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.
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