The presence of polyaromatic hydrocarbon in dust was analyzed at locations in two residential areas, a commercial area, an industrial area and a semi-industrial area, using a tape air-sampler from 1963 and a high-volume air sampler from 1967.
At the start of the study, benzo (a) pyrene maximum monthly average [1] levels were 70ng/m³ in the industrial area, 40ng/m³ in the commercial area, and 25ng/m³ in the residential area. Ten year later levels had fallen to below 10ng/m³ in all areas, and 25 years later to respective levels of 1.9, 1.6 and 2.6ng/m³. This change reflects the switch of energy source from coal to oil and the effectiveness of the Air Pollution Control Law.
This residential area value of 2.6ng/m³ is the same as that recorded at an automobile exhaust monitoring station. This suggests that even residential areas are greatly subject to the polluting influence of vehicle exhaust. Little difference between the three kinds of area is apparent in the annual mean values, which are 1.0, 0.8 and 1.0ng/m³ respectively.
Average annual concentration of benzo (a) pyrene at an automobile exhaust monitoring station was 1.4ng/m³ or 1.5 times higher than at other locations, suggesting a link between benzo (a) pyrene pollution and automobile exhaust.