Long-Range Transport of Air Pollution under Light Gradient Wind Conditions

Abstract

The long-range transport of air pollution on clew days under light gradient wind conditions is investigated from an analysis of all days with high oxidant concentrations in 1979 at locations in central Japan that are far from pollutant sources. Surface-level wind and pressure distributions over a 300×300 km area were analyzed, together with concentration isopleths of oxidants and suspended particles produced by photochemical reactions. It was found that the transport mechanism consists of. 1) land/sea breezes; 2) a steady onshore wind driven by the diurnal-mean land–sea temperature difference; 3) the generation of a strong thermal low in the inland mountainous region in the daytime; and 4) a subsidence inversion accompanied by a synoptic-scale high pressure system. The last three mechanisms work to combine land/sea breezes and slope and valley winds into one large-scale high-speed wind field that transports pollutants a long distance inland into the mountainous region.