Final Report Summary - FASTER (Fundamental Studies of the Sources, Properties and Environmental Behaviour of Exhaust Nanoparticles from Road Vehicles) Diesel engines emit very large numbers of very small particles referred to as nanoparticles. These particles are believed to make a substantial contribution to the well recognised harmful health effects of diesel exhaust emissions. There is, however, very limited information on the chemical composition of diesel exhaust nanoparticles which is important for two reasons. Firstly, it may influence their toxicity, and secondly it affects their properties in the atmosphere. One of those properties which appears to be quite important is the ability of a large part of the engine exhaust nanoparticles to evaporate from the particles into the vapour phase after emission of particles into the atmosphere. This project has been concerned with sampling the particles, investigating their chemical composition and developing numerical models which predict their behaviour in the atmosphere.A major part of the work is conducted in the engine laboratory where test diesel engines are run with different fuels and lubricating oils and the emissions are collected in order to characterise the composition both of particles and vapours emitted. Chemical composition analysis is conducted in the analytical laboratory both for the particles and the vapour. This allows identification of the major chemical components of the particles and the work has then continued to study some of the key properties of those components. In parallel with these laboratory studies, measurements have been made in the atmosphere which have shown the rates at which particles emitted by road traffic shrink by evaporation, and numerical models have been developed which describe those evaporation processes.There have been a number of major achievements of the project. Firstly, greatly enhanced methods have been developed for identifying the chemical composition of the exhaust particles and vapours. This gives a far better understanding not only of what they are made up from but also how they are derived from the fuel and lubricating oil used in the engine. Our laboratory studies have also produced new values for some of the important properties of the major components of those particles which then allow us to calculate their rates of evaporation in the atmosphere. The atmospheric measurements have been made in central London and give us insights into the rate at which particles evaporate in the atmosphere and thereby change their properties becoming less of a health risk. In order to combine the knowledge gained in the laboratory studies and the field measurements, two kinds of numerical model have been developed. These are computer-based simulations, one of which describes the behaviour of diesel exhaust particles in narrow enclosed streets referred to as street canyons. This is where the highest concentrations tend to exist as well as the largest human exposures. Secondly, the computer models have been extended to a neighbourhood scale of a few square kilometres describing how particle concentrations and size distributions evolve after emission on major highways, as the particles are carried by the atmosphere to downwind locations.
