We have been listening to the proposals to discourage ‘dirty diesels’ by cities across Europe, and read with interest the statement from the Society of Motor Manufacturers and Traders (SMMT), speaking up in favour of the diesel car. In our opinion, the evidence from real-on-road tests speaks for itself.
Our research shows Euro 5 standard diesels and earlier are indeed ‘dirty’. They produce high levels of NOx which is harmful to human health. Emissions are particularly bad in urban environments because NOx emissions correlate more closely with incidences of acceleration than speed, thus the stop-start nature of city driving exacerbates air pollution. And, it is made worse by the high number of older diesel buses, taxis and delivery vehicles in the urban environment.
To help combat this problem, the legal limit for NOx emissions was reduced to 0.08g/km with the introduction of the Euro 6 standard for passenger cars, effective from September 2014. We tested a number of the earliest Euro 6 diesels on the market and found that they produced levels of NOx which were seven times above the legislated limits. You can read more about it in the ICCT’s 2014 report, to which EA contributed data.
However, our latest tests show that many newer Euro 6 diesels are showing marked improvements, with NOx levels averaging 2.5 times above the legislated limit. In addition, great strides have been made to clean up new buses and the NOx emissions are now very low from many of these vehicles. Another concern with diesels is the emissions of particulates which are linked to heart and lung disease. However, this issue was addressed with the Euro 5 standard which saw the addition of diesel particulate filters to the exhaust system, which has significantly reduced this problem.
Automotive manufacturers have been investing in NOx abatement technologies and strategies in anticipation of the forth-coming legislative changes which will require an element of real on-road testing, known as Real Driving Emissions. In future it will no longer be sufficient to simply pass the test, manufacturers will also have to demonstrate that their vehicles also comply when driven in the real world.
This can only be to the benefit of urban air quality and thus we agree with the SMMT in that a simplistic ‘demonisation’ of new diesels is not correct. In fact, careful attention needs to be paid to other technologies creating emissions increases, such as direct injection gasoline engines. Nevertheless, there are issues with diesels that are not captured by the regulations, for example the proportion of NOx that is emitted as NO2, the more harmful component. Our research shows that this proportion can be as high as 90% in urban driving, much higher than generally acknowledged.
Emissions Analytics has been leading research in these areas, for example with Imperial College London through the Air Pollution Research in London group, to ensure that the clean-up of diesel engines continues to translate into reality.
NOx in the news
In the press last week was the news that the European Commission has launched legal proceedings against the UK for failing to deal with air pollution. Britain was supposed to meet EU limits set out in the Air Quality Directive by 2010 but the government has said these levels will not be reached until 2020 in most areas and in London it is likely that they will not be met until 2025.
The main cause of these air-borne contaminants regulated by the EU is diesel engines, but why is Britain so far from the target?
A real-world view of NOx
Although auto manufacturers have introduced a number of modifications to meet the ever tightening controls of NOx emissions, a study conducted by Imperial College London and Emissions Analytics, on Euro 5 light-duty diesels, shows the real-world figures exceed Euro 5 standards threefold in most instances.
In the graph above you can see that all the cars in the sample failed to meet Euro standard 4 or 5 and, only three reached Euro standard 3. It can also be seen that the real-world average NOx emissions is considerably higher than the limits set out in the regulations. This is the same situation we see with fuel efficiency when we measure cars for True MPG, comparing their statutory mpg figures to performance in the real world. However, due to high levels of NOx being produced during stop-start driving, such as in traffic, the resulting gap between regulated and real-world air pollution is even more pronounced.
The reasons for Britain breaching EU regulations are many and complex; both NOx and miles per gallon standards are calculated using the New European Drive Cycle, the shortcomings of which have been widely reported and are supported by Emissions Analytics’ large volume of real-world data. Others have voiced concerns regarding the number of monitoring stations and the use of modelled data in EU Air Quality Directive compliance assessments. What it is clear is that real-world data has an important part to play in policy making.
Euro 6 and beyond…
With the introduction of Euro 6 demanding a drop in NOx of 80 per cent on the previous standard, EA and Imperial are continuing their study to see what the impact of this new ruling will be. Emissions Analytics is also developing a new traffic simulation model which will calculate the effect of speed and congestion on fuel economy, as well greenhouse gas (CO2) and air pollution (NOx and CO) components underpinned by the data from its real-world test of more than 400 models of passenger car.