Final Report: Nanocomposite Sensor Array for the Detection of Multiple Toxic Air Pollutants

EPA Contract Number: 68D01035
Title: Nanocomposite Sensor Array for the Detection of Multiple Toxic Air Pollutants
Investigators: Deininger, Debra J.
Small Business: Nanomaterials Research Corporation
EPA Contact:
Phase: I
Project Period: April 1, 2001 through September 1, 2001
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2001) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)

Description:

In today's environment there are continuing problems associated with the environmental effects of toxic materials in the air. In 1990, the Clean Air Act Amendments identified 188 toxic air pollutants, also known as hazardous air pollutants (HAPs), for their detrimental environmental effects. Since then, the integrated Urban Air Toxics Strategy has identified 33 HAPs as particularly threatening to public health in urban areas. The Urban Air Toxics Strategy HAPs are comprised of volatile organic compounds (VOCs), metals, aldehydes, and semivolatile organic compounds. Table 1 lists the VOCs that are identified as Urban Air Toxics by the U.S. Environmental Protection Agency (EPA).

Table 1. List of the Urban Air Toxic VOCs identified by EPA.

Acrylonitrile Benzene 1,3-butadiene
Carbon tetrachloride* Chloroform* 1,2-dibromomethane
1,3-dichloropropene 1,2-dichloropropane 1,2-dichloroethane (EDC)
Ethylene oxide Dichloromethane* 1,1,2,2-tetrachloroethane
Tetrachloroethylene (PCE) Trichloroethylene* (TCE) Vinyl chloride
* Compound was evaluated during the Phase I feasibility trial.

This concern over the environmental and health risks associated with the emission of VOCs from various sources has led to a pressing need for affordable and reliable ways to detect and quantify the presence of these gases at the point of release. A lower cost, reliable method of detecting these emissions could enable remediation efforts that will minimize their release into the atmosphere as well as the associated health and environmental risks. This low-cost detector also will aid in site remediation efforts by allowing workers to qualify and quantify VOC emissions in real time.

Summary/Accomplishments (Outputs/Outcomes):

The Phase I project has developed the basis of an array-style detector that is capable of qualitatively and quantitatively detecting small groups of VOCs. The detector array is based on nanocomposite chemiresistor sensors operated at cycled temperatures to create selectivity. The following achievements were noted by Nanomaterials Research, L.L.C., during the Phase I project.

Detection Limits. Detection limits of less than 5 ppm were achieved across a range of test conditions and challenge gases as listed below in Table 2. The detection limits were the concentration of challenge gas required for the signal to exceed three times the noise level.

Table 2. Challenge gases and their detection limits.

Challenge Gas Detection Limit
Carbon tetrachloride <1-2 ppm
Chloroform <1-2 ppm
Dichloromethane <1 ppm
Trichloroethylene <3 ppm

Response Time. The response time of the sensors was excellent, and in all cases the time to 90 percent of the final response was less than 1 minute. In many cases, the 90 percent response was less than 20 seconds.

Discrimination Among VOCs. Variations in sensor composition and temperature modulation were used to create selectivity by manipulating the sensor response to individual gases. A simple model then was developed to predict the response of the sensors when exposed to multiple gases simultaneously. This model will enable the quantification of multiple gases presented simultaneously using straightforward multivariate methods such as multiple regression, principal components analyses, or partial least squares. These efforts have laid the groundwork to develop a prototype array detector by the end of a Phase II effort.

Conclusions:

The results have shown that it is feasible to produce a simple and portable low-cost sensor array for the detection of multiple toxic air pollutants. The detector array is based on variations in sensor composition and operating method, and the data are manipulated using multivariate analyses. The resulting prototype product is envisioned as a portable instrument that is capable of quantitatively identifying small groups of VOCs for specific target applications.

Supplemental Keywords:

VOC, sensor array, chlorinated hydrocarbons, urban air toxics., RFA, Scientific Discipline, Air, Toxics, Ecosystem Protection/Environmental Exposure & Risk, air toxics, Chemistry, VOCs, Monitoring/Modeling, Environmental Monitoring, tropospheric ozone, Atmospheric Sciences, Environmental Engineering, air pollutants, stratospheric ozone, ambient air, detect, air pollution, Volatile Organic Compounds (VOCs), measurement methods , sensor