March 19, 2012

MEMORANDUM

SUBJECT: Data from the Evaluation of Instruments that Measure Nitrous Oxide (N 2 O)

FROM: Chris Laroo, Environmental Scientist

Assessment and Standards Division

TO: Docket EPA-HQ-OAR-2010-0799

This memorandum and attached file, “N 2 O Instrument Evaluation” shows the results of EPA’s evaluation of 4 technologies for N 2 O measurement, conducted during the fall of 2011 and winter of 2012. These technologies are the Gas Chroma tograph Electron Captur e Detector (GC-ECD), Fourier Transform Infrared Spectrometer (FTIR), Non-Dispersive Infrared (NDIR) analyzer, the Quantum Cascade Laser (QCL) analyzer, and scanning laser analyzer. These five technologies were evaluated for their accuracy in measuring light-duty vehicle N 2 O emissions at the dilute exhaust gas levels expected in meeting the 0.01 gram/mile N 2 O standard. This includes expected interference gas dilute exhaust concentrations of H 2 O in the 0 to 2% range, CO in the 80 to 300 ppm range, CO 2 in the 0.7% to 2% range, and CH 4 in the 20 to 24 ppm range (where applicable). The target range for N 2 O in dilute exhaust gas ranged from 400 to 800 ppb, which is within the range of dilute exhaust gas concentrations expected for a vehicle complying with the light-duty

vehicle N 2 O emission standard.

GC-ECD The results indicate that the GC-ECD continues to be a robust, accurate measurement method for

low level N 2 O analysis.

FTIR The results show that the FTIR can be prone to high bias due to interference from CO and CO 2 , however steps can be taken (like increasing the gas cell size and path length) to minimize the

interference contribution.

NDIR While improvements have been made to the NDIR, the instrument evaluated was prone to interference when the interference gas concentrations strayed from the concentration at which the interference correction coefficient was generated. Thus interference could be controlled within a given range of CO, CO 2 , and N 2 O concentrations; but care must be taken ensure

accurate measurement.

QCL The QCL is the most recently developed instrument. Evaluation of the instrument shows that it is not susceptible to interference from CO, CO 2 , or water. The instrument has excellent low level accuracy and results from measurement with this instrument should be consideredcomparable to that from a GC-ECD. The quad gas version of this bench that measures NO, NO 2 , N 2 O, and NH 3 is currently available for purchase. The single gas (N 2 O only) versions of the

instruments that we evaluated from two different manufactures have just been brought to market. Both manufacturer’s instrument are available for purchase. In both cases the single gas N 2 O bench is currently available for evaluation from each of the manufacturers.

Scanning Laser The scanning laser spectrometer has also been recently developed for measurement of N 2 O at sub-1 ppm concentrations. Evaluation of the instrument shows that it is not susceptible to interference from CO, CO 2 , CH 4 , or water. The instrument has excellent low level accuracy and results from measurement with this instrument should be considered comparable to that from a GC-ECD and QCL. This instrument is commercially available from one supplier.

Overall, the results indicate that methodologies are currently available to perform accurate low level (sub 1 ppm) measurement of N 2 O and that new instrumentation has been developed in response to EPA rulemakings to facilitate low level accurate measurement of N 2 O with no contribution from interference gasses. These instruments are currently available for purchase from the respective instrument suppliers.

Attachment: “N 2 O Instrument Evaluation”