January 31, 2006
The Ministry of the Environment (MOE) announced the status of issuance of photochemical oxidant warnings*1 and reporting of damages in 2005. Photochemical oxidant warnings were issued in 21 prefectures, with a total of 185 days*2 (a total number of days on which the warnings were issued by a prefecture) (Fig.) in 2005. This number includes one day in which a photochemical oxidant alarm*3 was issued in Saitama prefecture on September 2, 2005.
Since the concentration of photochemical oxidants is affected by weather conditions, the number of days on which photochemical oxidant warnings are issued fluctuates yearly. The annual average of the maximum hourly value of photochemical oxidants during daytime has gradually increased, and in 2005 the maximum concentration of 0.258ppm was recorded at Ichihara area in Chiba prefecture on August 5, 2005.
Major causal substances of photochemical oxidants are nitrogen oxides (NOx) and volatile organic compounds (VOC). In line with the Air Pollution Control Law and the Automobile NOx/PM Act, the MOE has and will promote measures to reduce NOx at source. In May 2004, the Air Pollution Control Law was revised, with the aim of reducing VOC emissions. Under the revised law, VOC emitters are mandated to submit the specifications of VOC emitting facilities and to comply with the emission standards.
Also, the MOE has been operating the Atmospheric Environmental Regional Observation System (Soramame-kun) which monitors the state of air pollution in a wide area, collects real-time data and makes these data available on the Internet. Information concerning the issuance of photochemical oxidant warnings or alarms is available in this system. The information has also been available to mobile phone users since June 2002.
| Notes: | 1. | Paragraph 1, Article 23 of the Air Pollution Control Law stipulates that when the one hour value of the concentration of photochemical oxidants exceeds 0.12ppm and the state is expected to continue due to weather conditions, the warning should be issued to prevent damages to human health or the living environment. |
| 2. | The total number of days is the number of days on which the warnings are issued in a prefecture. Thus, even when two or more warnings are issued on a same day in different areas of a prefecture, it is counted as "one" day. | |
| 3. | Prefectures stipulate in their guidelines that when the hourly value of the concentration of photochemical oxidants exceeds 0.24ppm and the state is expected to continue due to weather conditions, the "photochemical oxidant alarm" shall be issued. |
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