Gas and Particulate Concentration Measurements and Standards

The objective is to develop and demonstrate accurate and robust measurement approaches that will establish optical absorption line intensities intrinsic to the species of interest as gas concentration _standards to replace current artifact standards for low concentrations and toxic and reactive gases. Also to develop a suite of reproducible carbon-based particulate matter (PM) reference materials with properties closely approximating that of natural PM. Finally, to provide a benchmark data set correlating liquid-phase fuels and combustion characteristics (droplet/particle characteristics/dynamics, chemistry) with that of the PM material (morphology, thermo-optical properties). Provide data for droplet-laden, homogeneous turbulent flow around obstacles for validation of fire suppression models.

New applications for gas standards demand high accuracy measurements of relatively low concentrations for reactive and non-reactive gas mixtures that exceed the capabilities of most currently used technologies. Therefore new approaches must be developed to meet these needs. This project's research efforts focus upon the development of accurate optical line intensity measurements as a basis to realize and disseminate primary gas measurement standards. The precise spectroscopic measurements of cavity ring down spectroscopy are used in conjunction with low-uncertainty methods of sample preparation to combine measurements of line shape and absolute number density to determine line intensity for pertinent absorption lines and bands. This approach yields absolute measurements of absorption line intensities for a variety of low-molecular weight target analytes such as CH4, H2O, NOx, O3 and NH3.

Federal and State agencies are coordinating effort to improve the understanding of airborne PM and its effects upon human health. An essential element in advancing the atmospheric science of fine particles is the ability to make unequivocal measurements of the physical and chemical properties of the particulate matter. Significant uncertainty exists regarding the quality of existing measurements, and how well the data sets represent the actual PM source signatures. Currently well-characterized PM standards do not exist. Three types of PM reference materials will facilitate measurement traceability and improved interlaboratory reproducibility:

• Pedigreed PM (i.e., non-complex PM with clear traceability to the SI)
• Simulated PM (i.e., blended mixtures of non-complex PM materials to resemble real PM)
• Real PM (serving as measurement benchmarks).

Future Plans:

• Develop and customize CRDS for probing CH 4 in the near-infrared.
• Intercompare gravimetrically determined gas concentration standards with intrinsic (optical) gas standards.

Quantitative cavity ring-down spectroscopy (CRDS) and absorption line intensity assignment

• Completed a series of absolute line intensity measurements (relative uncertainties < 1 %) of H2O linked to NIST primary standards of humidity generation using the frequency-locked CRDS system.
• Industrial Interaction – We guided the experimental design and interpretation of industrial CRDS measurements of H 2 O in a suite of semiconductor process gases. This study quantified the effect of pressure broadening (by the various host gases) on measurement sensitivity.

Particulates

• Identified chemical composition of soot formed within a swirl-stabilized, n-heptane spray flame, used Soxhlet chemical extractions to separate chemical species of interest, including PAHs from the soot.
• Measured the absorption coefficient of laboratory air particles and combustion-generated soot over a range of temperatures. Determined the effect of carbon shape and size on its absorption characteristics.
• Completed a benchmark data set on the transport of liquid fire suppressants around obstacles. Sandia is using these to validate the Vulcan fire physics code for spray-clutter interactive environments.