Emissions Control Systems Manufacturers
The following links will lead you to emissions control systems manufacturers for retrofit applications:BASF Catalysts
Corning
Emitec
Ibiden
Johnson Matthey
NGK
Solvay
Umicore
Air Quality
To compare the current air quality in different European cities:Current Air Quality in Europe
Retrofit Worldwide
Other parts of the world also retrofit to reduce the pollution from existing vehicles
USA retrofit manufacturers
Arbeitskreis Partikel-Filter-Systemhersteller
VERT association
Schweizer Partikelfilter Verband
United Nations Environment Programme - Toolkit for clean Fleet Strategy Development
Diesel Engines and Diesel Emissions
Online information service on clean diesel engines and diesel emissionsDieselnet