Detection and characterization of birch pollen in the atmosphere using a multiwavelength Raman polarization lidar and Hirst-type pollen sampler in Finland

摘要

We present the results of birch pollen characterization using lidar and in?situ measurements based on a 11d pollination period from 5 to 15?May?2016 at the European Aerosol Research Lidar Network (EARLINET) station in Vehmasm?ki (Kuopio; 62°44′N, 27°33′E), Finland. The ground-based multiwavelength Raman polarization lidar PollyXT 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 (4m). 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 2h average pollen concentration of 3700grainsm?3. Other pollen types represented less than 3% of the total pollen count. In observed pollen layers, the mean particle depolarization ratio at 532nm was 10±6% during the intense birch pollination period. Mean lidar ratios were found to be 45±7 and 55±16sr at 355 and 532nm, 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±10sr at 355 and 532nm, respectively. The presented study shows the potential of the particle depolarization ratio to track pollen grains in the atmosphere.