The requirement to meet the Low Emission Zone (LEZ) engine emission standards as set out by the GLA in the Supplementary Planning Guidance: The Control of Dust and Emissions from Construction and Demolition can be met using the following techniques:
- Reorganisation of NRMM fleet
- Replacing equipment (with new or second hand equipment which meets the policy)
- Retrofit abatement technologies
- Re-engining
Retrofit fit is the process of fitting a new part that the NRMM equipment did not have when it was manufactured and is designed to make the NRMM meet a higher engine emission standard.
If the NRMM proposed for use within the LEZ does not meet the required emission standard then retrofit abatement technology to mitigate for both NOx and PM10 should be considered (or if it is not possible to retrofit for both pollutants then just PM10).
The most common method of retrofitting involves the installation of a diesel particulate filter (DPF) or catalytic convertor to the exhaust system of the NRMM. All diesel engines are potentially suitable for retrofit to mitigate particulate emissions but space within the engine compartment and cost may both be limiting factors.
There are several main exhaust treatment technologies used in retrofit and selection will normally be based on scale of reduction required and available budget.
| Technology
| Particulate emission reduction potential | NOx | |
Mass | Number | ||
| Wall-Flow Filter | >95% | >99% | <5% |
| Partial Flow Filter | 30-60% | No data | <5% |
| Diesel Oxidation Catalyst | <25% | No Impact | <5%
|
| Selective Catalytic Reduction | <10% | >70% | |
| Combined DPF+SCR | >95% | >99% | >70% |
Typical PM and NOx reduction potential for various retrofit devices.
Current engine emission standards are set using particle weight (Mass) but as medical research advances we are realising that the smallest (and therefore lightest) particles are the most damaging to health and it is likely that future engine emission standards will use particle numbers to specify limits.
As the above table demonstrates Wall-Flow Filters are the most effective of the available abatement technologies and almost completely remove particulate matter from the exhaust. Partial flow filters are often cheaper but significantly less effective and fail to remove many of the smaller particles that cause the most damage to human health. The diesel oxidation catalysts are primarily used to remove emissions of carbon monoxide and hydrocarbons in the exhaust. Alone they are unlikely to allow the NRMM to meet a higher emission standard but they are often used in combination with other filters to achieve the target emission reduction.