The efficacy of low emission zones in central London as a means of reducing nitrogen dioxide concentrations

This paper considers the effects of different strategies that might be cons idered to reduce the impact made by road traffic on air pollution in London . The management of road traffic in large urban areas is one of many option s being considered to reduce pollutant emissions to meet statutory air poll ution objectives. Increasingly, the concept of a low emission zone (LEZ) is being proposed as a means of achieving this reduction. An assessment has b een made of different LEZ scenarios in central London, which involve reduci ng traffic flow or modifying the vehicle technology mix. Methods of predict ing annual mean nitrogen dioxide concentrations utilising comprehensive tra ffic data and air pollution measurements have been used to develop empirica l prediction models. Comparisons with statutory air pollution objectives sh ow that significant action will be required to appreciably decrease concent rations of nitrogen dioxide close to roads. The non-linear atmospheric chem istry leading to the formation of nitrogen dioxide, results in a complex re lationship between vehicle emissions and ambient concentrations of the poll utant. We show that even ambitious LEZ scenarios in central London produce concentrations of nitrogen oxides that are achieved through a "do nothing" scenario only five years later. (C) 2001 Elsevier Science Ltd. All rights r eserved.