Abstract
In order to obtain knowledge for urban and regional planning suitable for the prevention of air pollution, meteorological conditions for high concentrations of air pollutants were statistically investigated, using hourly NO2, NOx, Oxidant (Ox), SO2 and SPM concentration data measured at 73 monitoring stations in Nohbi Plain, for the period from April 1985 to March 1987.
First, daily-averaged and daily-maximum concentrations of air pollutants were computed for each year. Secondly, by using these concentrations, “high concentration” days were selected in 6 areas for April 1985 -March 1986 and for April 1986-March 1987. The “high concentration” days stand for those concentrations which fall within the highest thirties, in over 70% of all monitoring stations, or stand for the days more than 2 areas over 50% of all stations fall within the highest thirties, for daily average of daily maximum concentrations. Thirdly, for those selected days, the diurnal variations of pollutants and meteorological factors, such as wind speed, wind direction and atmospheric stability, were analyzed. Fourthly, vertical structure of atmospheric temperature, wind direction and wind speed were compared among the two types of “high concentration” day (i. e. good weather with weak wind or bad weather with weak wind), using rawinsonde soundings in South Nagoya from 28 November to 7 December 1990.
Obtained results are as follows: in monthly variations, most high concentration days appeared during the cool period (i. e. from October to March) except for Ox Especially, NOx showed that tendency clearly. The main meteorological conditions for the high NO2 days were “bad weather with weak wind” and “good weather with weak wind”, while high Ox days appeared with “extended land and sea breezes”. Thus, a relationship was shown between high Ox and the sea breeze blowing from the southern industrial area along Ise Bay. However, high Ox days selected by daily average also occurred with “good weather with northwestern wind”. In the latter case, high Ox depended on ozone supply from the stratosphere by a travelling anticyclone.
Though the high SO2 and SPM concentrations days appeared mainly with “good weather with weak wind” or “bad weather with weak wind” in cool periods, sometimes they occurred with “land and sea breezes” in warm periods. These results showed that the high SO2 and SPM days in warm periods depended on advection of pollutants from coastal area.
