Extractive sampling system and method for measuring one or more molecular species

Abstract

A non-contact, extractive sampling system and method is provided for measuring the exhaust gas composition and fine particle composition of exhaust emissions of various types of vehicles under actual operating conditions. A portion (or sample) of an exhaust plume of a vehicle is pulled or extracted through an extraction sampling tube, via a vacuum pump, to a remote trace gas detection system where the concentration of one or more constituents present in the sample of exhaust plume may be measured. In this regard, the invention enables vehicle emissions measurements to be made at a location remote from roadway, rather than using known, “cross-path” remote emissions sensing systems.

1 . A system for measuring the concentration of one or more constituents present in an exhaust plume of a vehicle traveling on a roadway, comprising:
 a trace gas detection system, located remotely from the roadway, including a measurement cell;   a sampling tube having a first end that is positioned in the roadway, and a second end that interfaces with the measurement cell of the trace gas detection system; and   a vacuum pump configured to draw air away from the roadway to the measurement cell of the trace gas detection system at a predetermined flow rate, through the sampling tube, such that air including a sample of an exhaust plume from a passing vehicle may be provided to the measurement cell so the concentration of one or more constituents present in the exhaust plume sample may be measured.   
   
   
       2 . The system of  claim 1 , wherein the first end of the sampling tube is positioned approximately in the center of a vehicle travel lane on the roadway. 
   
   
       3 . The system of  claim 1 , wherein the sampling tube comprises an inner tube disposed within a protective outer tube. 
   
   
       4 . The system of  claim 3 , wherein the protective outer tube is fabricated from at least one of copper or stainless steel. 
   
   
       5 . The system of  claim 1 , wherein a portion of the sampling tube on the surface of the roadway is secured to the surface of the roadway to maintain it in a fixed position. 
   
   
       6 . The system of  claim 1 , wherein the predetermined flow rate is approximately 5.0 standard liters per minute. 
   
   
       7 . The system of  claim 1 , wherein the pressure in the sampling tube decreases over the length of the sampling tube from the first end positioned on the roadway to the second end that interfaces with the measurement cell of the trace gas detection system. 
   
   
       8 . The system of  claim 1 , wherein the pressure in the sampling tube decreases over the length of the sampling tube from atmospheric pressure at the first end to approximately 50 torr at the second end that interfaces with the measurement cell of the trace gas detection system. 
   
   
       9 . The system of  claim 1 , wherein the trace gas detection system comprises a mass spectrometer. 
   
   
       10 . The system of  claim 1 , wherein the trace gas detection system comprises a visible/ultraviolet absorption spectrometer. 
   
   
       11 . The system of  claim 1 , wherein the trace gas detection system comprises an infrared absorption spectrometer. 
   
   
       12 . The system of  claim 1 , wherein the trace gas detection system comprises a Quantum Cascade laser spectrometer, and further comprises a source and detector. 
   
   
       13 . The system of  claim 12 , wherein the source comprises a thermoelectrically cooled mid-infrared quantum cascade laser. 
   
   
       14 . The system of  claim 12 , wherein the detector comprises a thermoelectrically cooled mid-infrared detector. 
   
   
       15 . The system of  claim 12 , wherein the measurement cell comprises an astigmatic multipass absorption cell. 
   
   
       16 . The system of  claim 1 , wherein emissions from a plurality of vehicles are measured over a predetermined period of time to provide a representation of emissions attributable to general traffic. 
   
   
       17 . The system of  claim 1 , wherein individual exhaust samples are associated with individual vehicles. 
   
   
       18 . The system of  claim 17 , further comprising an imaging unit located proximate to the roadway to record images of passing vehicles for identification purposes. 
   
   
       19 . The system of  claim 18 , further comprising a computer in operative communication with the imaging unit and the trace gas detection system, wherein the computer correlates vehicle identification information with measured emissions information.