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K. Kato
[Bunseki Kagaku, Vol.43, No.4, pp.317-323, 1994]
This study was aimed at developing a real-time analysis method that is selective toward elemental carbon particles (EC) in the air. Although, suspended particles in the atmosphere consist of various substances, EC contained in diesel exhaust comprise a significant contribution. Because, EC adsorb many kinds of hazardous organic compounds. A near-infrared diode-laser photoacoustic technique using a longitudinal-mode resonant cell with a double-tube structure was applied to detect EC. The Q-factor of the cell was low (Q=10-16), and was less sensitive to any fluctuation of the temperature, pressure or humidity than the other resonant-mode cell such as a radial- or azimuthal-type resonant-mode cell with a high Q-factor. Figure shows the block diagram of the real time EC analyzer. A linear calibration curve was obtained within an EC concentration range of 0 to 10mg/m3; the sensitivity was 1.3mV/(mg/m3) with laser power of about 200mW. When the flow rate was 61/min the signal response settled within 10 min against any EC concentration change. Interference from NO2 in the atmosphere (less than 0.1ppm) was negligible with excitation by diode laser wavelength (lambda=806nm). The real time measurement of the EC concentration in room air can be performed without having to use an NO2 denuder.
