Preprints
https://doi.org/10.5194/acp-2020-1281
https://doi.org/10.5194/acp-2020-1281

  18 Dec 2020

18 Dec 2020

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Lidar Depolarization Ratio of Atmospheric Pollen at Multiple Wavelengths

Stephanie Bohlmann1,2, Xiaoxia Shang1, Ville Vakkari3,4, Elina Giannakaki1,5, Ari Leskinen1,2, Kari Lehtinen1,2, Sanna Pätsi6, and Mika Komppula1 Stephanie Bohlmann et al.
  • 1Finnish Meteorological Institute, Kuopio, 70211, Finland
  • 2Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 3Finnish Meteorological Institute, Helsinki, 00560, Finland
  • 4Atmospheric Chemistry Research Group, Chemical Resource Beneficiation, North-West University, Potchefstroom, South Africa
  • 5Department of Environmental Physics and Meteorology, University of Athens, Athens, 15784, Greece
  • 6Biodiversity Unit, University of Turku, 20014 University of Turku, Finland

Abstract. Lidar observations during the pollen season 2019 at the European Aerosol Research Lidar Network (EARLINET) station in Kuopio, Finland were analyzed in order to optically characterize atmospheric pollen. Previous studies showed the detectability of non-spherical pollen using depolarization ratio measurements. We present lidar depolarization ratio measurements at three wavelengths of atmospheric pollen in ambient conditions. In addition to the depolarization ratio detected with the multiwavelength Raman polarization lidar PollyXT at 355 and 532 nm, depolarization measurements of a co-located HALO Photonics Streamline Doppler lidar at 1565 nm were utilized. During a four days period of high birch (Betula) and spruce (Picea abies) pollen concentrations, unusually high depolarization ratios were observed within the boundary layer. Detected layers were investigated regarding the share of spruce pollen to the total pollen number concentration. Daily mean particle depolarization ratios of the pollen layers on the day with the highest spruce pollen share are 0.10 ± 0.02, 0.38 ± 0.23 and 0.29 ± 0.10 at 355, 532 and 1565 nm, respectively. Whereas on days with lower spruce pollen share, depolarization ratios are lower with less wavelength dependence. This spectral dependence of the depolarization ratios could be indicative of big, non-spherical spruce pollen. The depolarization ratio of pollen particles was investigated by applying a newly developed method and assuming a backscatter-related Ångström exponent of zero. Depolarization ratios of 0.44 and 0.16 at 532 and 355 nm for the birch and spruce pollen mixture were determined.

Stephanie Bohlmann et al.

 
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Status: closed
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Stephanie Bohlmann et al.

Stephanie Bohlmann et al.

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Short summary
Measurements of the multi-wavelength Raman polarization lidar PollyXT and a HALO Photonics Streamline Doppler lidar have been combined with measurements of pollen type and concentration using a traditional pollen trap at the rural forest site in Vehmasmäki, Finland. Depolarization ratios were measured at three wavelengths. High depolarization ratios were detected during an event with high birch and spruce pollen concentrations and a wavelength dependence of the depolarization ratio was observed.
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