(644b) A Semi-Empirical Correlation Between Saturation Concentration and Heat of Vaporization: Application to a Thermodenuder Model

            Current laboratory and atmospheric models that deal with temperature induced re-partitioning of semi-volatile mixtures often assume a constant heat of vaporization for lumped species, or else use specific values for a small set of surrogate compounds.  To improve on this shortcoming, we have developed an easy to implement semi-empirical model to correlate the heat of vaporization (ΔH_VAP) with saturation concentration (C*).  A database of Antoine coefficients was separated into compounds containing only carbon and hydrogen which were used to model primary organic aerosol (POA) and compounds containing only carbon, hydrogen, and oxygen to model secondary organic aerosol (SOA).  These data at relevant temperatures were fit to a thermodynamically derived function relating ΔH_VAP and C* using a non-linear least squares minimization.  These fits allow us to extrapolate the ΔH_VAP vs. C* relationship to compounds that have vapor pressures that are difficult to measure in the laboratory but are commonly present in secondary organic aerosol. Statistical analysis shows that these relationships can be used with enough certainty to improve model accuracy over the current ΔH_VAP treatment.  We have applied the SOA fit to a thermodenuder model to reduce the model uncertainty and to improve model agreement with experimental results.