Birch pollen in the air can be detected using lidar technology
Lidar measurements show that birch and spruce pollen cause a characteristic signature in the lidar signal. Lidar-derived particle depolarization ratio can be used to track pollen grains in the atmosphere.
Pollen detection is traditionally performed on roof level with so-called Hirst-type volumetric air samplers, but little is known about the vertical distribution of pollen in the atmosphere. In recent study, vertical resolved measurements were performed with the multi-wavelength Raman polarization lidar PollyXT.
An intense 11-day pollination event was detected from 5 to 15 May 2016. The event was separated into two parts due to different atmospheric conditions and the different mixture of detected pollen types.
The particle depolarization ratio, a lidar derived optical parameter which describes the rotation of the backscattered light and depends on the particle shape was used to detect the non-spherical pollen particles. During the first period which was dominated by birch pollen, an increased particle depolarization ratio was observed. During the second period a significant contribution of spruce pollen was observed in addition to birch. Spruce pollen grains are highly non-spherical, leading to an even larger depolarization ratio for the birch–spruce pollen mixture.
The results show that pollen can be detected using lidar measurements. Highly non-spherical pollen cause high depolarization values which can be used to detect the presence of the certain pollen type.
Results help to improve pollen forecast models
The finding of the study illustrates the potential of the lidar derived particle depolarization ratio to track pollen grains in the atmosphere. It will be used to improve particle classification using lidar measurements. Furthermore, the evaluation of pollen transport models with lidar measurements can potentially improve the performance of pollen forecast models.
Birch pollen is one of the most allergenic pollen types and the most allergenic tree pollen in northern, central and eastern Europe. It can irritate the respiratory system and cause asthmatic symptoms. In addition to this well-known allergenic impact, pollen also affect the climate as they can, for example, affect the formation of clouds.
Measurements were done at Vehmasmäki measurement site, in Kuopio, Finland. In addition to lidar measurements, multiple in-situ instruments were operated including a Hirst-type pollen sampler.
Further information:
MSc Stephanie Bohlmann, Finnish Meteorological Institute, tel. +358 50 3570323, stephanie.bohlmann@fmi.fi
Bohlmann, S., Shang, X., Giannakaki, E., Filioglou, M., Saarto, A., Romakkaniemi, S., and Komppula, M.: Detection and characterization of birch pollen in the atmosphere using a multiwavelength Raman polarization lidar and Hirst-type pollen sampler in Finland, Atmos. Chem. Phys., 19, 14559– 14569, https://doi.org/10.5194/acp-19-14559-2019, 2019.