Characterisation of Exhaust Particulate Emissions from Road Vehicles
Health effects of particulate emissions from road transport have been of interest for many years. Historically, particulate emissions from road vehicles have been controlled and progressively reduced through legislation based on particulate mass measurement. More recently, interest has extended into more specific characteristics of particle emissions such as size, number, surface area and composition.
PARTICULATES was 3.5 year project launched in April 2000 as a common project cluster with ARTEMIS. It was launched under the 'Competitive and Sustainable Growth' Programme of the European Commission's Fifth Framework Programme for research (FP5) and was funded by the Directorate-General for Energy and Transport (Contract No. 2000-RD.10429).
The project involved 22 partners from nine European Countries and involved two external consultants from USA and Austria. The Laboratory of Applied Thermodynamics in the Aristotle University Thessaloniki acted as the project coordinator. The 'PARTICULATES' Consortium was established to develop further knowledge on particulate emissions from motor vehicles, including characterisation of particulate size and number emissions, with current and future vehicles and fuels.
The main aims of 'PARTICULATES' were:
- to increase understanding of particulate emissions from road vehicles,
- to provide a harmonised particulate sampling and measurement methodology,
- to provide input on representative emissions factors for particulates to enhance air quality modelling tools,
- to assess the effectiveness of technical measures for reducing particulate emissions.
In the 'PARTICULATES' project, it was decided to study both the 'accumulation mode' and the 'nucleation mode' particles under transient and steady-state conditions. A harmonised sampling and testing methodology was developed. This was deployed in several laboratories to assess the effects of different vehicle technologies, fuels and operating conditions. The work was completed by some vehicle case studies, tunnel studies and non-exhaust emissions measurements.
Light-duty diesel vehicles and heavy-duty diesel engines equipped with particulate traps produced very low particulate emissions (mass and number) when operating on low sulphur fuels. A heavy-duty prototype Euro-5 engine using SCR/urea NOx after-treatment without a particle trap, produced very low particulate mass emissions, within Euro-5 limits, but its particle number emissions were higher than the DPF-equipped option. The effect of diesel fuel sulphur was most evident under high temperature operation. Under these conditions, fuels with nominal 50ppm or less sulphur gave significant reductions in particle mass and number emissions versus 300ppm sulphur fuels. In the advanced engine technologies, fuel effects on particulate emissions (other than sulphur) were small in absolute terms. Direct injection gasoline cars produced measurable amounts of particulate mass emissions, well below the Euro-4 diesel vehicle emissions limit, but higher than conventional gasoline cars and DPF-equipped diesel cars. This was reflected in the numbers of carbonaceous
and total particles.
- Particle number measurement techniques offer the potential for greater measurement sensitivity and discrimination, and are especially valuable for further research into cleaner vehicles and fuels.
There is some evidence that the number of 'solid' particles does not always correlate with mass. However, further methodology development, including definition of suitable instrument calibration procedures and multi-lab validation, would be required
prior to use of 'solid' particle number measurements in regulation.
- Developments in particle emissions performance of direct injection gasoline cars should be closely monitored.
- The relevance of the NEDC emission test cycle to real world operation should be reviewed.
- Further research continues to be needed on the health relevance of measurements of 'nucleation' mode particles, their chemical composition and their fate in the atmosphere.
- A major step in particulate emission control will be taken through the combination of diesel particulate filters and sulphur-free (10 mg/kg max S) fuels.
- Particle mass measurement is capable of distinguishing between engine technology levels up to DPF-equipped systems. Its continued use in regulation has the advantage of providing continuity with previous data