Abstract
Although suspended particles in the atmosphere consist of various substances, the elemental carbon particles (EC) contained in diesel exhaust comprise a significant contribution. This is because EC adsorb many kinds of hazardous compounds. This study was aimed at developing a real-time analysis method that is selective toward EC. 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=16.5), and was less sensitive to any fluctuation of the temperature, pressure or humidity than a radial- or azimuthal-type resonant-mode cell with a high Q-factor. A linear calibration curve was obtained within an EC concentration range of 0 to 10 mg/m3; the sensitivity was 1.3 mV/(mg/m3) with 222 mW laser power. 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 was negligible with excitation by the diode laser (λ=806 nm). Further, the EC concentration in room air can be measured without having to use an NO2 denuder.
