Real-World Emission Factors of Fine and Ultrafine Aerosol Particles for Different Traffic Situations in Switzerland

Extended field measurements of particle number (size distribution of particle diameters, D, in the range between 18 nm and 10 μm), surface area concentrations, and PM1 and PM10 mass concentrations were performed in Switzerland to determine traffic emissions using a comprehensive set of instruments. Measurements took place at roads with representative traffic regimes: at the kerbside of a motorway (120 km h-1), a highway (80−100 km h-1), and in an urban area with stop-and-go traffic (0−50 km h-1) regulated by light signals. Mean diurnal variations showed that the highest pollutant concentrations were during the morning rush hours, especially of the number density in the nanoparticle size range (D < 50 nm). From the differences between up- and downwind concentrations (or differences between kerbside and background concentrations for the urban site), “real-life” emission factors were derived using NO x concentrations to calculate dilution factors. Particle number and volume emission factors of different size ranges (18−50 nm, 18−100 nm, and 18−300 nm) were derived for the total vehicle fleet and separated into a light-duty (LDV) and a heavy-duty vehicle (HDV) contribution. The total particle number emissions per vehicle were found to be about 11.7−13.5 × 1014 particles km-1 for constant speed (80−120 km h-1) and 3.9 × 1014 particles km-1 for urban driving conditions. LDVs showed higher emission factors at constant high speed than under urban disturbed traffic flow. In contrast, HDVs emitted more air pollutants during deceleration and acceleration processes in stop-and-go traffic than with constant speed of about 80 km h-1. On average, one HDV emits a 10−30 times higher amount of particulate air pollutants (in terms of both number and volume) than one LDV.