Grantee Research Project Results
Final Report: Development of an Improved Detector for Use With a Gas Chromatograph to Measure NO2 and PAN in the Atmosphere
EPA Contract Number: EPD08034Title: Development of an Improved Detector for Use With a Gas Chromatograph to Measure NO2 and PAN in the Atmosphere
Investigators: Fitz, Dennis R.
Small Business: Fitz Aerometric Technologies
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2008 through August 31, 2008
Project Amount: $66,885
RFA: Small Business Innovation Research (SBIR) - Phase I (2008) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Pollution
Description:
Although nitrogen dioxide (NO2) is a priority pollutant, the Federal Reference Method is based on the chemiluminescent measurement of nitric oxide (NO) with the assumption that NO2 is the difference between nitrogen oxides (NOx) reduced to NO with a converter and the NO originally in the sampled air. These converters also are effective in reducing a wide variety of nitrogenous species found in polluted atmospheres such as HNO3, HONO, and peroxyacetyl nitrate (PAN) and even NH3 at low efficiency. The presence of these nitrogenous compounds results in a positive bias when measuring NO2. Indeed, well-aged photochemical smog contains very little NO2 when the analyzer is measuring tens of ppb.
While this bias was well understood when the reference method was chosen, the availability and reliability of relatively low maintenance and low cost chemiluminescent analyzers were the determining factors in the choice. While wet chemical methods were available, they were complex, unreliable, and required highly trained personnel. The development of luminol-based chemiluminescent direct detection of NO2 was an improvement, but these analyzers were subject to interferences such as ozone and other oxidized nitrogenous species. Coupling these luminol detectors with gas chromatography resulted in specific detection of NO2 (and other nitrogenous species), but the complexity and reliability of these instruments precluded wide-spread adoption. A new detector has been developed specifically for the low flow rates of capillary gas chromatography and while it has many advantages, it still requires regular replacement of reagent. The objective of this research was to develop a luminol-based chemiluminescent gas chromatographic detector that is a sealed system that does not require a liquid reagent pump.
Several detectors were designed and one was constructed and evaluated in two gas chromatographic analyzers to measure NO2 concentrations. These included a prototype and an optimized prototype. Both of these analyzers were evaluated for reliability and calibration stability by performing day-long calibration span tests conducted over periods of many weeks.
Summary/Accomplishments (Outputs/Outcomes):
The prototype was shown to operate reliably without adding reagent or using a liquid reagent pump. In this design, it is the air carrier gas flow that circulates the liquid reagent. One of the problems with this prototype was that the pH of liquid reagent would gradually drop, resulting in calibration drift that was significant after several days to a week. A scrubber was used to eliminate CO2 from the air carrier gas to reduce the potential of CO2 dissolving in the liquid reagent and upsetting the pH of the buffered reagent. The concentrations of the components of the liquid reagent also were increased by an order of magnitude to promote long-term stability. This resulted in only a 50 percent drop in sensitivity.
In the optimized prototype, all of the gas chromatographic components were housed in a temperature-controlled environment in an attempt to reduce calibration variability. The luminol reagent reservoir also was made ten times larger to allow the reagent to perform longer. It has operated for over a month without any maintenance and has shown no significant calibration drift for nearly 2 weeks. A multi-point calibration has shown nearly perfect linearity and no significant intercept.
Conclusions:
The primary goals of this Phase I project have been met by the end of the contract period. The optimized prototype does not require either a reagent pump or the addition of a reagent. Both the original and optimized prototypes will undergo continuing long-term stability testing after the end of the contract period. The final prototype also will be equipped with an NO oxidizer to allow measurement of this species, which is required to be equivalent to the current reference method.
This research has lead to the development of an NO2 analyzer that is not only specific for this species but has the potential for adequate long-term stability and reliability. The use of components with RS232 outputs that can be directly connected to a PC simplifies the overall design and reduces the cost. It is anticipated that the costs to manufacture this instrument will be less than the existing ozone-chemiluminescent NO-NOx analyzers.
Fitz Aerometric Technologies plans to describe the results in both technical publications and conference presentations with the goal of building and selling the instruments to researchers. Favorable performance of these instruments will potentially generate increased licensing interest from commercial analyzer manufacturers.
Supplemental Keywords:
small business, SBIR, EPA, nitrogen dioxide, NO2, nitrogen dioxide detector, Federal Reference Method, air pollution, chemiluminescent measurement, polluted atmospheres, nitrogenous compounds, photochemical smog, chemiluminescent analyzers, luminal-based chemiluminescent gas chromatographic detector, effluent gas, chromatographic column, luminal reagent, peroxyacetyl nitrate, PAN, air monitoring, remote sensing, sustainable industry/business, scientific discipline, RFA, technology for sustainable environment, sustainable environment, environmental chemistry, gas chromatography, nitrogren oxides, NOx, air pollutants, air monitoring, air pollutant measurement, air quality measurement,, RFA, Scientific Discipline, Sustainable Industry/Business, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, environmental monitoring, remote sensing, air pollutants, nitrogren oxides (NOx)The 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.