Recent study takes a step towards distinguishing pollen types in the air from lidar measurements
Kuva: Adobe StockPollen is a well-known health threat. Birch and spruce pollen are among the most abundant pollen types in Finland and especially birch pollen is known as one of the most allergenic pollen types in Europe.
We studied the optical properties of birch and spruce pollen in the atmosphere using lidar measurements during a campaign in the pollen season 2019 in Vehmasmäki (Kuopio), a rural measurement site of the Finnish Meteorological Institute.
Main instrument thereby was the multiwavelength Raman lidar PollyXT which provides depolarization ratio measurements at 2 wavelengths. The depolarization ratio can be used to estimate the shape of the observed particles. This is an essential quantity to discriminate pollen from other aerosols and further to identify different pollen types. We furthermore utilized measurements of a Halo Doppler lidar, which is usually used for wind and turbulence studies, to obtain the depolarization ratio at a third wavelength.
The measurements suggested a wavelength dependence of the depolarization ratio in the presence of spruce pollen with the highest depolarization ratio being at the intermediate wavelength. This can help to distinguish non-spherical pollen from other depolarizing (non-spherical) aerosol types such as dust. The classification of atmospheric pollen and their types using lidar measurements could improve the knowledge of the vertical pollen distribution. Until now, information about the vertical distribution of pollen is very rare, however it could significantly improve pollen transport and forecast models.
More information:
Stephanie Bohlmann, Finnish Meteorological Institute, tel. +358 50 3570323, stephanie.bohlmann@fmi.fi
Mika Komppula, Finnish Meteorological Institute, tel. +358 50 520 7500, mika.komppula@fmi.fi
Bohlmann, S., Shang, X., Vakkari, V., Giannakaki, E., Leskinen, A., Lehtinen, K. E. J., Pätsi, S., and Komppula, M.: Lidar depolarization ratio of atmospheric pollen at multiple wavelengths, Atmos. Chem. Phys., 21, 7083–7097, 2021.