Finnish Meteorological Institute (FMI) has begun using three lidar instruments to retrieve the polarization value (a shape-relevant parameter) and the Ångström exponent (a size-relevant parameter) required for the determination of pollen presence.
This has helped the organization characterize the vertical distribution and optical properties of birch and pine pollen over the rural environment in Vehmasmäki, a village in Kuopio, Finland. Pollen release in the northern hemisphere is well-documented, yet little is known about its vertical distribution and optical properties.
The three ground-based lidars – namely a multi-wavelength PollyXT lidar, a Vaisala CL61 ceilometer and a Halo Photonics StreamLine Pro Doppler lidar – operate at different wavelengths, enabling the optical characterization at four wavelengths (355nm, 532nm, 910nm and 1565nm). This multi-wavelength information can be used as the unique signature for each pollen type.
Together with pollen surface observations from a Hirst-type spore sampler and in-situ aerosol observations, the researchers found that the amount of pollen in the aerosol mixture is decisive to the observed lidar optical properties.
Furthermore, given the low concentration of pollen in the air, the inclusion of the longer wavelengths was found to be beneficial due to their sensitivity to trace large aerosol particles such as pollen.
The organization pointed out that accurate pollen representation is essential for minimizing allergy-related symptoms. Lidar observations can improve pollen forecasts, serving as a validation tool or through the assimilation of the lidar observations in aerosol dispersion models of pollen.
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