Final Report: Remote Sensing of Automobile Emissions Using Raman LIDAREPA Contract Number: 68D00262
Title: Remote Sensing of Automobile Emissions Using Raman LIDAR
Investigators: Karger, Arieh
Small Business: Radiation Monitoring Devices Inc.
Project Period: September 1, 2000 through March 1, 2001
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2000) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:Automobile emissions control has become a very important cornerstone of the Clean Air Act of 1990. Automobile emissions standards and automobile emissions testing continue to have a significant positive impact on metropolitan air quality. In order to continue improving air quality, emission standards and testing have become more stringent. The Clean Air Act of 1990 required the EPA to develop standards for new automobiles and certification testing of older automobiles. Most states currently employ annual (or bi-annual) automobile emissions testing, and a significant fraction have proceeded to enhanced emissions testing. The EPA requires on-road monitoring of operating vehicles to be an integral part of an enhanced emissions testing program. The ultimate goal of on-road monitoring is to identify automobiles that emit excess pollution so that corrective action may be taken. While privacy and legal concerns may constrain the use of remote sensing to achieve these goals, remote sensing of automobile emissions is currently being used by a number of states. Remote sensing is expected to improve the ability of states to monitor automobile emissions and result in significant cost reductions associated with "clean screening" programs, where low emitters are exempted from annual enhanced emissions inspections. The development of accurate remote sensing systems for automobile pollution monitoring is expected to be an important factor for improving the air quality of major metropolitan areas.
While there are a number of techniques available for remote sensing of automobile emissions, many of these techniques have significant performance limitations. Remote sensing systems based upon Light Detection and Ranging (LIDAR) are very promising for standoff detection of various pollution gasses. Most LIDAR systems have been developed for long range (> 1 km) monitoring to measure atmospheric variations of pollution. While the ability to remotely probe over great distances is important, these systems are usually expensive and cumbersome. By adapting these LIDAR techniques to short range applications (~10 m), significant cost and size savings will be realized, as well as improved detection sensitivity. The inherent advantage of the proposed Raman LIDAR system is that the transmitter and receiver can be co-located, eliminating the need for remotely locating the receiver or retro-reflector. This greatly simplifies the placement and set up of the remote emissions monitor. In addition, Raman LIDAR is self-calibrating to atmospheric oxygen and nitrogen, eliminating requirements for periodic calibration with test gasses. Finally, the system can determine the concentration of emission gasses as a function of range, enabling the system to localize the source of the emissions across a multi-lane highway. In Phase I of this SBIR program, we have demonstrated feasibility and completed the preliminary design for a functional prototype automobile emissions monitoring UV Raman LIDAR that will be produced in Phase II.
To achieve sufficient sensitivity for automobile pollution monitoring, the UV Raman LIDAR system must incorporate a high efficiency optical collection system and spectral analysis system. Radiation Monitoring Devices, Inc. (RMD) has completed the preliminary design of this optical receiver system, which has been optimized by an optical design consultant using state-of-the-art optical design software tools. RMD has also demonstrated a high efficiency linear avalanche photodiode detector (APD) array, which will be incorporated into the system to provide high efficiency detection of the spectrally resolved Raman return signal. The linear APD array geometry will be matched to the spectrometer output to optimize the system sensitivity and wavelength resolution. In Phase I, RMD also performed laboratory UV Raman LIDAR experiments to demonstrate that UV Raman LIDAR is very promising for remote sensing of automobile emissions.
This report summarizes the progress RMD has made on the following tasks delineated for this Phase I SBIR: 1) System analysis to determine the performance characteristics required for the short Range UV Raman LIDAR; 2) Laboratory demonstration of UV Raman LIDAR confirming the sensitivity estimates in the system analysis; and 3) Preliminary design of the optical system for the Phase II prototype. RMD has successfully completed all of the Phase I tasks and is confident that prototype development during Phase II will lead to a commercial remote emissions monitor using UV Raman LIDAR.
Summary/Accomplishments (Outputs/Outcomes):The system analysis indicates that UV Raman LIDAR is an excellent candidate for remote sensing of automobile emissions. The variables that were analyzed include excitation wavelength and energy, Raman scattering cross section, receiver aperture, and range to automobile. The analysis indicates that, for reasonable design assumptions, the system will be capable of achieving a detection limit of 1-100 ppm for most gasses of interest. Some gasses, such as SO2 will achieve a detection limit better than 1 ppb due to an enhanced Raman cross section. These detection limits are sufficient for on-road emissions testing to detect low emitters for clean screening applications as well as early detection of gross emitters to expedite repair of failed emissions systems.
The laboratory experiments included the design and construction of a custom Raman LIDAR test chamber. Various test gasses were introduced into the Raman LIDAR test chamber and the Raman backscatter returns were analyzed as a function of wavelength and gas pressure. The results indicate an excellent ability to identify and quantify the test species. By analyzing the sensitivity of these Phase I laboratory experiments, we estimate that the Compact UV Raman LIDAR system will be capable of achieving better than 120 parts per million (PPM) sensitivity for NO, 40 ppm for N2 and CO, and 10 ppm for NO2 and hydrocarbons.
In addition to the laboratory experiments, we developed the preliminary optical design for the Phase II prototype optical receiver. This design takes advantage of RMD's unique large area linear APD detector arrays to maximize the detection efficiency for the Raman backscatter return. The Raman return is spectrally resolved with ~1 nm resolution, which is sufficient to uniquely identify the typical pollution species from an automobile exhaust. This preliminary design will be implement in the Phase II prototype to demonstrate the full capabilities of the UV Raman LIDAR for automobile emissions monitoring.
Finally, RMD completed the Phase I commercialization analysis. Foresight Science and Technology, Inc. (FST) found that RMD's unique approach to automobile emissions monitoring is an attractive solution and could be expected to perform well in the commercial marketplace. In addition to FST, RMD is working with the Massachusetts STrategic Envirotechnology Partnership (STEP) to facilitate commercialization of the automobile emissions LIDAR. RMD participated in a Commercialization Partnering Assistance roundtable organized by STEP to assist in the commercialization of the UV Raman LIDAR for automobile emissions monitoring. The participants in the roundtable were very excited about the potential of UV Raman LIDAR for automobile emissions monitoring. We believe that the development of the Compact UV Raman LIDAR prototype in Phase II will result in the successful commercialization of the automobile emissions monitor.