ABSTRACT Ultrafine particles (UFPs), particularly black carbon (BC), are major contributors to air pollution, climate change, and health risks. Conventional quantification techniques such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Raman Spectroscopy, while effective, suffer from limitations in real‐time analysis, sample representativeness, and scalability. Lock‐in thermography (LIT) has emerged as a promising alternative, offering enhanced sensitivity and real‐time monitoring for nanoparticle detection. In this study, we employ LIT to quantify black carbon. Two measurement configurations—transmission and reflection mode—are utilized to assess spatial distribution and concentration dependence of BC particles collected on filter substrates. Our results demonstrate a strong correlation between measured thermal signals and reference concentrations, confirming LIT's precision in quantifying BC with high reproducibility. The imaging capability further reveals non‐homogeneous particle deposition patterns, which would be challenging to capture using conventional point‐based techniques. These findings establish LIT as a viable tool for real‐time BC quantification in environmental monitoring and industrial applications, overcoming the constraints of traditional measurement approaches.