Air pollution in Tokyo, which was plagued by industrial smoke and emissions from factories during the 60s and 70s, improved substantially in subsequent years. However, due to the ever-increasing growth of automobile traffic and diesel vehicle emissions, nitrogen oxides (NOx) and particulate matter (PM) continued to affect air quality in Tokyo. As a result, the Tokyo Metropolitan Government, in conjunction with the eight prefectures and municipalities, began in October 2003, a program to reduce NOx and PM emissions. Of vehicular emissions, diesel vehicles are responsible for about 80% of the NOx emissions and almost all of the PM emissions. The PM contained in diesel vehicle emissions is suspected to be carcinogenic, is an allergen and is linked with respiratory system disorders.

In accordance with their Ordinance on Environmental Preservation, the Tokyo Municipal Government began implementing diesel vehicle emissions control regulations in October 2003. The types of diesel vehicles subject to these regulations include buses, trucks, and special category vehicles like concrete mixers, garbage collection trucks, and refrigerator/freezer vehicles. When enforcement began, diesel vehicles more than seven years old, failing to meet the PM emissions regulation of the Ordinance were banned from traveling through the metropolitan area. Such vehicles are to be replaced with low-pollution vehicles or equipped with a diesel PM reduction system certified by TMG.

In June 2001, the Tokyo Municipal Government established guidelines for the designation of a certified PM reduction system. For the certified PM reduction system applicants, a board of examiners comprised by experts conducted the inspections and the designations. Through a local representative, Nett Technologies submitted their SF catalyzed diesel particulate filter for certification. In January of 2003, Nett’s SF filters were inspected and certified for use in Metropolitan Tokyo and the eight prefectures and municipalities.

Nett SF catalyzed diesel particulate filters utilize ceramic wall-flow monoliths to trap PM and offer unsurpassed filtration efficiency in excess of 95%. The surface of the filter is coated with a proprietary catalyst, which has the ability to lower the PM combustion temperature. In contact with the catalyst, the collected PM burns off at temperatures found in the exhaust gases during regular operation of the vehicle. Thus, a self-regeneration of the filter is facilitated. Nett filters operate virtually maintenance-free on most heavy-duty diesel engines which operate under frequent high-load conditions.