Photoacoustic sensor for carbon aerosols

To realize a small-sized and mobile sensor for elemental carbon, we used a laser diode as the light source for our spectrophone. The advantages of a laser diode compared with other laser types in the Vis and NIR are the emission wavelength of 780 nm, avoiding signal perturbations by trace gases (NO2, H2O), and the electronic modulation of the light intensity instead of modulation by a mechanical chopper, resulting in a decreased background signal and a simplified spectro-phone set-up. The combination of a NIR-emitting laser diode radiation source and the photoacoustic technique result in a small-sized and mobile sensor for particulate carbon in the atmosphere. The use of a high-power laser diode is expected to lower the detection limit to 1 μg EC m3 or less, corresponding to ambient mass concentrations of particulate carbon. The NIR emission wave-length of the laser diode avoids signal perturbations by absorbing trace gases. So this sensor principle will become a powerful tool as an environmental measurement technique for particulate carbon as long as interferent dust particles are absent.