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Something in the air

Source: PSE - Aug/Sep 15

In light of the ruling by the Supreme Court on UK air quality plans, Steve Rawson, head of retrofit engineering at Eminox, looks at options available to local authorities.

When the Supreme Court justices made their ruling in May, the culmination of a five-year battle fought by ClientEarth, they were unanimous in their decision, saying: “The new government, whatever its political complexion, should be left in no doubt as to the need for immediate action to address this issue [of air pollution].” 

This ruling was against a background of the UK being in breach of European legal limits for nitrogen dioxide (NO2) and potentially faced with being fined by the EU for its failure to meet the regulations. Many believe that councils may be liable to pay ‘all or part’ of any such fines from the EU. Whilst it may be possible to exclude certain types of vehicles from pollution hotspots, this is not a viable option with essential vehicles such as buses. As a result, cost-effective solutions are needed to reduce emissions, particularly NO2, from existing vehicle fleets. 

It has been widely reported that particulate matter (PM) in the air causes about 29,000 deaths in the UK each year. However, the true figure could be much higher, as it excludes deaths from NO2 emitted by diesel vehicles. COMEAP, the Committee on the Medical Effects of Air Pollutants, is expected to publish figures – including deaths caused by NO2 – later this year. The gas affects lung function and lung development in children. 

Near-zero emissions 

In light of the Supreme Court ruling, we are reinforcing the message that there is a cost-effective and immediate way to cut NO2 and other pollutants by more than 95% without having to buy new vehicles. Achieving Euro 6 emissions levels, as well as specifically reducing NO2, is possible by combining two exhaust after-treatment systems – SCR (selective catalytic reduction) and CRT (continuously regenerating trap) in a retrofit SCRT system. 

These systems have been designed specifically for challenging urban duty-cycles – and the evidence of what it can achieve is clear. Independent tests on what is known as the MLTB cycle, which simulates urban bus operation, demonstrated NO2 reduction of 96.7%, along with NOx (95%), PM (98.8%), HC (98.1%) and CO (96.5%). Field data supports this, with consistent reductions in excess of 95%.

 Reducing roadside NO2 

Air quality experts at King’s College London have attributed a 16% reduction in NO2 pollution on Putney High Street to SCRT technology retrofitted to 93 buses. We upgraded the buses between April and July 2013 and King’s College identified a clear decrease in NOx and NO2 concentration during the same period. 

NO2 concentrations on Putney High Street were well above legal limits before the retrofitting with our SCRT. As well as the large drop in kerbside NOx, there was a sustained decrease in NO2 concentrations of 12% (kerb) and 16% (façade) over the full period of the study. This has been particularly effective in reducing the number of short-term exceedances of NO2 limits. 

Lower emissions than Euro 5 hybrid 

We recently supplied our SCRT system to Brighton for fitting on Euro 3 buses. The technology was tested against other buses on a route in the city centre that traverses Brighton & Hove through a known air pollution hotspot. 

The bus was fitted with a Portable Emissions Monitoring System (PEMS) and loaded to represent a 70% passenger load. Multiple trips were conducted in normal traffic during business hours, stopping at regular bus stops in a similar manner to the passenger service. 

The research found that, when averaged across the bus route on which tests were taken, the total NOx emissions results of the Euro 3 bus retrofitted with SCRT were substantially below those of all of other buses tested, including a Euro 5 hybrid vehicle. 

Meeting tough new standards 

SCRT technology has already been retrofitted to more than 2,500 vehicles. The focus is now moving from buses as old as Euro 2 and 3 to Euro 4 and 5 vehicles. Many operators invested in these vehicles believing they would help to solve pollution problems, but test cycles did not reflect the stop/start reality of urban driving, so most Euro 4s and 5s are not effective in real world urban operation. 

The latest advances in SCRT technology mean it is now possible to upgrade these existing vehicles to Euro 6 standard at significantly lower cost than buying new. Upgraded vehicles can also meet even tougher standards, such as the new London Ultra Low Emission Zone (ULEZ) limits, which will come into force in 2020.

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