The cryogenic techniques coupled to spectroscopies (FTIR, UV-visible, …) are powerful tools to study room temperature unstable species (reaction intermediates, unstable isomers, …). Molecules are trapped either in rare-gas matrix or on ice surface in controlled conditions. The low temperature and trapping conditions allow to explore molecular structures and interactions i.e. hydration process from complexes to aggregates and then to ice. Moreover, samples may be kept for long time period (over days) allowing multiple irradiation (selective or broad band) and heating cycles. In this presentation, we will propose two examples of studies related to aerosol of atmospheric interest: the first on the hydration process of 3 methyl-1,2,3-butanetricarboxylic acid (MBTCA), a relevant tracer compound for monoterpene SOA formation and aging processes. The second will focus on the investigation of interactions between gaseous methyl iodine (from marine, vegetation or terrestrial sources) and various water ice surfaces, emphasizing the influence of trapping sites on the bonding and photofragmentation of CH3I. Acknowledgments The authors wish to thank the ANR for financial support of the SOAPHY project (ANR-21-CE29-0031), the Région Nouvelle Aquitaine for it support of the LEVIAERO project (convention n°AAPR2022-2021-17126210) and the GDR EMIE for supporting the collaborative projects.