Abstract
Observation of hourly atmospheric dust concentration by an automatic air sampler has been carried out from Feb. 1955 on the level of 53m above the ground at the Institute of Public Health.
The mean hourly variation of dust concentration for each month was similar to the result obtained by other investigators but slightly differs from them. In this survey, the concentration in the morning had two maxima from April to September.
The dust concentration in the midnight decreased exponentially with elapsed time, and the dissipation coefficient k increased linealy with wind velocity.
From our analysis, it may be concluded that on the day with unstable atmospheric condition the particulate matters in the atmosphere are dispersed by turbulence caused by solar heating rather than wind.
Under the meteorological conditions of rainy days, the concentration of smoke near the ground had a increasing tendency in the day-time, rather than decreasing one due to the washing effect of rain.
