Modelling Motor Vehicle Emissions and Population Exposure in South Australia

Motor vehicle exhaust has been identified as a dominant source of anthropogenic ambient atmospheric pollution. The greatest concentrations of traffic-related air pollution (TRAP) are emitted along heavily trafficked major roadways from which the associated detrimental effects of TRAP exposure have been wellestablished (HEI Panel on the Health Effects of Traffic-Related Air Pollution (2010)). Consequently, populations residing near major roadways have the greatest likelihood of potential exposure to TRAP and a high risk of experiencing adverse health effects. We investigate pollution exposure levels for Adelaide residents in heavily trafficked areas by modelling and simulating TRAP emissions and movement in the atmosphere, with the development of an enhanced Link Emissions Modelling procedure for South Australia. The current Link Emissions Model (CLEM) for South Australia uses emission factors developed overseas and is based on a single average speed. The enhanced Link Emissions Model uses petrol passenger vehicle emissions and vehicle speed data from the second National InService Emissions study, to derive new Australian emission factors for use in South Australia. The result is the petrol passenger vehicle Link Emissions Model, PLEM. In essence, PLEM is an augmented version of CLEM, however provides the advantages of accommodating a range of vehicle speeds and is based on Australian data. The enhanced Link Emissions Modelling procedure for South Australia estimates road link TRAP emissions through the use of PLEM for petrol passenger vehicles in conjunction with CLEM for all other vehicle types. The enhanced Link Emissions Model is implemented in a case study of selected densely trafficked roadways near residential areas of Adelaide, South Australia, to assess population TRAP exposure levels and the current air quality status in Adelaide. Vehicular exhaust emissions are estimated for each road link in the case study area using the enhanced Link Emissions Model. The Air Pollution Model (TAPM), an air quality tool for pollution dispersion, is used to analyse the movement of the link emission estimates in the atmosphere with pollution exposure maps showing approximate pollution concentrations for the case study region, generated by combining TAPM output with Geographic Information Systems data. Results of the case study indicate that TRAP concentrations are greatest over main roads and their intersections, with pollutant concentrations declining with increasing distance from the main roads. Pollution concentrations fluctuate across the week, with each day typically experiencing two peaks in air pollution concentrations corresponding to peak traffic hours. The lowest pollution concentrations occur during the early hours of a day when traffic volumes are typically lowest. Furthermore, the results suggest TRAP concentrations are subject to seasonal variation with the greatest concentrations occurring during the calm, cold weather conditions of winter and the lowest concentrations occurring during the windy, warm summer season. Atmospheric vehicle exhaust pollution concentrations in the case study area of Adelaide are comfortably below the threshold levels specified by the World Health Organisation however Adelaide residents are exposed to a notable volume of vehicular exhaust pollution. Thus mitigation strategies for TRAP emission and exposure should be designed and implemented for South Australia. The case study results indicate use of the enhanced Link Emissions Model provides a strong understanding of approximate pollution concentrations in the Adelaide air shed, forming a solid platform upon which to base future informed strategies for emission reduction and exposure mitigation.