Authorities will urge residents to stay indoors if the level of toxic smog spreading to Japan from China is expected to exceed twice the maximum limit set by the central government, officials said.
The Environment Ministry guidelines say prefectural governments will recommend that people, especially those with heart or lung diseases, the elderly and children, refrain from going outside or ventilating their homes if the average amount per day of the air pollutant PM2.5 (particulate matter 2.5 microns in diameter) is projected to top 70 micrograms per cubic meter.
The ministry has set a limit of less than 35 micrograms for the pollutant found in toxic smog. The alert will be issued if the level exceeds 85 micrograms in an hour in the early morning, since the average amount per day would then be expected to surpass 70 micrograms, based on past monitoring data analysis.
The alerts will be not legally binding, according to the ministry, which set the guidelines based on findings on health hazards caused by PM 2.5 and standards in the United States.
The hazardous particulate matter PM2.5 can be absorbed by the lungs and cause heart and lung disease.