Deposition of Aerosols on Leaves in a Cool-temperate Larch Forest in Northern Hokkaido, Japan

Abstract

Aerosol concentrations at the CC-Lag site in the Teshio Experimental Forest increased from winter to spring and sometimes showed extremely high values associated with Kosa and/or forest-fire events. The range and mean of the mass concentrations of aerosol chemical species were as follows: total particulate mass, 1.2-29, 5.0; elemental carbon, 0.061-2.2, 0.43; organic carbon, 0.059-3.5, 0.79; and sulfate, 0.12-6.2, 1.8 <TEX>${\mu}g/m^3$</TEX>. The total masses of the deposited particles on hybrid larch and on bamboo leaves were approximately 35 and 30 <TEX>${\mu}g/cm^2$</TEX>, respectively. The amounts of soil particles on the leaves were 6 <TEX>${\mu}g/cm^2$</TEX> for the upper part of hybrid larch, 2 <TEX>${\mu}g/cm^2$</TEX> for the lower part of hybrid larch, and 1 <TEX>${\mu}g/cm^2$</TEX> for Sasa bamboo leaves. The amounts of deposited black carbon were 2.3 <TEX>${\mu}g/cm^2$</TEX> for the upper part of hybrid larch, 0.6 <TEX>${\mu}g/cm^2$</TEX> for the lower part of hybrid larch, and 0.2 <TEX>${\mu}g/cm^2$</TEX> for Sasa bamboo leaves. Half of the total deposited particular mass was attached on the hybrid larch; however, most of the total deposited mass was adhered on the Sasa bamboo leaves. Regardless of the species, there tend to be more deposited particles on the leaves in the upper part than in the lower part, with only a few meters height difference. Comparing the composition of the deposited particles to that of the atmospheric aerosols without any size cut, the fractions of water-soluble material sulfate and sea salt in the deposited aerosols were about one tenth and one hundredth lower than that in the aerosols, respectively. On the basis of the measured concentration and the deposited amount on leaves, the deposition velocity of black carbon was estimated to be approximately 0.5 cm/s.