Transport for LondonBus filters
Buses are now fitted with filters to reduce pollutants
The cost of fitting the entire fleet of 8000 buses has resulted in an investment of around £30million.
A typical London double decker bus emits 17.44kg of particulates a year but when fitted with a trap this is reduced to just 1.76kg.
The diesel particulate filter programme has seen the emissions of some of the most harmful air pollutants emitted by buses - such as fine particles, carbon monoxide and hydrocarbons - reduced by 90 per cent.
Since the programme started in 1999, huge amounts of pollutants have been prevented entering the air in London:
- Approximately 375 tonnes of fine particles - that's the weight equivalent of 28 double-decker buses
- 2,710 tonnes of carbon monoxide - that's enough carbon monoxide to fill 25 Royal Albert Halls
- 845 tonnes of hydrocarbons - that's the weight equivalent of 63 double-decker buses
How does the filter work?
The filters have been fitted within the exhaust stream of the buses. As the dirty exhaust gases pass into the first chamber of the particulate filter, two harmful pollutants - carbon monoxide and hydrocarbons - are virtually removed as they are converted by a catalyst into harmless gases.
The exhaust gases then continue through into a second chamber where a filter traps the fine particles and removes them from the exhaust stream.
How do we know these systems work?
The Millbrook London Transport Bus Test Cycle was developed by TfL to assess what the environmental benefits of these filters (and other technologies) would be under typical London operating conditions.
We tested a number of different buses fitted with these filters and the results repeatedly showed that emissions of fine particles, carbon monoxide and hydrocarbons were reduced by 90 per cent.
Once fitted, operators can apply for a Reduced Pollution Certificate, which reduces the amount of road tax to be paid on vehicles.
In order to have the certificate renewed each year, the filters are checked to ensure they are operating correctly. This is done as part of the vehicle's annual MoT.
In addition, London Buses also conducts engineering quality checks on buses used on the London network. These checks also include an inspection of the filter so that if any are found to be faulty, the operator will be notified and instructed to repair the system.
