Grantee Research Project Results
Final Report: A Sensitive and Affordable Compact Ammonia Monitor
EPA Contract Number: EPD09039Title: A Sensitive and Affordable Compact Ammonia Monitor
Investigators: Shorter, Joanne H
Small Business: Aerodyne Research Inc.
EPA Contact: Richards, April
Phase: II
Project Period: March 1, 2009 through February 28, 2011
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2009) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Pollution
Description:
Emission of ammonia to the atmosphere is a major environmental concern and a potential health hazard. The accurate measurement of ammonia sources, however, is lacking and requires improved instrumentation. There is a need for high sensitivity, fast response, autonomous, and continuous ammonia instruments to monitor present emissions, quantify the effectiveness of control measures, and evaluate the effects of ammonia emissions on local and regional soils, groundwater, and atmospheric environments. The goal of this program was to meet this need through the development of a low cost and compact ammonia monitor based on a novel multipass cell.
At high levels such as found at animal feed lots, ammonia (NH3) is a health hazard. Even at low levels, however, it is both a health and an environment concern. Ammonia is a major source of PM2.5 particulates upon interaction with other compounds in the atmosphere. These particulates are a known hazard to human health and have therefore come to be regulated. The transport and subsequent deposition of ammonia means it can have local, regional, and global impact on the environment.
Europe and the United States have begun to regulate ammonia to address its direct and indirect environmental and health effects. As a result, there now is a need for improved instrumentation to study the impact of regulation on ammonia levels. The purpose of this project is to develop a lower cost yet highly sensitive, rapid response, robust, and portable instrument for autonomous real-time monitoring of ammonia emissions. The instrument will not require calibration gases or liquid nitrogen. The goal for sensitivity is to measure ammonia concentrations accurately to less than 1 part per billion by volume (ppbv) in a 1-second measurement, and to record data continuously at 1 Hz. A second major goal of this program is to achieve the desired high sensitivity at reduced cost.
The individual Phase II specific objectives were formulated to reach the overall goal of an affordable, compact, sensitive, cryogen-free ammonia monitor based on quantum cascade laser (QCL) technology. The four tasks of the project were: (1) optical module design, including the design of both an alternative lower cost multipass cell design and lower cost laser collection optics, and the detailed design of a new low cost optical module; (2) electronic module design, including development of low cost instrument temperature control, a data acquisition system, and a final electronics module design; (3) construction of a prototype QCL ammonia instrument; and (4) instrument testing. In these research tasks, Aerodyne Research focused on ways to make the instrument more affordable and compact while maintaining or improving the high sensitivity and fast response of the company's previous compact QCL instruments.
Summary/Accomplishments (Outputs/Outcomes):
Aerodyne Research successfully met the objectives of the SBIR Phase II program. The four tasks of the program were addressed culminating in the design, construction, and testing of a new prototype ammonia instrument.
The two main subtasks of the optical design were to investigate lower cost multipass cell and collection optics.
The purpose of a modified absorption cell design is to allow the development of a lower cost ammonia instrument, while maintaining high standards for sensitivity and accuracy. The high sensitivity requirement implies that the available path length should remain close to what it now is for an ARI AMAC-76, on the order of 76 meters [McManus, et al., 1995; McManus, 2007]. Also, high accuracy suggests that the cell path length be well defined, and that optical interference fringes should be minimal. Aerodyne Research has devised a novel proprietary design for a new multipass cell. Some key features of the cell include the following: the use of economical mirrors; high cell throughput compared to other cell configurations; a small output spot size maintained; and the overall spot pattern is well matched to round mirrors, so the volume between the mirrors is well filled. Aerodyne Research is exploring a patent application for the new cell design approach.
A major cost element of Aerodyne Research's instrument has been the reflecting objective to transform the diverging beam from the laser to a relatively narrow beam. The company has designed a new collection optics that is a hybrid optical element with both a low cost lens and mirrors. The design yields a good image quality without spherical aberrations typically seen at larger angles. This hybrid element is less costly than the reflecting objective presently used.
Aerodyne Research explored a third avenue related to the optical module to cut overall instrument cost and size. One component that the company targeted for possible elimination from the instrument is the recirculating bath. A Thermocube, a temperature controlled recirculator, is typically used to remove heat from the laser housing and to cool the infrared detector. Elimination of the Thermocube water circulator from the system will result in both size and cost reduction. The goal was to design a way to dissipate the heat generated by the laser housing and detector without using an expensive temperature controlled recirculating bath, possibly no recirculator at all. The elimination of the bath would result in significant size and cost savings.
In this project, Aerodyne Research demonstrated air cooled QCL operation. The company designed and tested a new laser housing with heat sink fins and a small fan to circulate air across the fan to help dissipate the heat. A small 10 micron air cooled Vigo detector was purchased and integrated in the instrument. The results showed excellent laser stability with air cooling. Aerodyne Research achieved a 1 sec precision of 0.18 ppb NH3 and a minimum precision of 0.017ppb NH3 with 200 sec averaging with the air cooled instrument. The company has demonstrated excellent performance of an entirely air cooled pulsed QCL instrument for sensitive ammonia measurements. No liquids were used in this system. The system has been running unattended for months.
Aerodyne Research has designed a simpler, lower cost electronics module. A new data acquisition configuration with lower cost National Instrument (NI) cards has been implemented. This has led to the cost reduction in the data acquisition boards of approximately 30 percent. It remains one of the company's goals to further modify the instrument’s electronic design to provide the same functionality with a single card (USB6251), for a total cost reduction with respect to the data acquisition boards of 60 percent. Additional cost-saving approaches were taken in other instrument components, including the pressure sensor.
Aerodyne Research has constructed a new compact cw QCL instrument and demonstrated the operation of a cw QCL with very high sensitivity NH3 detection without the need of the expensive, bulky Thermocube. The system performed excellently without thermal control on the liquid cooling for the laser housing. Precision levels of 0.048 ppb NH3 in 1 sec and 0.0095 ppb in 130 sec were achieved. The detector in this system did not use any liquid or fan cooling but was simply well heat sinked to the optical base, with excellent thermal stability. The implication of these results is that the large temperature controlled circulator can be replaced by a small, much less expensive water circulator.
Conclusions:
Aerodyne Research has designed and constructed a lower cost, compact, sensitive ammonia monitor based on QCL technology. Operation of an entirely air cooled pulsed laser system was demonstrated with 1 sec precision of 0.18 ppb NH3. The company also constructed and operated a cw QCL instrument with an unregulated temperature water circulator. A 1 sec precision of 0.048 ppb NH3 was achieved. Significant cost savings were realized and further future savings identified for construction of the instrument. Aerodyne Research expects that these savings will lead to further commercialization and sales of its compact instrument.
Supplemental Keywords:
environmental monitoring, emission detection, ammonia, novel multipass cell, air cooled instrument;SBIR Phase I:
A Sensitive and Affordable Compact Ammonia Monitor | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.