CITYBUS is a ''green organisation'' - committed to minimising the potential adverse effects which public service vehicles can have on the environment. And in polluted Hong Kong this is no small commitment. Citybus was the first major bus company to introduce air-conditioned buses into Hong Kong on a large scale. These systems considerably reduce the levels of air-borne pollutants which passengers endure in non-air-conditioned buses in addition to providinga pleasant travelling environment. Citybus' fleet is mainly air-conditioned, with the exception of the private hire buses - which consist of a handful of open-top and vintage buses - and half the buses running on the number 26 route. The type of power unit utilised in the majority of Citybus meets or betters legislation for the four principal types of emissions from a diesel engine which may pose an environmental risk: gaseous emissions, particles, smoke and noise. Developmental work is ongoing with engine technology, and Citybus was the first bus operator in the world to have fitted a new generation Gardner engine to one of its vehicles. This ''futuristic'' engine has been designed to meet all legislation for the four principal types of emissions, and the vehicle has undergone fuel efficiency tests under Hong Kong's arduous operating conditions. As well, various ceramic coatings were tested to enhance the performance of the air-conditioning systems and this resulted in increased fuel economy and, consequently, the reduction of air-borne pollution from the engine. Ceramic coating also acts as a insulator and, when used in the engine compartment, can significantly reduce noise. The majority of air-conditioning systems, whether household, industrial, car or commercial, use chlorofluorocarbons (CFCs). The release of Freon-12 from a car's air-conditioning system contributes to the greenhouse effect, much more so than carbon gases emitted from vehicles. This effect that CFCs have on the environment has been recognised by Citybus and suitable equipment has been specified so that vehicle air-conditioning system refrigerants can be evacuated, recycled and re-used, thus minimising the release of CFCs intothe environment. Alternative refrigerants, which are more environmentally friendly, are being used on new vehicles. Fire extinguishers used on Citybus vehicles have also been investigated as these contain bromochlorodifluoromethanes (BCF) which can also have an adverse effect on the ozone layer. Alternative extinguishing methods are being investigated. Other areas which came under scrutiny included the specification of fuels and lubricants, non-asbestos brake-lining materials and, from a safety as well as an environmental point of view, the specification of materials which meet fire and toxicity regulations. Examples include fire retardants, low toxicity foam and moquette trim for bus seats, fire retardant treatment for wood-based materials (such as plywood) and floor covering materials. These materials exceed the stringent regulations applied to Civil Aviation aircraft. ''Citybus is doing everything within its power to contribute to the enhancement of the environment, and will continue to do so,'' said managing director Lyndon Rees.