The London Low Emission Zone Accountability Study

BEN BARRATT(1), Gary Fullyer (1), Frank Kelly (1)

(1) King's College London, London, UK

     Abstract Number: 74
     Last modified: October 19, 2009

Abstract
In February 2008, the first phase of the London Low Emission Zone (LEZ) was introduced, its primary aim being a reduction in PM10 across Greater London by targeting the most heavily polluting diesel vehicles. The zone covers an area of 2644 km$^2 in which more than 8 million people reside. A full accountability study has been ongoing since 2005, drawing together experts from a range of disciplines.

An LEZ monitoring network was established in 2006 following a baseline study supported by the HEI. A range of gaseous and particle metrics are being monitored in locations predicted by emissions modelling to experience the greatest impact from the LEZ. These monitoring sites are co-located with automatic number plate recognition (ANPR) cameras to provide a detailed vehicle fleet characterisation. In addition, short sampling campaigns are being carried out to establish the changing chemical composition of particulate matter.

ANPR data showed that while the introduction of the LEZ did not significantly change vehicle flows or composition, emissions classes of affected vehicles changed rapidly. Compliance rates of articulated HGVs entering the zone increased from around 80% in 2007 to more than 98% by the second half of 2008. The shift in 3.5t-12t HGVs was even greater (c. 75% to 97%). Initial analysis of the pollutant data suggests that this has led to a large decrease in concentrations of CBLK and non-regional PM2.5 at roadside locations (15% / 1 micro-gram/m$^3 per year in the two years prior to and one year following introduction of the scheme). This change was less well defined in central London where the diesel vehicle fleet has a far higher proportion of taxis and buses subject to independent emissions controls (HGV:Taxi ratio outer London 27:1, inner London 1:3). 60% of the total weekday inner London fleet were diesel in 2008, an annual increase of 4%. Source apportionment of PM10 revealed an underlying long-term downward trend in secondary and natural PM10 (c. 0.5 micro-gram/m$^3 p.a.), but an increase in primary PM10 (up to 0.6 micro-gram/m$^3 p.a.) contradictory to emissions inventory projections. No evidence of an LEZ-related impact on primary PM10 was found.

The initial phase of the London LEZ accountability study has identified a clear impact of the policy intervention on ambient pollution concentrations. More targeted associations between vehicle emissions, particle composition and toxicity are now being investigated. Following a change in political leadership, the next phase (inclusion of LGVs) has been delayed from 2010 to 2012, potentially delaying further improvements. The health response to the LEZ is being assessed through a cross sectional study of the respiratory health of school children in 15 schools, including biomarkers of exposure and DNA characterisation. An analysis of the distribution of consultations at primary care clinics is also planned. Each activity will be linked to provide an overall estimation of the London-wide health impact of the LEZ.

The study is ongoing and due for completion in 2012. Intermediate results will be published during 2010.