Assessment of urban co₂ measurement and source attribution in munich based on tdlas-wms and trajectory analysis

Anthropogenic carbon dioxide (CO₂ ) emissions mainly come from cities and their surrounding areas. Thus, continuous measuring of CO₂ in urban areas is of great significance to studying human CO₂ emissions. We developed a compact, precise, and self-calibrated in-situ CO₂ /H₂ O sensor based on TDLAS (tunable diode laser absorption spectroscopy), WMS (wavelength modulation spectroscopy), and VCSEL (vertical-cavity surface-emitting laser). Multi-harmonic detection is utilized to improve the precision of both measurements to 0.02 ppm for CO₂ and 1.0 ppm for H₂ O. Using the developed sensor, we measured CO₂ concentrations continuously in the city center of Munich, Germany, from February 2018 to January 2019. Urban CO₂ concentrations are strongly affected by several factors, including vegetation photosynthesis and respiration (VPR), planetary boundary layer (PBL) height, and anthropogenic activities. In order to further understand the anthropogenic contribution in terms of CO₂ sources, the HySPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model was applied to calculate six-hour backward trajectories. We analyzed the winter CO₂ with the trajectory clustering, PSCF (potential source contribution function), and CWT (concentration weighted trajectory) methods, and found that local emissions have a great impact on urban CO₂ concentration, with main emission sources in the north and southeast directions of the measurement site. In situations with an uneven trajectory distribution, PSCF proves somewhat superior in predicting the potential emission sources compared to CWT.