Mobility Modelling
Lecture 8 - Emission Modelling
3 April 2023
Mozhgan Pourmoradnasseri, Ph.D.
Share of co2 emission
The CO2 emissions from burning fossil fuels represent the primary contribution of the transportation field.
Le Quéré, C., et.al. (2020). Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement. Nature climate change, 10(7), 647-653.Air pollution generated by vehicle emissions has become increasingly evident, to the point that the temporary interruption of regular traffic during the COVID-19 lockdowns resulted in a tremendous decrease in CO2 emission.
Quantifying vehicle emissions
- A small sample of vehicles, high spatiotemporal, portable sensors, in real-world driving conditions.
- An entire fleet in a region, from odometer readings and traveled distance in annual inspections.
- Based on traffic flow models.
- Based on GPS tracks.
Estimating CO2 Emissions from IoT Traffic Flow Sensors
Bilotta, S., & Nesi, P. (2022). Estimating CO2 Emissions from IoT Traffic Flow Sensors and Reconstruction. Sensors, 22(9), 3382.
Emission sensors
Traffic sensors
An example of a CO2 heatmap in Florence Municipality
- Relies on macroscopic traffic model.
- Aggregated data.
- Discurds the contribution of other sectors to CO2 emission measured by sensors.
Böhm, M., Nanni, M., & Pappalardo, L. (2022). Gross polluters and vehicle emissions reduction. Nature Sustainability, 5(8), 699-707.- Used trajectories produced by onboard GPS devices to compute the vehicle emissions and matched the obtained emissions to the cities’ road networks.
- GPS trajectories describing 423,018 trips from 16,715 private light-duty vehicles moving in Greater London, Rome, and Florence throughout January 2017.
- Microscopic emissions model that uses speed, acceleration and fuel type to estimate the instantaneous vehicle emissions of CO2, nitrogen oxides (NOx), particulate matter (PM) and volatile organic compounds (VOC).
Gross polluters and vehicle emissions reduction
step-by-step procedure for the estimation of the vehicles' emissions
Now, whether we have the information about each vehicle's engine type or not, we can exploit this information together with a table with emissions functions to estimate the vehicles' instantaneous emissions at each point, with the module emissions.
The method is applied to GPS tracks in three cities that are heterogeneous in their road networks:
- Rome is large, but with the sparsest network;
- London is huge, but with the densest network;
- Florence is small (~1/12 of Rome and ~1/15 of London in terms of land area), but with a dense road network.
- The top 10% of gross polluters in Florence, Rome and London were responsible for 47.5, 50.5 and 38.5% of the total CO2 emitted during the month, respectively.
- A few grossly polluted roads suffered from a substantial quantity of emissions, most of the roads suffered substantially fewer emissions.
- In Florence and Rome, the top 10% of grossly polluted roads are associated with more than 90% of the CO2 emitted during the period. In London, this quantity is lower (56.7%), but still more than half of the city’s total emissions of CO2.
results
The radius of gyration indicates the characteristic distance traveled by an individual.
The mobility entropy characterizes the predictability of their visitation patterns.
The total travel time of the vehicles is a principal factor governing emissions.
Relationship with mobility and road features
- The observed negative correlations between entropy and emission suggest that gross polluters are more regular and predictable than low-emitting vehicles.
- By performing a cluster analysis to group vehicles based on their radius of gyration, mobility entropy and travel time, two clusters are found, namely the predictable and erratic drivers, and found that the former emit typically more than the latter.
Impact on CO2 emissions of the electrification of the vehicles moving within a neighborhood in Rome.
- The greenhouse gas emissions footprint and global warming potential are widely used for environmental sustainability studies. However, environmental sustainability is far wider than carbon emissions and climate change.
- The global concern of anthropogenic emission has been principally focused on GHG compared to air pollutants. GHG are subject to global agreements and taxation, whereas air pollutants are governed by local legislation and policy.
Van Fan, Y., Perry, S., Klemeš, J. J., & Lee, C. T. (2018). A review on air emissions assessment: Transportation. Journal of cleaner production, 194, 673-684.GHG vs. air pollutants
Air pollutants
Van Fan, Y., Perry, S., Klemeš, J. J., & Lee, C. T. (2018). A review on air emissions assessment: Transportation. Journal of cleaner production, 194, 673-684.Air pollutants such as carbon monoxide (CO), contaminants (e.g. Pb), volatile organic compounds (VOCs), sulphur oxide (SOx) and nitrogen oxide (NOx) (EPA, 2016) have an instantaneous impact on the environment and human health.
GHG emission by source sector in the US, 2015
The pollutant emission comparison by source sector in the US, 2014
The sources of emission from transportation and the shares of shipping (transport of goods by water transport).
GHG emissions by sources from the transport and non-transport sector in the EU
Emission measurement
Even having the identical place of departure and arrival, the distance/route traveled by truck, rail and ship are different. The contrasting results suggest the complexity of assessing the non-stationary source of emissions and challenges in defining a sustainable freight transport mode. The truck has a better performance in terms of PM10 and NOx, but the ship has lower CO2eq and SO2 emissions. This highlights the importance of simultaneous assessment of GHG and air pollutants for proper decision-making, as low GHG emissions do not represent low emissions for other pollutants.
- The question remains in the conflict situation, for example, to select a solution with lower CO2 (GHG) emission or lower SOx (air pollutants) emission?
- How to achieve a feasible (cost, time, etc.) freight transport mode or system with low air emission?