Empa has performed an emissions-comparison study on different power train systems used in 32 automobiles. The study was conducted as part of the investigation to determine emission factors for vehicles used on Swiss roads on behalf of the Swiss Federal Office for the Environment (FOEN). The results, which have just been released, provide valuable, up-to-date comparisons between vehicles which are being marketed today and which meet the current Euro-4 exhaust gas regulations.

The aim of the investigation was to investigate the most important emissions of motor vehicles from the air-pollution point of view. These include fine particulates, ozone-producing gases such as nitrogen oxides and hydrocarbons, and greenhouse gases such as carbon dioxide and methane. The measurements show that all the types of power plants studied – petrol, diesel and natural gas fuelled engines – have become cleaner thanks to the continuous technological developments which have occurred over recent years. An environmentally relevant assessment of these ever-improving vehicles must therefore place more and more emphasis on the greenhouse gas emissions which are responsible for climate change effects. From this point of view natural gas fuelled vehicles, which emit about 21 per cent less greenhouse gases than petrol engines and about 11 per cent less than diesels, still take pride of place.

Despite the technical progress in a general sense, human respiratory problems caused by fine particulates and ozone still remain unsolved, in particular in urban areas. The study shows that diesel vehicles without fine particulate filters produce emission levels about 250 times higher than the other power train systems. The use of diesel particle filters, as called for by FOEN among other bodies, is therefore an important measure in efforts to improve air quality.

In the case of NO_x, which is responsible for ozone production, emissions from petrol and natural gas fuelled engines are at a comparable, low level. Diesel vehicles, on the other hand, give out about ten times more NO_x in comparison. When the proportion of NO₂ in the NO_x is taken into account, even greater differences become apparent. This is particularly important because NO₂ is both an ozone creating agent and a health hazard. While petrol and natural gas engines emit practically no NO₂, with diesel engines the NO_x emissions consist of 30 to 50 per cent of this gas. Diesel vehicles therefore contribute significantly more to local ozone creation than do petrol or natural gas fuelled vehicles.

A relative comparison shows that natural gases emerge as the best option in terms of greenhouse gas and ozone-producing emissions. Petrol fuelled vehicles demonstrate equally good emission of NO_x levels, but with the highest greenhouse gas levels. Diesel vehicles fitted with particle filters show good results in terms of particle emissions (as do petrol and natural gas types), but are at a distinct disadvantage in terms of NO_x emissions. Diesel vehicles not equipped particle filters can only be categorized as “giving cause for concern” due to their high levels of both particulate and NO_x emissions .

The complete study can be downloaded at: www.novatlantis.ch

Further information:
Christian Bach, Internal Combustion Engines, Tel. +41 44 823 41 37, christian.bach@empa.ch