has not yet been unambiguously identified in aerosol research. Kulmala et al. partitioned the NPF process into three regimes and suggested the critical size for clustering to occur between 1.1 nm and 1.9 nm. While this may seem like a narrow range, the number of molecules in the cluster can range from a handful to hundreds in this size range. To this date, no single technique is able to capture the entire route from single molecules to clusters, ending up as aerosol particles. However, advanced mass spectrometer techniques, such as the CI-APi-TOF, have been used to give insight into the chemical composition during clustering.