<div class="htmlview paragraph">Major part of the research work on particulate emissions has been carried out at normal ambient temperature (about +23 °C). In real life, the average day temperatures, especially in the winter season, are far below the “normal” temperature of the exhaust emission test procedures. For many years, it has been obvious that the knowledge of the total particulate mass emissions is not enough. Quality of these particles, e.g. polyaromatic hydrocarbon content and mutagenicity, has been studied. Now there is also a need to gain more information on fine particles, which can penetrate lungs more easily. International Energy Agency's Committee on Advanced Motor Fuels sponsored this study of the possible effect of ambient temperature on particle emissions. Also aldehydes and speciated hydrocarbons were studied.</div> <div class="htmlview paragraph">Several different engine and fuel technologies were covered, including gaseous fuels and biodiesel. Research work focused on light-duty technologies. Test vehicles were as follows: two diesel cars (direct and indirect-injection), stoichiometric gasoline fuelled car (multi-port-fuel-injection), direct-injection gasoline car, Flexible Fuel Vehicle running with E85 fuel, CNG and LPG cars. Four diesel fuel qualities were studied: European grade diesel fuel (EU2000), a blend of this fuel and 30% rape seed methyl ester (RME30), Swedish Environmental Class 1 fuel (RFD) and a blend of this fuel and 30% RME (RFD/RME).</div> <div class="htmlview paragraph">The effect of temperature was dependent on the engine technology. Significant increase in particle mass and number emissions was seen with some technologies when -7 °C temperature was compared to normal test temperature. Some engine technologies were rather insensitive to ambient temperature, e.g. CNG car did not show any significant particle emission at normal or low temperatures. If an increase in particle emissions was seen, it typically appeared immediately after the cold start. With the warmed-up engine the particle emissions were mainly at the same level at normal and low temperatures. In some cases RME indicated more particles and/or a shift to lower mean diameter at low temperatures after the cold start than in the tests at normal temperature.</div>