STEFFI Graf and Michael Stich have two things in common, they are German tennis champions and are sponsored by Opel, the leading producer of environmentally friendly cars. Euromotors, the distributor of Opel cars in Hong Kong, will display four of the range at the Green World Expo. Peter Chan, general manager for Euromotors, said: ''Tall buildings, narrow streets, minibuses and air-conditioners all play a part in Hong Kong's air pollution problem. For this reason, environmentally friendly cars are so important.'' The four models on display will be the Corsa, the Astra, the Vectra and the Calibra. While the motor vehicle may have an environmental image problem, Opel is proving just how many features can be made harmless. One advance has been the ECOTEC engine, which is noted for low emission levels and small fuel consumption to maximum power ratio. All models have three-way catalytic converters, which reduce carbon monoxide emissions. Water-based paint technology has been perfected, so emissions from paint solvents in car manufacturing plants have been reduced dramatically. The German Car Industry Association has adopted the practice of identifying codes on all car plastic parts to aid recycling, a method started by Opel. More than 98 per cent of the Opel Astra can be recycled. The Astra features an unusual clean air filter, which removes up to 60 per cent of dust and pollen spores. Other Opel research and development projects include the use of lower emission fuel known as bio-diesel and the production of electric cars. Not only are environmental concerns the subject of Opel research, enhanced safety designs are also emphasised. Anti-collision bars, tensionable seat belts, anti-lock braking systems and airbags feature in different models. Mr Chan said: ''The Japanese domination of the local car market has ended. European cars have increased in popularity over the past five years. ''This is because Hong Kong car buyers associate European cars with better engineering and performance, safety and prestige.'' Opel's quest for excellence had led to a market share of 12.5 per cent of the European market, Mr Chan said. The Opel Corsa, the smallest in the range, was proving popular, he said.