Grantee Research Project Results

Final Report: Compact, Continuous Monitoring for Volatile Organic Compounds

EPA Contract Number: 68D98133
Title: Compact, Continuous Monitoring for Volatile Organic Compounds
Investigators: Hovde, David Christian
Small Business: Southwest Sciences Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)

Summary/Accomplishments (Outputs/Outcomes):

This Phase I investigation explored spectroscopic methods for measuring trace concentrations of specific volatile organic compounds (VOCs). The goal of the research was to demonstrate an accurate method for measuring gaseous VOC concentrations in industrial settings using the same diode laser based technology which has been successfully applied to the detection of simpler molecules. The research program sought to determine the typical spectral features of VOCs, learn how to exploit these features to permit measurement of the concentration of particular VOCs, and devise data processing methods to maximize the information extracted from a spectrum. Specific tasks of the investigation included

1. Fundamental spectroscopy of selected VOCs using the high resolution Fourier transform instrument at the Ohio State University,

2. Near infrared diode laser spectroscopy of a model compound,

3. Digital processing of the laser spectra to extract estimates of the concentration of VOCs present.

These tasks were all successfully completed. The fundamental spectroscopy task obtained spectra at high resolution over the wavelength range from 3,000 to 7,900 cm-1. This permitted the strength and shape of the spectroscopic features to be evaluated. Every compound has a region of relatively strong absorption.

A rapid laser-based technique for measuring VOC concentration was demonstrated. Based on wavelength modulation, the technique was easily implemented using commercial off the shelf electronics. This technique was shown to have a sensitivity for the model compound of at least 12 parts per million and likely much better. Improvements to achieve still lower detection limits are outlined. The magnitude of the signal was accurately predicted from the Fourier transform spectrum. This gives confidence that the other compounds can be measured with their expected sensitivities.

An algorithm was invented which deals with the most common source of error in diode laser measurements within the framework of least squares theory. As proof of the effectiveness of the new algorithm, the stability of a laser measurement was shown to increase, resulting in longer useful signal averaging times and at least 10% lower noise levels.

This VOC research has broad applications in industrial measurements of VOCs as toxic gases at chemical plants, as pollutants from smokestacks, and in process gas control applications. The novel data processing algorithm has applications to small molecule detection as well.

Supplemental Keywords:

Air, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Economic, Social, & Behavioral Science Research Program, Toxics, HAPS, Engineering, Chemistry, & Physics, Analytical Chemistry, Monitoring/Modeling, Market mechanisms, Environmental Engineering, Benzene (including benzene from gasoline), analyzer, measurement, field portable systems, detect, cost effective, remediation, chemical detection techniques, field monitoring, optical detectors, VOCs