The Growing Challenge of Urban Carbon Emissions

Urban areas cover only about 2% of the Earth’s land surface but are responsible for more than 70% of global CO2 emissions from energy use. As populations continue to concentrate in cities, this share is expected to rise. The concentration of emission sources—power plants, industrial facilities, commercial buildings, and transportation hubs—makes cities both a primary driver of climate change and a critical battleground for mitigation. While renewable energy, energy efficiency, and electrification can reduce emissions substantially, many hard-to-abate sectors such as cement production, waste incineration, and district heating still release large volumes of CO2. For these sources, carbon capture and storage (CCS) offers a direct pathway to net-zero emissions.

However, implementing CCS in dense urban environments presents unique challenges. Space for capture equipment, pipeline routing through crowded underground utility corridors, and the need for safe, permanent storage within reasonable distance all require careful planning. This is where advanced simulation models become indispensable. By integrating geological, engineering, economic, and risk data, these models allow stakeholders to evaluate the potential of urban CCS before committing significant capital.

Understanding Urban Carbon Capture and Storage

Urban CCS involves capturing CO2 directly from large stationary sources within city boundaries or nearby industrial zones. The captured CO2 is compressed, transported, and injected into deep geological formations for permanent storage. Three main capture technologies are deployed in urban settings:

  • Post-combustion capture – Chemical solvents, typically amine-based, are used to separate CO2 from flue gas after combustion. This is the most mature technology and can be retrofitted to existing power plants and industrial facilities.
  • Pre-combustion capture – Fuel is converted into syngas (hydrogen and carbon monoxide), then shifted to produce a concentrated CO2 stream before combustion. Used in integrated gasification combined cycle (IGCC) plants.
  • Oxy-fuel combustion – Fuel is burned in nearly pure oxygen, producing a flue gas that is mainly CO2 and water, which can be separated easily. This approach is less common but offers high capture rates.

For urban environments, post-combustion capture is often the most practical because it can be added to existing facilities without major changes to the combustion process. Once captured, the CO2 must be transported. In dense cities, pipelines are the most efficient option, though they require careful route planning to avoid conflicts with existing underground infrastructure. For cities located near coastlines, ship transport may be an alternative, but it introduces additional logistical complexity.

Storage options typically include deep saline aquifers, depleted oil and gas reservoirs, and, in some regions, basalt formations that mineralize CO2 into stable carbonates. Proximity to suitable storage sites is a key feasibility factor. Simulations must account for the geological characteristics of the storage reservoir, including porosity, permeability, caprock integrity, and the presence of fault lines or legacy wells that could serve as leakage pathways.

The Indispensable Role of Simulation Models

Simulation models provide a virtual laboratory for testing the technical, economic, and environmental aspects of an urban CCS project before any physical intervention. They help answer critical questions: How will the injected CO2 plume migrate over decades to centuries? Will the storage formation maintain its integrity? What is the optimal injection rate to maximize capacity while minimizing pressure buildup? What are the costs under different pipeline routes and capture configurations? And what are the risks of leakage or induced seismicity?

By integrating data from geophysical surveys, well logs, surface infrastructure maps, and emission inventories, simulation models enable multi-scenario analysis. Decision-makers can compare different capture technologies, transport routes, and storage sites to identify the most cost-effective and low-risk combination. Moreover, models can be updated with real-time monitoring data as the project progresses, allowing for adaptive management.

Types of Simulation Models for Urban CCS

Several categories of simulation models are used in assessing urban CCS viability:

  • Geological Reservoir Simulation Models – These models simulate the multi-phase flow of CO2 and brine in the subsurface. They account for processes such as dissolution, trapping, and mineralization. Widely used codes include TOUGH2, Eclipse, and CMG STARS. They require detailed characterization of the reservoir and caprock.
  • Transport and Network Models – These models optimize the pipeline network design, considering source locations, storage sites, terrain, and right-of-way constraints. SimCCS (Scalable Infrastructure Model for CCS) is a prominent open-source tool that combines geographic information system (GIS) data with mixed-integer linear programming.
  • Risk and Leakage Assessment Models – These models evaluate the probability and consequences of CO2 leakage through faults, fractures, or improperly sealed wells. NRAP (National Risk Assessment Partnership) offers a suite of tools for quantifying leakage risks over long time scales.
  • Life Cycle and Economic Models – These models estimate the full cost of a CCS project, including capital, operating, energy penalty, and transport costs. They also assess the CO2 reduction life cycle to ensure that the net climate benefit is real. Integrated assessment models (IAMs) often include CCS as a mitigation option at regional or global scales.

