Pollution on Chiswick High Road: what does the data say?

Guest blog by Professor Tom Pike

While London is by no means the most polluted city in the world, we still suffer from the health consequences of the air we all breathe. The London Air Quality Network (LAQN) of Imperial College estimates that up to 4,000 early deaths in 2019 can be attributed to our city’s pollution. For comparison COVID-19 has so far led to 15,000 extra deaths in London: in the past four years it is very possible more people have died early from pollution than from COVID-19, though it’s difficult to give pollution as a cause of death on an individual basis.  

Map of early deaths attributable to pollution for London in 2019. Source: Strategic Analysis, TfL City Planning (data from Imperial)

Imperial have produced a map of how all these 4,000 deaths are distributed over London. This map takes into account both the local levels of pollution and how susceptible the health of the population is to damage from air pollution – for example, how old they are.

For the four local government wards of Chiswick there were 24 early deaths from pollution in 2019 which compares to 55 deaths so far from COVID-19 over the past twelve months. It is clearly important to understand if efforts to try to reduce pollution are having an effect locally.

We know from a network of more than 200 monitoring stations across London that the prime source of pollution is road transport, as the NO2 concentration map from LAQN below makes clear. One of those stations by Chiswick High Road has been collecting measurements of three of the most damaging pollutants, NO2 and PM10 particulates since 2003 and the finer and even more damaging PM2.5 particulates since 2017. These pollutants have been clearly linked with causing damage to the heart and lungs.

Map of NO2 pollution for Chiswick and London from 2016 measurements. Source: LAQN

There has also been much research into estimating the economic costs of pollution associated with early death and damage to health. A recent study estimated these costs for 432 cities across Europe, finding that London paid the highest price, not because it had the worst air quality but as more people creating more wealth were harmed by pollution.

It’s possible to do the same calculations for Chiswick using the measurements for the individual pollutants monitored on the High Road and applying the costs per measured unit as estimated by the CE Delft study for the 22 cities in the UK. However, the measurements of pollution on the High Road don’t just reflect nearby traffic. London has a cloud of pollution hanging over it that depends on the weather and seasons as well as all the other sources of pollutants across London. For that reason, it’s necessary to compare the pollution measured on the High Road to that from our nearest background monitoring stations, at Barnes Wetlands Centre for NO2 and PM10, and North Kensington (at a spot away from a major road) for PM2.5.

Average cost of pollution as proportion of GDP for Chiswick High Road and the nearest background monitoring stations for every three-month period since monitoring was available in 2017 for nitrogen dioxide, NO2, PM10 and PM2.5 particulates . The most recent period is emphasised. Data: Air Quality England, LAQN; Calculation based on CE Delft

The plot above shows the costs of all three pollutants for the High Road and their total costs in terms of the local gross domestic product (GDP) compared to those from the background measurements. Each point represents a three-month average for each period since all three pollutants were monitored in 2017, with the most recent period emphasised. Overall, pollution costs Chiswick just over 3% of its GDP. As a comparison, nationally we spend 10% GDP on funding the NHS. The cost of pollution that can be clearly attributed to traffic on the High Road is the distance of each point above the corresponding background measurement, currently 0.5% of GDP for the area affected.

Cost of excess pollution for Chiswick High Road for each of the three-month periods. Source: Air Quality England, LAQN; Calculation based on CE Delft

To understand better how pollution has changed over time, the same data is shown above, but looking just at the difference between the High Road and background values. The amount of this excess pollution has fallen and rather more than can be explained by the drop in traffic counts on the High Road over this period (Department of Transport data available up to 2018). The fall off in diesel cars has played a part, possibly the withdrawal of the 27 bus service in 2019. COVID-19 restrictions lead to a drop in traffic levels generally across London durng the past year, but there has been a steady decline over the whole period of record keeping.

The latest three-month period also corresponds to the opening of C9, the temporary cycle lane along the High Road. Pollution has fallen further, more than twice the average drop seen since the start of the pandemic. In particular PM10’s have been eliminated as a source of excess pollution on the High Road and these levels now very closely follow the Wetlands Centre’s. Excess PM2.5 levels have also dropped to their lowest recorded. Overall, air pollution levels on Chiswick High Road are at their lowest ever value.

It’s possible to estimate these costs in pounds using values for the local GDP and population from the ONS and on the basis that the High Road contributes about 10% of the excess pollution, in line with its share of total traffic through Chiswick. In terms of health costs, if the drop in the last three months is compared to the previous period, that comes to a health-cost saving of £410,000 a year. If the comparison is to the average cost since the 27 bus service was withdrawn, it’s £920,000 a year.

As a cost comparison, the installation of C9 is estimated at £600,000, (based on the published £320,000 cost of the cycle lanes on Kensington High Street). Even if only a small fraction of the reduction in pollution can be attributed to C9, the saving in health costs represents a very high return on the investment in installing C9.

Though such estimates have a considerable inherent uncertainty, pollution continues to cost London dearly in both human and financial terms. However, the High Road is becoming a healthier place, with pollution falling further in the first three months since the new C9 cycleway opened.

Tom Pike is Professor in Electrical Engineering at Imperial College, London and lives in Chiswick 

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See also: TfL appoints operator to run temporary Hammersmith ferry service

See also: A year of pandemic – How has Chiswick fared?

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