Bottom-up estimation of traffic emissions in Munich based on macroscopic traffic simulation and counting data

Cities are home to more than half of the world’s population, a share that will continue to grow in the future and account for more than 70% of the global fossil fuel CO₂ emissions. To avoid dangerous climate change, cities will be required to reduce their energy consumption and cut carbon emissions significantly. Emission inventories are the basis for any carbon mitigation efforts. They determine the current status, allocate emissions to various sectors and indicate their reduction potential. The ICOS-Cities project fosters this development and aims to set up integrated city observatories in three pilot cities (Paris, Zurich and Munich). Reliable prior data is essential for modeling efforts in this project and road transport is a key emission sector in urban areas.

We present a newly developed, highly spatially and temporally resolved bottom-up traffic emission inventory for the area of Munich (311 km²), covering outer circle motorways as well as inner city roads. The inventory accounts for greenhouse gases (CO₂, CH₄) and co-emitted species/ air pollutants (CO, NO₂, O₃ and PM). It has a temporal resolution of one hour and is compiled for the years 2019 to 2022. The emissions are represented as line sources along the road network, which allows for emission sampling ranging from several tens of meters in densely interconnected inner-city environments to a kilometer-scale on highways.

The inventory is based on the city’s official macroscopic traffic model (VISUM), which we validate using traffic counts from more than hundred permanent traffic monitoring stations in Munich since this data is not implemented in the traffic model. Additionally, we extrapolate the traffic model to unobserved days (e.g., weekends, holidays) by means of traffic counts, and distinguish between vehicle classes (private car, heavy duty vehicle, light duty vehicle, coach and motorbike) based on categorized traffic counts. HBEFA emission factors (Handbook for Road Transport Emission Factors) are applied to estimate the emissions.

A comparison with the official emission numbers of the City of Munich and other spatially explicit inventories available in the same region, such as TNO GHGco database, is conducted. We will present the main discrepancies and provide insights for other cities aiming to develop similar inventories.