A two-dimensional volatility basis set – Part 2: Diagnostics of organic-aerosol evolution
We discuss the use of a two-dimensional volatility-oxidation space (2-D-VBS) to describe organic- aerosol chemical evolution. The space is built around two coordinates, volatility and the degree of oxidation, both of which can be constrained observationally or specified for known molecules. Earlier work presented the thermodynam- ics of organics forming the foundation of this 2-D-VBS, al- lowing us to define the average composition (C, H, and O) of organics, including organic aerosol (OA) based on volatility and oxidation state. Here we discuss how we can analyze ex- perimental data, using the 2-D-VBS to gain fundamental in- sight into organic-aerosol chemistry. We first present a well- understood “traditional” secondary organic aerosol (SOA) system – SOA from α-pinene+ozone, and then turn to two examples of “non-traditional” SOA formation – SOA from wood smoke and dilute diesel-engine emissions. Finally, we discuss the broader implications of this analysis.