Emission and Pollution Dispersion Model

In order to assess the environmental and climate impacts of the traffic management system in Hefei, the development of an emission and a pollutant dispersion model is necessary.

The emission model allows to calculate traffic emissions (CO, CO2, NOX, SO2, VOC – Volatile Organic Compounds) from the given traffic volume, speed, acceleration and emission characteristics of cars. The transport, dispersion and chemical transformation of these traffic induced emissions will be simulated by means of an Eulerian dispersion model. This model consists of a meso-scale meteorological model, closely coupled with an air chemistry model and a transport model. It allows to estimate consequences of air pollution as well as of pollution reduction measures in the regional (100 km surrounding) scale, far from emission sources.

The current emission model is suited to calculate the above mentioned air pollutants.

Together with the air pollution dispersion model, the effects of the following scenarios to reduce the environmental impacts as well as the emission of the climate gases such as CO2 and water vapor can be investigated:

  • effects of new (e.g. public) transport systems with reduced emissions per passenger,
  • substitution of the traffic fleet by improved catalyst systems,
  • effects of reduced speed limits on different streets.

The following scenarios will influence the Origin-Destination (OD)-Matrix of the traffic zones and, consequently, the emission model cannot be applied directly:

  • the effect of socio-economic changes,
  • the effect of new housing areas or places of work with traffic connections,
  • the effect of environmental zones allowing to enter only vehicles with reduced emissions.

The simulation domain was chosen as an area of 100 km extension in both directions, covering the whole city of Hefei and its surroundings (see figure). Several analysis periods will be chosen to test simulation.

Emission Grid Map

Figure: Simulation domain chosen; source: FU Berlin

In the first steps, immission simulation will be performed mainly on the basis of the traffic emissions and data for the big emitters. This will allow estimation of passive distribution of SO2 and NOX in Hefei and its surroundings. On the basis of these simulations the scenarios (BAU) can be analyzed from the point of view of immission characteristics for SO2 and NOX, their transport and distribution in the area of Hefei. Chemical transfer and ozone formation require a full set of emission data, because air chemistry is a nonlinear process that depends heavily on the relationship of NOX and VOC emissions.

The outputs of the pollution dispersion model will be used to calculate the pollution impacts on the local environment in Hefei. Due to the resolution of the pollution dispersion model, this will be done on a grid size of 500 m x 500 m. This task will answer the question who and what is affected from pollution and emissions in different areas of Hefei. Actual changes in pollution output and dispersion on the local environment will be considered and analysed based on different traffic management scenarios. The impact of technological advantages/disadvantages of transport system changes as well as new traffic management technologies will be considered.