Using aerosol photometry to monitor the coarse and the fine fraction of work place and urban aerosols

When using light scattering (photometry) to monitor the aerosol mass concentration one has to take into account the fact that the scattering signal depends not only on the concentration but also on the size distribution and the optical properties of the aerosol material. The (photometric) sensitivity per aerosol mass is maximum for particles with sizes of the order of the wavelength of the incident light while showing a dhigh3subp-behavior to the left, respectively a dhighminus1subp-behavior to the right of the peak. By properly choosing the scattering angle and the wavelength it is possible to match the sensitivity curve approximately with the probability curve for particle deposition in the alveolar region of the lung. This makes aerosol photometry suitable for health related monitoring for the respirable fraction of the airborne particulate material (Armbruster et al., 1984). Excellent time resolution is combined with a low detection limit. There are several instrument commercially available using this measuring technique (TM digital, mini-RAM). In many cases the coarse fractions such as the thoracic and extrathoracic fractions are also of interest. To monitor these fractions as well, besides the fine dust, one has to take measures to compensate for the lower scattering efficiency per mass for the coarse particles. We have extended the use of aerosol photometry to simultaneously monitor the fine and the coarse fraction of the airborne dust.