Abstract
Concentrations of Nitrogen Oxide(NOX) and Non-Methane hydrocarbons(NMHC) that are the precursor substances of ozone are lower than the national average in the Fukushima prefecture. However the ozone concentration exceeded 120 ppb at Iwaki City (coastal region) in the Fukushima prefecture on 4 August, 2006. To investigate the causes of the high ozone concentration appearing in this coastal region, we analyzed the relation between the appearance of the high ozone concentration and meteorological elements. As a result, it was discovered that the high ozone concentration appeared over the coastal region in the following situations: 1) An anticyclone appeared over Japan and a subsidence inversion layer formed. Therefore, the vertical dispersion of ozone was reduced. 2) A heat low developed over the Chubu mountainous area , thereby a southwesterly wind prevailed over the Kanto region and the coastal region. Therefore, the long range transport of ozone from the Kanto region to the offing of Fukushima prefecture occurred due to the southwesterly wind. 3) A sea breeze circulation prevailed in the coastal region under weak pressure gradient conditions with the anticyclone, and the ozone transported from the Kanto region to the offing was transported from there to the coastal region by the sea breeze. 4) The high ozone concentration was lifted from the ground to the upper part of the mixing layer by convective mixing and the sea breeze circulation. Therefore, the ozone, of which the concentration was higher than that observed at the ground, existed in the region during the night. 5) During the day time, the concentration of ozone in the coastal region increased more than that of the previous day due to adding the ozone that was transported from the Kanto region and that which existed in the upper part of mixing layer.
