Detection and characterization of birch pollen in the atmosphere using a multiwavelength Raman polarization lidar and Hirst-type pollen sampler in Finland
2019
Abstract. We present the results of birch pollen characterization
using lidar and in situ measurements based on a 11 d pollination period
from 5 to 15 May 2016 at the European Aerosol Research Lidar Network
(EARLINET) station in Vehmasmaki (Kuopio; 62 ∘ 44 ′ N,
27 ∘ 33 ′ E), Finland. The ground-based multiwavelength
Raman polarization lidar Polly XT performed continuous measurements at
this rural forest site and has been combined with a Hirst-type volumetric
air sampler, which measured the pollen type and concentration at roof level
(4 m). The period was separated into two parts due to different atmospheric
conditions and detected pollen types. During the first period, high
concentrations of birch pollen were measured with a maximum 2 h average
pollen concentration of 3700 grains m −3 . Other pollen types
represented less than 3 % of the total pollen count. In observed pollen
layers, the mean particle depolarization ratio at 532 nm was 10±6 % during the intense birch pollination period. Mean lidar ratios were
found to be 45±7 and 55±16 sr at 355 and 532 nm,
respectively. During the second period, birch pollen was still dominant, but
a significant contribution of spruce pollen was observed as well. Spruce
pollen grains are highly nonspherical, leading to a larger mean
depolarization ratio of 26±7 % for the birch–spruce pollen mixture.
Furthermore, higher lidar ratios were observed during this period with
mean values of 60±3 and 62±10 sr at 355 and 532 nm,
respectively. The presented study shows the potential of the particle
depolarization ratio to track pollen grains in the atmosphere.
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