Laboratory evaluation of the scattering matrix of ragweed, ash, birch and pine pollens towards pollen classification

Pollens are nowadays recognized as one of the main atmospheric particles affecting public human health as well as the Earth's climate. In this context, an important issue concerns our ability to detect and differentiate among the existing pollen taxa. In this paper, the potential differences that may exist in light scattering by four of the most common pollen taxa, namely ragweed, birch, pine and ash, are analysed in the framework of the scattering matrix formalism at two wavelengths simultaneously (532 and 1064 nm). Interestingly, our laboratory experimental error bars are precise enough to show that these four pollens, when embedded in ambient air, exhibit different spectral and polarimetric light scattering characteristics, in the form of ten scattering matrix elements (five per wavelength), which allow identifying each separately. To end with, a simpler light scattering criterion is proposed for classifying among the four considered pollens by performing a principal component (PC) analysis, that still accounts for more than 99 % of the observed variance. We thus believe this work may open new insights for future atmospheric pollen detection.