Abstract Zhao et al. (2025, https://doi.org/10.1029/2024GL112332) state the need for measuring the fractal dimension of black carbon aggregates online and proceed to propose and demonstrate a novel method to derive this fractal dimension from measured mobility parameters and mass concentrations. Their summary of the previous state‐of‐the‐art is that the fractal dimension could not be measured online. Here, we briefly review the literature on the current state‐of‐the‐art for light scattering experiments and clearly establish that optical laboratory measurements of aggregate fractal dimension and size have been performed. Furthermore, we agree with Zhao et al. (2025, https://doi.org/10.1029/2024GL112332) on the importance of developing and utilizing online instruments for such measurements and argue that optical scattering measurements can do so at low cost.