monitoring system

• US 6,455,851 B1
• Filed: 04/11/2000
• Issued: 09/24/2002
• Est. Priority Date: 03/28/2000
• Status: Expired due to Fees

• Current Assignee: Harry C. Lord III
• Original Assignee: Air Instruments & Measurements, Inc.
• Inventors: Baum, Marc M., Lord, Harry C.
• Primary Examiner(s): Anderson, Bruce
• Assistant Examiner(s): Wells, Nikita
• Application Number:
  US09/547,154
• Time in Patent Office: 896 Days
• Field of Search: 250/338.5, 250/339.13, 250/343, 250/365, 250/504.R
• US Class Current: 250/338.5
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A spectroscopic IR and UV-vis absorption remote exhaust emission monitoring system and sensing instrument for non-invasive, multicomponent analysis of the exhaust plume emitted by in-use vehicles. The concentration of CO, CO_2, HC, NO, N₂O, C₂H₂, NH₃, SO₂, Aromatic hydrocarbons, aldehydes, HONO, NO₂, and dust, among others and in any combination there-of, in such a mixture can be determined in real-time, or via post-processing of stored spectral data. The sensor employs an IR and a UV-vis sources, and the physically offset, collimated beams traverse the probed air column, typically a roadway, a plurality of times, before returning to the instrument. Although the IR and UV-vis beams converge at the optics opposite the instrument, they are not coaxial and, thus, do not require an optical device (i.e., dichroic beam splitter) to separate them. The separate IR and UV-vis beams are focused on the slits of rapid spectrometers, where they are analyzed to yield wavelength-resolved spectra (i.e., graphs of digital signal intensity versus radiation wavelength). These spectrometers can either be rapid scanning dispersive devices, dispersive devices employing linear or two-dimensional detector arrays, or Fourier transform spectrometers. The graphs are converted into absorbance spectra and are subsequently processed with pattern recognition algorithms and a spectral reference database to afford analyte concentration.

Claims

1. A vehicle exhaust emission monitoring system comprising;

an IR radiation source;

a collimating optical system for collimating IR radiation from said IR source;

a UV radiation source;

a collimating optical system for collimating UV radiation from said UV source;

said IR radiation and UV radiation being physically spatially offset at the source;

a reflector mirror assembly on the opposite side of a path of travel of said vehicle from said IR and UV radiation;

said IR and UV radiation converging at said reflector mirror so that said IR and UV radiation makes multiple passes across said path;

optical assemblies receiving and calibrating said IR and UV radiation respectively;

IR and UV spectrometers receiving said IR and UV radiation respectively from said optical assemblies for generating wavelength resolved spectra; and

processing means for processing said wavelength resolved spectra from said IR and UV spectrometers to detect and measure an analyte of interest;

whereby a plurality of analytes can be detected and analyzed.

2. The system according to claim 1 in which said reflector mirror assembly includes;

a single spherical mirror on the opposite side of said path receiving said IR and UV radiation whereby said IR and UV radiation makes two passes across said path.

3. The system according to claim 2 in which said single spherical mirror comprises;

a single spherical mirror with adjustable and variable focal length on the opposite side of said path receiving said IR and UV radiation whereby said IR and UV radiation makes two passes across said path.

4. The system according to claim 1 in which said reflector mirror assembly includes;

a pair of reflector mirrors on the opposite side of said path and a third reflector mirror on the same side of said IR and UV sources receiving said IR and UV radiation whereby said IR and UV radiation makes two or more passes across said path.

5. The system according to claim 4 in which said reflecting mirrors are spherical mirrors.

6. The system according to claim 5 in which said optical assembly for receiving said IR and UV radiation comprise a sealed optical calibrating assembly for calibration and projecting said IR and UV radiation on an entrance slit of said respective spectrometer.

7. The system according to claim 5 in which said optical assembly includes a pair of Schwarzshield telescopes for each of said IR and UV radiation beams.

8. The system according to claim 4 in which said IR and UV spectrometers comprise;

a rapid scanning detector device having a grating mounted in a synchronous motor.

9. The system according to claim 8 in which said rapid scanning detector device is a plurality of rapid scanning detector devices.

10. The system according to claim 8 in which said IR and UV spectrometers comprise an FTIR and FTUV spectrometer respectively.

11. The system according to claim 4 in which said IR and UV spectrometers comprise a detector array.

12. The system according to claim 11 in which said detector array comprises at least 128 detectors optically interfaced to a grating.

13. The system according to claim 11 in which said detector array comprises a 2-D detector array comprised of at least 16×

16 pixels, interfaced to an optical means for separating broadband radiation into component wavelengths.

14. The system according to claim 1 in which said processing means comprises a PC, said PC applying the Beer-Lambert law to collected and stored dark spectra and sample spectra to provide an absorbance spectrum of a vehicle exhaust plume.

15. The system according to claim 1 in which said processing means comprises a PC, said PC processing the collected spectral data to linearly baseline the wavelength range corresponding to the absorption band of the analyte being measured;

and applying a pattern recognition algorithm to the spectral data using a spectrum of the measured analyte from a spectral database as a reference pattern.

16. The system according to claim 15 in which said algorithms include a singular value decomposition theorem and/or a neural network.

17. A method of monitoring vehicle exhaust emissions comprising;

projecting an IR beam from a source;

collimating said IR beam;

projecting a UV beam from a source;

collimating said UV beam;

spatially offsetting said IR beam and said UV beam from their source;

reflecting said IR beam and said UV beam from a mirror on an opposite side of the path of travel off said vehicle from said IR and UV sources, said IR beam and UV beam converging at said mirror so that said IR beam and UV beam make more than one pass across the path of said vehicle;

calibrating radiation received from said IR beam and UV beam with an optical assembly;

generating wavelength resolved spectra by IR and UV spectrometers from radiation received from said IR beam and UV beam;

processing said wavelength resolved spectra from said IR and UV spectrometers to measure an analyte of interest;

whereby a plurality of analytes can be detected and analyzed.

18. The system according to claim 17 including reflecting said IR beam and UV beam from a plurality of mirrors on the opposite side of said path of said vehicle and a reflective mirror on the same side as said IR and UV sources to produce two or more passes across said path.

19. The system according to claim 18 including calibrating said IR and UV radiation in optical assemblies that comprise sealed in-line calibration cells.

20. The system according to claim 17 in which said wavelength resolved spectra is generated by IR and UV-vis spectrometers.

21. The system according to claim 20 in which said processing comprises;

applying Beer-Lambert law to stored dark IR and UV spectra collected and sample spectra to provide an absorbance spectrum of said vehicle exhaust plume.

22. The system according to claim 20 in which said processing comprises;

applying a pattern recognition algorithm to an absorbance spectrum using a reference spectral database.

23. The system according to claim 22 in which said algorithm comprises;

applying a singular valve decomposition theorem and/or a neural network.

24. The system according to claim 20 in which said processing mans comprises;

linearly baselining an absorbance spectrum over the spectral range corresponding to an absorption pattern of an analyte of interest.