Sensitivity study of bio-aerosol cross-sections

摘要

There is wide variability in measured optical cross-sections for bio-aerosols. This variability may be due to a variety of causes, such as multiple scatter, particle agglomeration, etc. There are wide variations in numerically predicted cross-sections as well. In this case, the variability may be due to uncertainties in particle size distributions and complex refractive indices. Another source of variability in the numerical predictions that places them at odds with measured cross-sections is unrealistic assumptions about shape. For example, it is well known that spheres of a given volume are maximally efficient in backscatter. Thus, such an assumption produces unrealistically high backscatter cross-section estimates. In an attempt to elucidate some of the variability in measured and calculated data, we explore the sensitivity to the various parameters affecting these cross-sections. We explore the effects from the near into the far IR, of variations in particle size distribution, refractive index, and shape. Refractive index data are from the literature as well as our own laboratory. Numerical calculations are made using T-matrix algorithms for randomly oriented particles. Calculated results are compared with experimental measurements from the literature and with measurements in our own laboratory. Results of this sensitivity study are important in any remote measurement system designed to discriminate between particular bio-aerosol species and ambient aerosols.