The nucleation of low-volatility vapors to molecular clusters and the growth of these initial clusters to macroscopic particles, a process called new particle formation (NPF), is the largest source of atmospheric aerosols with respect to their number. Therefore, this process is important for the global climate as well as local air quality [1]. While inorganic acids mostly drive nucleation, it is also well-known that organic molecules contribute significantly to NPF. However, it is unknown at what stage in NPF organic compounds become important, or whether they can efficiently nucleate in the absence of inorganic acids [2]. This knowledge gap arises partly because NPF is usually investigated by mass spectrometry, which provides only compositional, not structural, information. Here, we show that matrix isolation Fourier transform infrared spectroscopy (MI-FTIR) is a versatile tool for studying the formation of atmospheric organic aerosols. It was previously demonstrated that MI-FTIR is a reliable tool to study clusters of small, atmospherically relevant molecules [3]. Here, we extend this approach to larger organic molecules important for NPF, such as pinic and pinonic acid. Freezing these molecules in inert noble gas matrices at 6 K, followed by subsequent annealing at 30-40 K, enables the study of the formation of initial molecular clusters, such as dimers (see Fig. 1). Comparing the resulting spectra to calculations based on density functional theory makes it possible to distinguish between dimer conformers being more beneficial for further growth due to free OH-groups and dimer conformers that cannot grow further. This provides valuable insights into potential growth pathways for atmospheric organic aerosols. In a second experiment, grown aerosol particles are loaded onto filters, which are then introduced into the matrix. It is demonstrated that this approach makes it possible to identify dominant functional groups in grown particles. By pre-selecting different particle sizes, we plan to investigate which functional groups dominate the growth of aerosols in which size regime and, by that, use our MI-FTIR setup to bridge yet another gap in NPF research.