Travel in London Travel in London

9. London’s air quality and greenhouse gas emissions and transport and public health
These averages do not however reflect the variability between individual site
characteristics and trends. In addition they reflect all pollution sources experienced
at a monitoring site and not just locally emitted pollution or road based pollution
specifically.
Pollutant concentrations in London are affected by emissions in London, pollution
from outside London and the UK, and other factors such as weather. Using
sophisticated statistical models it is possible to ‘remove’ the weather effect from
trends in concentrations of the main pollutants monitored at sites in the LAQN.
This allows for the production of trends where the impact of variable weather
conditions is reduced. An analysis recently conducted by Kings College has
quantified the following trends between 2008 and 2013:
• Nitrogen Oxide (NO x ) at roadside sites show a downward trend of 1.25 per cent
per year, equivalent to a total reduction over the six-year period of 7.5 per cent.
• NO 2 at roadside sites show a downward trend of 2.1 per cent per year,
equivalent to a total reduction over the six-year period of 12.6 per cent.
• PM 10 at roadside sites show a downward trend of 1.4 per cent per year,
equivalent to a total reduction over the six-year period of 8.4 per cent.
• PM 10 at background sites shows a downward trend of 0.65 per cent per year,
equivalent to a total reduction over the six-year period of 3.9 per cent.
• PM 2.5 at roadside and background sites shows a downward trend of 2.2 per cent
per year, equivalent to a total reduction over the six-year period of 13.2 per
cent.
Variability at individual air quality monitoring sites
Related to this, Kings College London also investigated the variability in changes in
roadside measurements across the Capital. Specifically this analysis looked at the
difference or ‘increment’ between the roadside measurement and that at an
equivalent background site to quantify the air pollution from traffic as distinct from
other regional and urban sources.
It is clear from this analysis that the traffic contribution to pollution concentrations
at some sites is improving much faster than at others. For example, NO 2 and PM 10
concentrations have reduced at Marylebone Road and other sites over the last four
years but this trend has not been seen at all roadside sites in inner London.
Marylebone Road is not unique in displaying these air quality improvements.
Understanding the reasons for changes at some sites and not others will provide
evidence on the types of policies and actions that can help reduce pollution across
London as a whole.
9.4 Greenhouse gas emissions
Unlike local air quality pollutants, which have direct impacts on the health of the
public, emissions of greenhouse gases such as carbon dioxide (CO 2 ) are of concern
because of their longer-term impact on global climate and the natural environment.
CO 2 reduction target
The Mayor’s Climate Change Mitigation and Energy Strategy (CCMES) set an overall
target to reduce CO 2 emissions in London by 60 per cent, against 1990 levels, by
2025. Transport would be expected to play it’s part in achieving this overall
reduction; however it accounts for slightly more than one fifth of CO 2 emissions
167 Travel in London, Report 8