Fraser McGregor

MODELLING OF SUB-MICROMETER PARTICLE CONCENTRATIONS IN FREE-FLOWING FREEWAY TRAFFIC, BRISBANE, AUSTRALIA: SOME EMPIRICAL RESULTS

As road networks become increasingly more congested, environmental concerns relating to emissions from motor vehicles assume a higher significance. This study found that road side concentrations of particles produced by freeway traffic in Brisbane, Australia, is primarily dependent upon of traffic flow differentiated into fuel type, and wind speed. The analysis differentiates between diesel and petrol vehicles, and finds that particle concentration is very sensitive to the proportion of diesel fuelled vehicles. A 20% increase in diesel vehicles can produce an 18% increase in particle concentrations compared with a 2% particle increase for the same number of additional petrol vehicles.

ESTIMATION OF MOTOR VEHICLE EMISSION FACTORS FROM ROAD MEASUREMENTS OF POLLUTANT CONCENTRATIONS

Motor vehicle emission factors for application in traffic/transport models are often estimated indirectly, through measurements of pollutant concentrations in the close vicinity of a road link. Such an approach provides insight into total vehicle fleet emissions on the link. However, estimation of emission factors form the measured concentration raise a set of complex issues. The concentrations dement not only on the emission factors, but also to a large degree on meteorological factors as well as on the topography of the land. Using the number/mass balance mode, a theoretical relationship was developed that allows for calculation of emission factors from the concentrations measured at a specific point above the road, taking into account wind is the only removal mechanism of the emitted pollutants. By using this model, average emission factors for all vehicles on the road can be estimated and then used to arrive at emission factors for individual types of vehicles, given a known fleet composition. This paper presents an extension of the model to include the effects of humidity and temperature, as well as topographical aspects, on the concentrations measured.

Modelling of Particle Concentration from Motor Vehicles in Urban Environments

Air quality impacts of urban transportation policies and strategies are often assessed using modelling techniques based on traffic flow simulation and travel demand analysis tools. Such analytical methods have traditionally been aimed at estimating the overall mass of individual pollutants with an emphasis on gaseous emissions. Significantly less attention is usually given to the quantification of particle emissions. Extensive data relating to fine and ultra-fine airborne particle concentration levels and the corresponding contributing vehicles have been collected at two significantly different Brisbane sites. Analysis of the relationships between the data so far point to a strong correlation between traffic flow and meteorological variables and particle concentrations. (a) For the covering entry of this conference, please see ITRD abstract no. E206301.