The decision by KMB to retire its oldest and most polluting buses is welcome. The 288 buses, which meet or fall below the Euro 1 emissions standard - the lowest of the European benchmark models - will all disappear by the end of the year. Unfortunately, more than 440 old buses owned by Citybus and First Bus will still be running on our streets until 2012. If KMB can do it, so can others. The two other bus companies should bring their deadline forward. The city's pollution levels are reaching dangerous levels. Our leading authority on air quality, Professor Anthony Hedley, is leaving the city because of the bad air. He is, in effect, giving up. Authorities recently trumpeted that air quality in the Pearl River Delta is improving. However, most of us do not breathe delta air - which is measured high above our heads - we breathe roadside air, and its quality is getting worse. The worst roadside polluters are buses. Because of inefficient planning and preferential franchise policies, many routes have more buses than needed. Operators and government planners must work to rationalise available buses running on those routes. More importantly, they need to introduce new buses that meet higher emission standards, such as those for Euro IV and V. About half of the KMB fleet is already of the higher standard European models, making it the cleanest of the three operators. But all three still field hundreds of buses that are of the lower Euro II and III models. While these are an improvement on the oldest, they do not meet the high standards that have been adopted across Europe. At the moment, there is no timetable for their replacement. While ultimately the city deserves non-polluting buses, the government's proposal to retrofit buses to reduce nitrogen oxide emissions - which aggravate asthmatic conditions and reduce the ozone layer in the atmosphere - should be taken seriously as an interim measure. Instead of making excuses, all three operators should co-operate whenever possible. In the meantime, they should give us a deadline to introduce truly environment-friendly buses.