Determination of bacterial aerosol spectral cross-sections

In a continuing series of experiments designed to determine the spectral extinction cross-section of bacterial aerosols, a White cell transmissometer was constructed to obtain stable, long path length measurements. Laser transmittance at different aerosol concentrations allows calculation of the extinction cross-sections. Using three lasers, a HeNe at 543run, a diode pumped solid state at 1.064mum, and a fiber laser at 1.558mum, the data on the spectral cross section of Bacillus globigi (BG) was extended into the NIR. The extinction cross-section was estimated to be 2.58 x 10(-9) cm(2) at 543mn wavelength during the 2003 measurements, which is consistent with previous measurements at this wavelength. In the NIR, the cross section of BG was determined to be 2.71 x 10(-8) cm(2) and 2.32 x 10(-8) cm(2) at 1.064 and 1.558mum, respectively. To validate the measurements, Mie calculations were used to continuously represent the extinction and backscatter cross-sections from the UV to NIR. The efforts described herein are intended to explore the various optical scatter features that may allow discrimination of biological pathogens from naturally occurring aerosol constituents such as pollen, dust, etc.