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Press Release

Status of Photochemical Oxidant Warnings and Reported Damages in 2004

March 10, 2005

Ministry of the Environment (MoE) has compiled a report on the status of photochemical oxidant warnings and reported damages caused by photochemical air pollution in 2004. MoE requests prefectural governments to submit a report on the warning and reported damages between April and October every year, when the occurrence of the photochemical air pollution is considered to be most frequent.

Photochemical oxidant warnings were issued in 22 prefectures during the period in 2004, with 189 running days (total days on which the warnings were issued by a prefecture)*1, and the number of reported people who were affected by photochemical oxidant was 393 (Fig.).

*1 "Running days" is the total number of days on which the warnings issued in a prefecture. Thus, even when two or more warnings are issued on the same day in different areas of a prefecture, it is counted as "one" day.

Since concentration of photochemical oxidant is affected by weather conditions, number of days on which photochemical oxidant warnings*2 issued fluctuates by year. Annual average of the maximum hourly value during daytime has been gradually increasing. In July 2004, the number of days with issuance of the warning was high and the maximum concentration of the photochemical oxidant marked 0.233ppm at Chiba area in Chiba prefecture on July 16, 2004.

*2 Paragraph 1, Article 23 of the Air Pollution Control Law stipulates that when one hour value of the concentration of photochemical oxidant is more than 0.12ppm and the status is considered to continue due to weather condition, the warning should be issued to prevent damages to human health or the living environment.

Major causal substances of photochemical oxidant are nitrogen oxides (NOx) and volatile organic compounds (VOC). In line with the Air Pollution Control Law and the Automobile NOx/PM Law, the MoE has been and will be promoting measures on the reduction of NOx at source. The Air Pollution Control Law was revised on May 26, 2004 aiming at reduction of VOC emissions. The revised law aims to reduce VOC emissions by 30% compared to the value marked in FY 2000 by FY 2010. The target should be achieved through "best policy mix" approach, in which regulation and voluntary efforts are properly combined.

Since FY 2000, MoE has been operating the Area-wide Atmospheric Environmental Monitoring System (Soramame-kun) which monitors the wide-area status of air pollution and collect real-time data, and to make these data available on the Internet. Information concerning the issuance of photochemical oxidant alarms or warnings is available in this system. Also, the information is provided to mobile phones since June 2002.


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