In Japan, almost the same degree of acid rain impact is observed as in Europe and America from which damage has already been reported. However, the impact on the ecosystem has not been clarified yet. Since in general, the damage by acid rain surfaces after a long period of time, if acid rain continues at the present rate, the damage of acid rain may become actualized.

## (2) Photochemical oxidants

Photochemical oxidants are generated as the secondary product of photochemical reactions when primary pollutants

mainly consisting of nitrogen dioxide and hydrocarbons that are emitted from factories, offices, and automobiles receive irradiation from sunlight. Photochemical oxidants cause photochemical smog that irritates the eyes and throats or influences the respiratory organs, however, the level of photochemical oxidants still exceeds the environmental standard in almost all the areas nationwide.

## (3) Nitrogen oxides

Nitrogen oxides that adversely affect the respiratory organs at high concentration are generated mainly by material combustion. They are mainly generated from stationary sources such as factories and mobile sources such as automobiles.

The annual average concentration of nitrogen dioxide in 2000 was slightly higher than that of the previous year, however, the long-term view shows that the concentration remains almost at the same level. For the environmental standard achievement statuses for nitrogen dioxide in 2000, the Ambient Air Pollution Monitoring Station indicated 99.2% and the Automobile Exhaust Gas Monitoring Station indicated 80%. However, the standard has not been satisfied over a wide area surrounding the urban areas that are specified by Automobile NOx Control Law (Law Concerning Special Measures for Total Emission Reduction of Nitrogen Oxides from Automobiles in Specified Areas) and the condition of air pollution is still unsatisfactory. Based on this reason, the implementation was enhanced by amending the Automobile NOx Law in 2001.

## (4) Suspended particulate matter

Suspended particulate matter is particles with diameter of 10 micro meters or less and float in the air. Suspended particulate matter consists of two categories: primary particles such as diesel exhaust particles that are emitted from diesel automobiles and fling-up soils; and secondary particles that are produced by changing gaseous substances such as nitrogen oxides into particles in the air. Being extremely small, such matters stay in the air for a long time, are deposited in lungs and the trachea, harming the respiratory organs at high

Transition of annual average concentration levels of nitrogen dioxide

Transition of environment standard achievement status associated with nitrogen dioxide in specific regions (Roadside air pollution monitoring station)

Notes: 1. Specific regions include some regions that are targeted for Automobile NOx Law in Saitama Prefecture, Chiba Prefecture, Tokyo, Kanagawa Prefecture, Osaka, and Hyogo Prefecture.

2. Air pollution by nitrogen dioxide based on the environmental standard is assessed as follows; among the daily average of nitrogen dioxide in each measurement station, the value is assessed from the lower value to that equivalent to 98%.

Presentation: Prepared by the Ministry of the Environment based on the "2000 Air Pollution Status Report"

## Transition of annual average concentration level of suspended particulate matter

Source: "2000 Air Pollution Status Report" by the Ministry of the Environment