Martyn Willes' letter suggesting that clean air technology be considered for Hong Kong (South China Morning Post, August 27), is pie in the sky. For years Hong Kong authorities have sat on their hands when faced with air pollution problems. To suggest that alternative fuels be considered is like asking for the moon. The simplest way to clean up Hong Kong's air is to enforce a law that bans all vehicle drivers from keeping their engines running when stationary. Daily, one finds drivers all over the territory sitting in their parked vehicles, enjoying the air-conditioning, while their exhausts spew out gallons of poison. Bus drivers are among the worst offenders. I'm prepared to wager that air quality in the territory will be 50 per cent cleaner, if such a law is enforced. T.L. SANTOS Mid-Levels