Secondary organic aerosol (SOA) constitutes a significant proportion of ambient particulate matter and exhibits substantial chemical complexity. The oxidation of a single volatile organic compound (VOC) forms a wide variety of multi-functional oxidation products of differing volatilities. These compounds may undergo numerous oxidation steps, forming a multitude of oxidation products, only some of which may contribute to new particle formation and/or SOA growth. Furthermore, once a compound partitions into the condensed phase it can undergo further oxidation steps and reactive transformations (non-oxidative processes, i.e. oligomerisation), resulting in continually changing chemical composition and volatility. The sheer number of VOCs present in the ambient atmosphere and their continually evolving chemical composition, makes the identification of the species involved in SOA formation, growth and ageing, a complex and difficult task.