降下ばいじん量と降水量の間の関係について(第2報)

Abstract

This report deals with the data obtained from the dust-fall monitoring net-work using deposit-gauges during the period April 1983-March 1984; those for the period April 1982-March 1983 have been published in the foregoing report. For the second period, another area was also studied in addition to the one for the first period; the former is situated along Mikawa bay, while the latter is located inland by some 60km northwards. This selection of areas might be regarded so suggestive that the data obtainable from them could be expected to provide useful information. The findings are as follows : For dust (M, t/(km)^2・mo) and rain (V, L/mo) both gathered by the deposit-gauge at a site, (1) a formula M/V=k・L/V+Δ is approximately applicable, the slope k being much the same as the annual average of dust-fall at the site. (2) More exactly, a nearly linear relation M=m+αV-βV^2 holds, where m is a constant independent of rain-fall and α as well as β constants affecting the collection efficiency of a rain-drop for a dust-particle. (3) The collection efficiencies calculated under such meteorological conditions as rain-fall intensity 0.1-1.0mm/h and rain-drop diameter 0.5-1.0mm are all of the order of magnitude (10)^<-2> or the like, those for the inland area remaining practically constant throughout the two periods and, as compared to these, those for the coastal area being about two times larger. (4) Further, the amounts of dust to be scavenged by rain are estimated at 2.8 and 2.3t/(km)^2・mo for the inland and coastal areas respectively. Additionally, mention was made of two reports measuring collection efficiency, one of them being concerned with a laboratory experiment using snow crystals for a polystyrene aerosol and the other being related to a field survey monitoring the amount of dust in air after rain-fall; their results are found to be in good agreement with those obtained by us.