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Climate Change

According to research commissioned by the Greater London Authority, the capital’s poor air quality contributed to the equivalent of 4,267 premature deaths in London in 2008.

Time for a clean up

It is to help curb this – and to meet European Union (EU) targets for air quality that were meant to have been hit in 2005 and have still not been achieved – that London mayor Boris Johnson published his air quality strategy on 14 December last year.

This sets out a framework for improving London’s air quality and outlines measures aimed at reducing emissions from a number of sectors, including transport. The initiatives proposed include an age limit for taxis and retrofitting older buses, as well as promoting electric cars and other low emission vehicles.

The strategy also proposes specific targeted measures being taken for areas where air quality is poor, and one example of this was the launch by Transport for London (TfL) last November of an innovative road surfacing trial to clean up the air in the capital’s most polluted areas.

Binding dust to the ground

It aims to demonstrate how to reduce the amount of particulate matter of less than 10µm in diameter, known as PM10, in the air by binding it to the road surface.

PM10 is produced mainly by engine emissions and tyre and brake wear and can exacerbate respiratory conditions in the elderly and very young. European legislation demands that levels do not exceed 50mg/m³ more than 35 times a year.

To tackle it, a dust suppressant solution called Calcium Magnesium Acetate (CMA) is sprayed onto the road, and this binds particulates to the carriageway and prevents it re-circulating.

It has been used at two sites in London – on the A3211, from Waterloo Bridge to Tower Hill, and on the A501 – Marylebone Road and Euston Road from Edgware Road to King’s Cross station.

“The research is pretty robust in a number of sites, and we also looked at the use of CMA in Warsaw, which saw a 10% reduction in particulate matter”

Will Fooks, TfL

The two sites chosen are areas where London is closest to exceeding the EU limits, says TfL’s head of strategy and business development for surface transport Keith Gardner. The project is being delivered in partnership with Ringway Jacobs, TfL’s highway maintenance and works contractor. 

TfL’s principal transport planner for surface transport Will Fooks says that TfL began to examine the potential of CMA after the publication of a report in 2009 which examined the effectiveness of different measures to reduce the PM10 levels along streets in Stockholm.

The report, by the Stockholm Environment and Health Administration, found that the application of CMA is efficient in reducing levels of PM10, with its use resulting in an average reduction of around 35%. Other methods examined, including intense sweeping of the streets and washing with high pressure water systems, only had marginal impact.

Six month trial

The dust suppressant solution being used in the London trial is applied to roads at night several times a week from a modified road gritting vehicle, after they have been swept and washed by a road sweeper. The particulates are then either washed away by rain or cleaned by road washing, preventing them entering the atmosphere.

The trial has a total budget of £300,000 and will last for six months. TfL hopes that PM10 levels will be reduced by 10-20% where it is used, and Fooks said that part of the trial will include spraying the PM10 in different concentrations to measure its effectiveness.

The length of the trial will also allow it to be tried in different seasons. Early indications, Fooks says, show that the harsh winter weather the capital faced in December “is reducing the CMA’s ability to work”. However, he adds: “It still worked to bind waste to the ground on top of the grit. The programme at the two sites depended on how much gritting they have to get through, and the CMA was then applied on top.”

Monitoring of the project is being undertaken using road side particulate monitors that form part of the London Air Quality Network, and an 800m stretch of road in Bloomsbury is being used as a control site in the trial.

Results will not be available until autumn 2011, but TfL has already begun to assess the potential of future uses, including deploying CMA to suppress particulates at construction sites where the levels can also exceed European limits.

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