The Proposed T-charge Amendment to the London Congestion Zone: Where are the affected cars located?

The recently elected Mayor of London, Sadiq Khan, has tabled a proposed modification to the London Congestion Charge which will involve a supplementary charge levied against cars with older European emission bands (details can be found @ https://www.london.gov.uk/press-releases/mayoral/mayor-unveils-action-plan-to-battle-toxic-air). At the moment, the information provided by the Mayor of London's office indicates that cars which are not compliant to the Euro 4 emission standards will be required to pay an additional £10 per day to enter the charging zone. Some obvious questions to ask are how many cars will be affected by this modification and where the affected cars are located?

The figure inserted gives some preliminary statistics about London's private car fleet (data are for the end of 2015). Around 2.4 million private cars are registered in the Greater London Area, with the top ring chart showing that 41% of these vehicles are not compliant with the Euro 4 emissions standard. The bottom ring chart shows that 84% of these non-compliant cars have a petrol engine whilst 16% are fuelled by diesel. The histogram illustrates that the proportion of pre-Euro 4 car registrations varies substantially across the neighbourhoods of London (Lower Super Output Areas or LSOA).

The map inserted above shows the proportion of pre-Euro 4 cars registered per neighbourhood (LSOAs). We can see substantial differences across London. Some boroughs, such as Hackney (48.3% of the fleet) and Newham (46.7% of the fleet), have relatively high levels of per-Euro 4 car registrations. Others, like the boroughs of Westminster (35.8% of the fleet) as well as Kensington and Chelsea (33.9% of the fleet), have a relatively low level being pre-Euro 4. Illustrating the spatial variation that exists in the proportion of vehicles affected by this proposed modification represents one of the first steps in understanding the impact the amendment will have on the vehicle stock as well as households.

The Rated Nitrogen Oxide Emissions Factors of the United Kingdom’s Local Car Fleets

Recently, the discussion concerning the emissions from car operation has shifted away from being primarily focused on carbon dioxide, which is a prominent global pollutant contributing to climate change, towards the emission of local pollutants such as nitrogen oxides, particulate matter and black carbon. These local pollutants reduce air quality and can have significant impacts on public health, contributing towards respiratory and cardiovascular disease, and are become a prominent issue in local and national political debate.

 Interestingly, when you do a simple correlation analysis between the mean rated grams of carbon dioxide emitted per kilometre (gCO2/km) and the mean rated grams of nitrogen oxide emitted per kilometre (gNOx/km) of the car fleets registered across the local authorities of the UK, a insignificant relationship is estimated. This indicates that the global emissions factor (measured in mean gCO2/km) and the local emissions factor (measured in mean gNOx/km) of the local car fleets is not connected.

 The map below illustrates the mean gNOx/km of the car fleets registered across the local authorities of the UK in 2014. In this instance, it is evident that some of the areas which are experiencing air quality problems (such as the boroughs of London) have car fleets with relatively low NOx emission factors whereas some of the more rural locations of the UK (such as the South West of England and Wales) have fleets with comparatively high NOx emission factors. This finding has a number of important implications, notably that the gradual technical improvement of the car fleet in terms of NOx emissions is not necessarily transferring into improvements in the air quality in certain areas.