Cleaning The Air

On Thursday afternoon the Environment Committee took evidence on the mayor's draft Air Quality Strategy. The main witness was Environment Adviser Isabel Dedring who is well liked and respected across the political spectrum at City Hall. Inevitably the discussion focused on the Low Emission Zone and plans to clean up diesel vehicles in the capital.

Where?

Although the Low Emission Zone covers the whole of the Greater London Area - give or take some unusual boundary quirks - the main problem is in the centre of town. There are pollution hotspots at major road junctions - Tower Hill, Marble Arch, Euston Road, Trafalgar Square and all along the Victoria Embankment. Heathrow Airport clearly shows up on the pollution map, but strangely there is no corresponding hotspot at London City Airport, although an increase in the number of jets may create one in future.

Against this evidence, I expressed surprise that successive additions to the LEZ restrictions would apply in outer London. Harefield, Enfield, Bromley and Havering all register the lowest levels of air pollution, yet owners of agricultural vehicles, motorised horse boxes and mini buses will all have to make expensive alterations to their vehicles, or even replace them, although those vehicles never go near the polluted areas. This seems unfair and - not surprisingly - I'm getting complaints from residents.

Particulates

Also known as PM10 emissions, these form a fine micro dust in the air we breathe and can irritate the lungs, particularly affecting asthma sufferers. The top three sources of PM10s in London are:

Black Taxi exhausts

Light goods vehicle exhausts

Tyre and brake wear from private cars

The move from petrol to diesel - encouraged by fuel prices and tax incentives - has led to more particulates whilst reducing carbon dioxide emissions. As particulates are more harmful than CO2 the tax regime looks perverse in large cities like London.

The strategy targets goods vehicles and black cabs but Isabel admitted that the particulate traps fitted to cabs had been less effective than predicted in many cases. I remember this being a hotly contested issue a couple of years ago when I raised cabbies' concerns with Livingstone. The Public Carriage Office did some tests which proved the modifications worked, Livingstone accused me of stirring up trouble and the whole thing was forgotten. It seems that there was a problem after all...

Nitrogen Oxides

The main polluter is nitrogen dioxide, a brown gas which is poisonous and has greater global warming effects than carbon dioxide, but the definition also includes nitrous oxide which is unstable and converts to nitrogen dioxide over time by combining with naturally occurring oxygen.

The three biggest polluters in London are:

Domestic gas boilers

Heavy goods vehicle exhausts

Private car exhausts

The new particulate traps being introduced for buses and HGVs also aim to reduce nitrogen oxide emissions.

The domestic boilers are a different problem, requiring planning law changes and retrofits. Decentralised power generation - meaning small power plants closer to homes - also has the potential to increase nitrogen oxide pollution. It is acknowledged that biomass boilers, which are included in many environmentally friendly developments, are more polluting than gas. When it comes to saving the world and cleaning London's air there are no easy choices and some of the solutions are contradictory.