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PARTICULATE MATTER MEASUREMENTS USING OPEN-PATH FOURIER TRANSFORM INFRARED SPECTROSCOPY
Hashmonay, R. A. AND D B. Harris*. PARTICULATE MATTER MEASUREMENTS USING OPEN-PATH FOURIER TRANSFORM INFRARED SPECTROSCOPY. Presented at AWMA Annual Meeting, Orlando, Florida, 6/24-28/01.
Open-path Fourier transform infrared (OP-FT1R) spectroscopy is an accepted technology for measuring gaseous air contaminants. OP-FT1R absorbance spectra acquired during changing aerosols conditions reveal related changes in very broad baseline features. Usually, this shearing of a spectrum's baseline is viewed as undersirable because it interferes with quantifying gases. However, the paper shows that this wavelength-dependent absorbance can be used to measure particulate matter (PM). It describes a developed inversion algoithm for retrieving the size distribution of the PM in the beam path. It gives preliminary results from OP-FT1R measurements conducted downwind from an active dirt road. Using the developed inversion algorithm and measured optical properties, the calculated extinction spectra were fitted to the measured extinction, using the Mie theory for spherical particles. Time series data reveal significant rapid shifts in size distribution of the PM in the OP-FT1R. Results indicate that size distribution parameters may be retrived from OP-FT1R spectra acquired over an open optical path. The suggested method may provide real-time concentrations of gaseous and PM contaminants simultaneously. Emission flux estimates of PM may be generated for near-ground-level (roads) and area sources when seveal beam paths are developed downwind.