LII and one-wavelength Aethalometer measurements of
           particulate matter in different environments
       Silvana De Iuliis, Silvia Maffi, Francesca Migliorini, Giorgio Zizak
      CNR-IENI, Istituto per l’Energetica e le Interfasi, via Cozzi 53, 20125 Milano Italy,
                                     deiuliis@ieni.cnr.it



        Laser-Induced Incandescence (LII) technique is a powerful tool to measure
concentration and size of soot particulate. In this work LII measurements are
performed in different experimental conditions and compared with the ones derived
by using a commercial aethalometer. This instrument allows to obtain the on-time
concentration of optically absorbing aerosol particles by measuring the attenuation of
800 nm wavelength light through a quartz fiber filter. The filter is blackened over time
with the aerosol picked up inside the instrument at controlled flows. Measurements
are carried out with one second time-resolution. Absolute measurements in the ng/m3
range are derived for the particulate concentration. As for Laser-Induced
Incandescence, soot particles are sampled in a test cell, consisting of a pyrex tube.
The IR beam of a Nd:YAG laser (6 Hz, 200 mJ/cm2) is properly aligned within the
tube. The LII signal is detected at two wavelengths (530 nm and 700 nm) with PMT
modules coupled with interference filters. A fast digital oscilloscope, triggered by the
laser Q-switch pulse, is used for data acquisition and storage.
        The two sets of measurements are carried out at the exhaust of a soot
generator (fuelled by methane) and of a diesel engine as well as in ambient air
conditions (office and laboratories). In this way, a wide range of soot load and
particulate of different nature are investigated.




      Fig. 1: LII peak (left) and aethalometer measurements (right) versus time.

As an example, in Fig. 1 measurements carried out in ambient air are shown versus
time. Open symbols refer to the values of the LII peak at 500 nm wavelength
collected about every 10 minutes. The concentration values obtained with the
aethalometer are reported in closed symbols. The two sets of measurements are
quite well overlapped confirming that the two techniques are sensitive to the same
soot particulate and that the developed LII apparatus exhibits the high sensitivity
necessary for environmental measurements.




              5th international workshop on Laser-Induced Incandescence
               May 9-11, 2012, Palais des Congrès, Le Touquet, France