Measurement of vapor pressures and heats of sublimation of dicarboxylic acids using atmospheric solids analysis probe mass spectrometry.

Vapor pressures of low volatility compounds are important parameters in several atmospheric processes, including the formation of new particles and the partitioning of compounds between the gas phase and particles. Understanding these processes is critical for elucidating the impacts of aerosols on climate, visibility, and human health. Dicarboxylic acids are an important class of compounds in the atmosphere for which reported vapor pressures often vary by more than an order of magnitude. In this study, atmospheric solids analysis probe mass spectrometry (ASAP-MS), a relatively new atmospheric pressure ionization technique, is applied for the first time to the measurement of vapor pressures and heats of sublimation of a series of dicarboxylic acids. Pyrene was also studied because its vapor pressures and heat of sublimation are relatively well-known. The heats of sublimation measured using ASAP-MS were in good agreement with published values. The vapor pressures, assuming an evaporation coefficient of unity, were typically within a factor of ∼3 lower than published values made at similar temperatures for most of the acids. The underestimation may be due to diffusional constraints resulting from evaporation at atmospheric pressure. However, this study establishes that ASAP-MS is a promising new technique for such measurements.