Model simulation of ultrafine particles inside a road tunnel

A monodispersive aerosol dynamic model, coupled to a 3D hydrodynamical grid model, has been used to study the dynamics of ultrafine particles inside a road tunnel in Stockholm, Sweden. The model results were compared to measured data of particle number concentrations, traffic intensity and tunnel ventilation rate. Coagulation and depositional losses to the tunnel walls were shown to be important processes during traffic peak hours, together contributing to losses of 77% of the particles smaller than 10nm and 41% of the particles of size 10-29nm. Particle growth due to water uptake or the presence of a micron-sized, resuspended particle fraction did not have any significant effect on the number of particles lost due to coagulation. Model simulation of particle number concentration response to temporal variations in traffic flow showed that constant emission factors could be used to reproduce the concentration variations of the particles larger than 29nm, while vehicle-speed-dependent factors are suggested to reproduce the variation of the smallest fractions. The emission factors for particle number concentrations estimated from the model simulation are in general higher and show a larger contribution from light-duty vehicles than what has been reported from a tunnel in California. The model study shows that combined measurements and model simulations in road tunnels can be used to improve the determinations of vehicle emission factors for ultrafine particles under realistic driving conditions. (C) 2003 Elsevier Science Ltd. All rights reserved

Real-world traffic emission factors of gases and particles measured in a road tunnel in Stockholm, Sweden

Measurements in a road tunnel in Stockholm, Sweden give the real-world traffic emission factors for a number of gaseous and particle pollutants. These include 49 different polycyclic aromatic hydrocarbons (PAH), CO, NOX, benzene, toluene, xylenes, aldehydes, elements and inorganic/organic carbon contained in particles, the sub-micrometer aerosol number size distribution, PM2.5 and PM10. The exhaust pipe emission factors are divided with the help of automated traffic counts into the two pollutant sources, the heavy-duty vehicles (HDV) and light-duty vehicles (LDV). The LDV fleet contains 95% petrol cars and the total fleet contains about 5% HDV. When data permitted, the emission factors were further calculated at different vehicle speeds. The current work shows that average CO, NOX and benzene emission factors amounted to 5.3, 1.4 and 0.017 g veh(-1) km(-1), respectively. Since the mid-90s CO and benzene decreased by about 15%, carbonyls by about a factor 2, whereas NOX did not change much. PAR emission factors were 2-15 times higher than found during dynamometer tests. Most particles are distributed around 20 nm diameter and the LDV fleet contributes to about 65% of both PM and particle number. In general, the gaseous emissions are higher in Sweden than in USA and Switzerland, foremost due to the lower fraction catalytic converters in Sweden. The PM and number emissions of particles are also slightly higher in the Swedish tunnel. (C) 2003 Elsevier Ltd. All rights reserved

Risk of Air Pollution in Relation to Cancer in the Nordic Countries

Seventeen pollutants (particles, heavy metals, inorganic gasses and organic compounds) are for the first time analyzed in a screening of the carcinogenic risk at very high resolution and large scale in ambient air in the Nordic countries. Modelled 2010 annual mean air concentrations show no exceedances of the EU air quality values. The only exceedance of US-EPA 1:100,000 cancer risk concentrations occurs for the PAH BaP in Denmark. However, the EU target value threshold for BaP is not exceeded. No emission data for BaP are available for the other countries and important uncertainties are still related to the Danish emissions. Long-range transport is significant except for BaP that originates mostly from residential wood combustion. It is recommended to monitor the influence from residential wood combustion more extensively, and to analyze longer time trends for long-term human exposure