Assessing Urban CCS Feasibility Through Simulation

Multiple simulation-based studies have explored the feasibility of urban CCS in cities around the world. A study simulating CCS for the Tokyo Bay area concluded that injecting into offshore saline aquifers could store more than 100 million tonnes of CO2 over 50 years, but only if pipelines could be routed through densely built-up areas. The study highlighted the trade-off between transport cost and storage capacity, and the model allowed planners to prioritize a phased pipeline expansion.

In the United Kingdom, simulations for the Humber and Teesside industrial clusters—both adjacent to urban populations—demonstrated that retrofitting post-combustion capture on existing plants and shipping CO2 to offshore storage is technically feasible. The models identified the need for extensive monitoring to detect any leakage through legacy boreholes that are common in former industrial areas.

From a geological perspective, not all cities are equally suited for CCS. Cities located above deep sedimentary basins, such as Los Angeles (above the Los Angeles Basin) or Houston (above the Gulf Coast basin), have good potential for onshore storage. In contrast, cities on shallow bedrock or near tectonically active zones may require transport to more distant storage sites. Simulation models incorporate these regional differences to provide realistic assessments.

Key Factors in Feasibility Simulations

  • Storage Capacity and Injectivity – The volume of pore space available and the rate at which CO2 can be injected without exceeding fracture pressure.
  • Containment Integrity – Caprock quality, fault sealing, and the absence of open fractures or abandoned wells.
  • Transport Infrastructure – Distance to storage, existing pipeline corridors, and the cost of new rights-of-way through urban zones.
  • Emission Source Aggregation – Clustering multiple sources to share a single capture and transport system can reduce unit costs.
  • Public and Regulatory Acceptance – While not directly simulated, models can incorporate constraints on injection rates or locations based on policy scenarios.

Challenges and Future Directions

Despite the power of simulation models, practical implementation of urban CCS faces significant hurdles. High capital and operational costs remain the primary barrier. The energy penalty of capture—typically 20–30% for post-combustion amine systems—reduces the net power output of a plant, increasing the cost per tonne of CO2 avoided. Simulation models that incorporate learning curves and technology improvements can help identify future cost breakthroughs, such as new solvents or membrane separation.

Public acceptance is another major challenge. Urban populations often express concern about the safety of underground injection beneath residential areas. Models that visualize the predicted plume migration and demonstrate containment through worst-case scenario testing can build trust. However, effective risk communication is essential; simulations should be transparent and reproducible.

Regulatory frameworks for CO2 storage are still evolving in many jurisdictions. Long-term liability for stored CO2 and requirements for monitoring, reporting, and verification (MRV) are critical issues. Simulation models can inform regulations by quantifying the expected duration of site monitoring needed to confirm stabilization.

Future research is focusing on integrating machine learning with physics-based simulation to accelerate model runs and improve uncertainty quantification. Digital twins—virtual replicas of the entire CCS system updated with real-time sensor data—offer the promise of dynamic optimization over a project’s lifetime. Furthermore, combining urban CCS with direct air capture (DAC) and bioenergy with CCS (BECCS) may offer negative emissions opportunities, though these are less mature and more costly.

Conclusion

Urban carbon capture and storage is not a silver bullet, but simulation models demonstrate that it can play a significant role in helping cities achieve net-zero emissions. By enabling robust feasibility studies, cost optimization, and risk assessment, these models empower decision-makers to pursue CCS projects with confidence. As simulation technology advances and data quality improves, the gap between modeled potential and real-world deployment will narrow. For cities serious about climate action, investing in simulation-based assessment of CCS is a prudent first step toward a low-carbon future.

For further reading, the Global CCS Institute provides comprehensive reports on CCS projects worldwide, while the IPCC Special Report on Global Warming of 1.5°C highlights the role of CCS in mitigation pathways. The U.S. Department of Energy’s Carbon Storage Program offers detailed modeling tools and case studies.