[A-AS11] 大気化学

[AAS11-04] 森林火災から大量に放出される微小灰エアロゾル粒子の発見

*足立 光司¹ (1.気象研究所)

キーワード：エアロゾル、森林火災、透過型電子顕微鏡分析

This presentation will show a recent finding of small ash particles (~ several micrometers or smaller) in biomass burning (BB) smoke samples collected from three aircraft campaigns (Fig. 1; Adachi et al., 2022). BB events are occurring globally with increasing frequency, and their emissions are having more impacts on human health and climate. Large ash particles are recognized as a BB product with major influences on soil and water environments (Fig. 1, bottom ash). However, fine-ash particles, which have diameters smaller than several microns and characteristic morphologies and compositions (mainly Ca and Mg carbonates; Fig. 1, Ash-bearing particles in left three TEM images), have not yet been explicitly considered as a major BB aerosol component either in field observations or climate models. This study measured BB aerosol samples using transmission electron microscopy (TEM) and ion chromatography during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign. This study shows that significant amounts of fine ash-bearing particles are transported >100 km from their fire sources (e.g., pie chart in Fig.1). Environmental chamber experiments suggest that they can act as cloud condensation and ice nuclei. This study also found considerable amounts of fine ash-bearing particles in the TEM samples collected during previous campaigns; the Biomass Burning Observation Project (BBOP) and the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaigns. These ash particles are commonly mixed with organic matter and make up ~8 % and 5 % of BB smoke by number and mass, respectively, in samples collected during the FIREX-AQ campaign. The measured ash-mass concentrations are approximately five times and six times greater than those of BB black carbon and potassium, respectively, scaling to an estimated global emission of 11.6 Tg year^-1 with a range of 8.8 to 16.3 Tg year^-1. Better characterization and constraints on these fine ash-bearing particles will improve BB aerosol measurements and strengthen assessments of BB impacts on human health and climate.

Caption for Figure 1
Schematic of the emission of ash-bearing particles and their number fractions. This figure is Fig. 1 in Adachi et al (2022). See the original caption for details.

Reference
Adachi, K, J.E. Dibb, E. Scheuer, J.M. Katich, J.P. Schwarz, A.E. Perring, B. Mediavilla, H. Guo, P. Campuzano-Jost, J.L. Jimenez, J. Crawford, A. J. Soja, N. Oshima, M. Kajino, T. Kinase, L. Kleinman, A.J. Sedlacek, R.J. Yokelson, P.R. Buseck, (2022). Fine ash-bearing particles as a major aerosol component in biomass burning smoke. Journal of Geophysical Research: Atmospheres, 127, e2021JD035657. https://doi.org/10.1029/2021JD035657