Organic aerosol (OA) forms a major fraction (often well over half) of fine particulate matter in the atmosphere. OA is chemical vibrant, undergoing multiphase chemistry and progressing from chemically reduced emissions to highly oxidized, low volatility material in relatively short order in the atmosphere. In remote regions, highly oxidized OA (OOA) can comprise essentially all of OA. The exact timescale for oxidation is uncertain, but there is considerable evidence that it may be of order 1 day. An additional challenge to understanding this system is that it appears to consist of many thousands of individual organic compounds, forming a mixture consisting of one or two individual phases within and among the suspension of particles in the atmosphere. We have recently developed a framework to describe OA evolution based on volatility and oxidation, using measures of these two properties as independent variables in a two-dimensional space known as the two-dimensional volatility basis set (2D-VBS). We have also recently conducted a number of experiments designed to constrain the role of gas-phase photochemistry in OA oxidation. In this talk we shall consider a number of such systems, viewed through the filter of the 2D-VBS, then consider the broader implications for the OA lifecycle in the atmosphere, focusing especially on the role of organic condensation in the growth of freshly nucleated particles between 1 and 100 nm.