Table 11: Description of main variables in stock flow diagram.

Significant variableUnitVariable typeData source

Air pollution charging feeyuan/day·vehicleConstant
Air pollution controlDmnlAuxiliary variableM1+M3
Amount of GDPyuanLevelM1
Amount of motor vehiclesvehicleLevelM1
Amount of motor vehicle tripsvehicleAuxiliary variable
Amount of NOx (PMx) generationtonLevelM1
Amount of populationpersonLevelM1
Annual dissipation of NOx (PMx)ton/yearFlow
Annual scrappedvehicle/yearFlow
Attraction degree of city%ConstantM2
Attraction degree of the growth of vehicles%Auxiliary variableM1+M3
Attraction degree of vehicle trips%Auxiliary variableM1+M3
Birth rate1/yearConstantM3
Contribution rate of NOx (PMx) from vehicle%ConstantM2
Cost of motor vehicle tripsyuan/day·vehicleAuxiliary variableM3
Death rate1/yearConstantM3
Degree of air pollutionDmnlAuxiliary variableM3
Dissipation and control rate of NOx (PMx)1/yearConstantM2
Graphical function of the growth of GDPDmnlAuxiliary variableM3
Growth of GDPyuan/yearFlow
Growth rate of motor vehicles1/yearAuxiliary variableM1+M3
Growth of motor vehiclesvehicle/yearFlow
Growth of populationperson/yearFlow
Growth rate of vehicle ownershipDmnlAuxiliary variableM1+M3
Impact factor of policyDmnlConstantM3
Net migrationperson/yearFlow
Net migration rate1/yearConstantM1+M3
NOx (PMx) emissionston/yearFlow
Per capita annual incomeyuan/personAuxiliary variable
Per vehicle annual of NOx (PMx) emissionston/year·vehicleConstantM2
Pollution degree of NOx (PMx)DmnlAuxiliary variableM1+M3
Population reductionperson/yearFlow
Ratio of motor vehicle trips%ConstantM2
Scrap rate1/yearConstantM2
The average of net migration rate1/yearConstantM1
Weight ratio of PMx (NOx)%Auxiliary variableM3