In 1938, the imperial navy built another oil refinery in Yokkaichi that would later become a target for American air raid bombing during the Pacific War.
[4] In 1955, the Ministry of International Trade and Industry began its policy to transition Japan's primary fossil fuel source from coal to petroleum, and oil refineries were once again opened in Yokkaichi.
[5] To accomplish the goal of the government-issued Petrochem Industry Program - Phase I from 1955, the Daichi Petrochemical Complex, a joint project of Showa Oil and Shell Oil Company, began construction in 1956 around the remnants of World War II naval fuel factories in south Yokkaichi Harbor which were destroyed by bombing before their operation began.
[4] In 1960, the government of Prime Minister Hayato Ikeda accelerated the growth of petrochemical production as part of its goal to double individual incomes of Japanese citizens over a 10-year period.
The Petrochemical Industry Program - Phase II began as the Ministry of International Trade and Innovation (MITI) announced that a second complex was to be constructed on reclaimed land in northern Yokkaichi.
[3] Researchers in the Journal of Environmental Health found in 1985 that as air quality decreased, mortality rate for bronchial asthma and chronic bronchitis cases increased.
[11] A study in 1975 from Mie University in Japan found a significant correlation between the number of Yokkaichi asthma patients and decrease in expected grain yield for May to September summer crops.
The high concentration of Yokkaichi asthma patients in Isozu Village can be further accounted for under this conclusion, as the source of sulfur trioxide emissions is 2 kilometers south of the most affected population.
[8] A 2001 study by several researchers in the Environmental Management journal confirmed by analyzing the effects of SO2 and SO3 on humans that SO3 was likely the real cause of the asthma.
The committee found that the Isozu district had six times the SO2 content in air of the rest of Yokkaichi and concluded that the asthma would likely cause an increase in mortality rate.
[4] When the pollution did not stop, angry fishermen from Isozu upset with the government's lack of action attempted to plug an industrial drainpipe belonging to Mie electric company with sandbags.
[4] The national government sent out investigators with the issue of the Special Survey Council on Yokkaichi Area Air Pollution in 1963, and they concluded their report in March 1964.
[14][15] Sulfur oxides have also been attributed to causing other Japanese city asthma outbreaks, such as in the Nishiyodogawa industrial district of Osaka, Japan.