5:15 PM - 6:45 PM
[AAS09-P16] Feasibility study of direct measurement of bio-aerosol emission flux from forest
Keywords:bioaerosol, flux measurement, forest
Bioaerosols (BA) are primary particles released from the biosphere, such as bacteria, spores, and pollen. To evaluate the influence of BA on the atmosphere, such as ice nuclei ability at relative higher temperature, it is necessary to evaluate emission flux from sources such as forests amd ocean. However, there are only few studies in which BA emission fluxes were directly measured in forests.
Because Minami et al.(2020) indicated that transport efficiency from the forest floor to the atmosphere was very small, we tried to measure the BA flux at the top of forest canopy by adopting the gradient method and the relaxed eddy accumulation (REA) method. The BA flux observations were conducted at an observation site in Namie, Fukushima Prefecture, during August-November 2022 and 2023. A 10.8-meter-high tower was installed in the forest at the observation site, and temperature and BA concentration were measured in the altitude range between 5.6 and 12.5 m. A sonic anemometer measurement and REA sampling were conducted at 11 m just above the canopy. BA was sampled on a filter using a low volume air sampler, BA amount was determined by fluorescence measurement and microscopic observation of the filter samples.
Altitude gradients of air temperature and BA concentration in the forest canopy are varied with altitudes because of blocking sun light and emission/deposition of BA in the canopy. Measuring those gradients, we determmined the altitude range where BA concentration and temperature decrease with altitude, In this altitude rage, we can eveluate significant values of the eddy-diffusion coefficient K and REA coefficient b from regression analyses between temperature gradient or temperature difference in upward/downward wind air with sensible heat flux.
By accumulating more BA on the filter, we can mesure gradient of BA concentration with altitude and BA concentratin difference between upward/downward wind air.
From these results, we can evaluate the BA emission flux from foerest canopy to the atmosphere by adopting the gradient meathod significantly. For successful REA method, we need more precise BA concentration measurement.
Because Minami et al.(2020) indicated that transport efficiency from the forest floor to the atmosphere was very small, we tried to measure the BA flux at the top of forest canopy by adopting the gradient method and the relaxed eddy accumulation (REA) method. The BA flux observations were conducted at an observation site in Namie, Fukushima Prefecture, during August-November 2022 and 2023. A 10.8-meter-high tower was installed in the forest at the observation site, and temperature and BA concentration were measured in the altitude range between 5.6 and 12.5 m. A sonic anemometer measurement and REA sampling were conducted at 11 m just above the canopy. BA was sampled on a filter using a low volume air sampler, BA amount was determined by fluorescence measurement and microscopic observation of the filter samples.
Altitude gradients of air temperature and BA concentration in the forest canopy are varied with altitudes because of blocking sun light and emission/deposition of BA in the canopy. Measuring those gradients, we determmined the altitude range where BA concentration and temperature decrease with altitude, In this altitude rage, we can eveluate significant values of the eddy-diffusion coefficient K and REA coefficient b from regression analyses between temperature gradient or temperature difference in upward/downward wind air with sensible heat flux.
By accumulating more BA on the filter, we can mesure gradient of BA concentration with altitude and BA concentratin difference between upward/downward wind air.
From these results, we can evaluate the BA emission flux from foerest canopy to the atmosphere by adopting the gradient meathod significantly. For successful REA method, we need more precise BA concentration measurement.