Since the introduction of tighter emissions standards for new vehicles and the vehicle LEZ implementations in London, air quality in the capital has improved. However, as emissions from vehicles have gone down, the proportion coming from construction machinery has increased and the mayor decided to tackle these emissions by introducing the London nrmm LEZ in 2015.

Up until 2020, machines working on major developments within greater London needed to meet EU Stage IIIA levels, while those working on those sites in the Central Activity Zone or Canary Wharf had to meet Stage IIIB limits. These limits only apply to machines between 37 and 560 kW although it is good practice to apply the limits to all sites and machines.

From 2020 these requirements tightened to Stage IIIB for Greater London and Stage IV for the Central Activity Zone and Canary Wharf and apply to all sites.

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The Mayor’s guidance on meeting these requirements is to either reorganise the fleet to use a machine that meets the required standard, obtain new equipment that meets the standards, fit a different engine that meets the standards to an existing machine, or retrofit an approved exhaust aftertreatment device registered on the EST scheme.

As Stage IIIB legislation is tighter for both NOx and PM, retrofit for both these pollutants should be considered but, if it is not possible to retrofit for both pollutants, then just particulate retrofit is acceptable. Generally, SCR is needed to significantly reduce NOx emissions and retrofit SCR is more difficult to implement for individual machines.

For constant speed engines (eg generators) there were no EU Stage IIIB or Stage IV limits set. From 2020, these constant speed engines need to meet EU Stage V emissions standards in the CAZ/CW. This effectively means the use of both a particulate filter and an SCR system.

Johnson Matthey DPF CRT® with SCR – The SCRT®


The Johnson Matthey range of DPFs are approved for London nrmm LEZ and HS2 and are registered on the EST scheme.

HS2 generally follows the London nrmm LEZ requirements but is one EU emissions stage stricter. A Johnson Matthey DPF can be used to take a Stage IV machine to Stage V equivalent to meet HS2 requirements in the Central Activity Zone.

Download London NRMM LEZ Page Other cities in the UK are looking at the London nrmm LEZ scheme and are considering whether to implement similar requirements.