Grantee Research Project Results

Final Report: A Real-Time, Sensitive and Affordable Fast-Response Elemental Carbon Monitor

EPA Contract Number: EPD11040
Title: A Real-Time, Sensitive and Affordable Fast-Response Elemental Carbon Monitor
Investigators: Berkhahn, Wolfgang
Small Business: EcoChem Analytics
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2011 through August 31, 2011
Project Amount: $79,022
RFA: Small Business Innovation Research (SBIR) - Phase I (2011) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air and Climate

Description:

The purpose of this research project was to design, manufacture, and test prototype aerosol pre-treatment devices to remove the organic carbon fraction from carbonaceous aerosols before entering the ionization chamber of the Photoelectric Aerosol Sensor (PAS). Specifically, the two pre-treatment devices tested were a Thermo-denuder and a Catalytic Stripper.

Summary/Accomplishments (Outputs/Outcomes):

EcoChem Analytics designed and manufactured two unique aerosol pre-treatment devices to remove the organic carbon fraction from carbonaceous aerosols. One device implements a thermal heating profile to remove volatile organic compounds. The other device includes a catalytic mesh that oxidizes the organic fraction. These devices were challenged with test aerosols from a PALAS carbon particle generator and a propane diffusion flame soot generator. The primary research findings are as follows: 

1. Two design configurations of the pre-treatment device were developed in this project. The initial design was based on a "vortex flow" configuration. This design offers maximum flow path within an extremely small volume. However, manufacturing difficulties associated with the catalytic stripper proved to be a challenging task for this configuration. Subsequently, EcoChem Analytics developed a simpler "S-shaped" flow path denuder with vertical placement of the catalytic stripper. This configuration provided a workable design for further experiments.
2. The PALAS carbon particle generator must be used with caution because it generates carbon particles in a "cold" environment primarily using a high voltage discharge between carbon electrodes. This process does not generate real-life carbon soot particles, which are usually produced at high temperatures in actual combustion flames. Combustion flame soot particles have a solid core that is absent in the PALAS generated particles. For subsequent experiments, EcoChem Analytics used a propane diffusion flame soot generator to produce real-life carbon aerosols.
3. Both pre-treatment devices (thermal and catalytic) with an appropriate thermal gradient flow path and catalytic stripper did not disturb the signal from the Photoelectric Aerosol Sensor. Readings taken before and after the pre-treatment devices indicated acceptable penetration efficiency. In addition, limited experiments with the pre-treatment devices showed promising condensed organic carbon removal capabilities.
4. The thermo-denuder has a consumable component (activated carbon fabric), while the catalytic stripper lasts for prolonged periods of time without recurring cost. Hence, the catalytic stripper is the preferred route for future development.

Conclusions:

Potential Applications

The aerosol pre-treatment device developed in this project is compact, rugged, and low-maintenance. It can be incorporated easily with the Photoelectric Aerosol Sensor to develop an elemental carbon analyzer that can be used for monitoring elemental carbon levels at traffic intersections and roadside monitoring. The sensitivity of the potential analyzer needs to be optimized so that it can be used for applications related to ambient air monitoring.