Improving our understanding of aerosol formation, transformation and lifetime in the atmosphere

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Quantifying the partitioning of molecular constituents between the gas and vapour phases is important for understanding aerosols in a broad range of contexts including air quality and the unintentional, intrinsic, or intentional release of aerosolised material. These might include anthropogenic emissions of vapours and particles from cars, the biogenic emissions of organic components in a boreal forest, and the release of vapours and particles from explosive materials, respectively. Not only does phase partitioning govern aerosol particle mass concentrations and size distributions, but it governs the transport of material away from source, and the lifetime and rates of chemical processing and degradation of the source material. Most importantly, this partitioning is dependent on the temperature-dependent vapour pressures of the molecular constituents, their mixing with other aerosol constituents, and the dependence of the partitioning on environmental conditions such as relative humidity (RH). Although of central importance to the whole endeavour of aerosol science, versatile and accurate models of the gas-particle partitioning and component vapour pressures remain largely un-validated. New experiments are required capable of measuring the vapour pressures of components below 1 Pa, representing semi-volatile, low-volatility and extremely low-volatility components. In this project, measurements of the vapour pressures of semi-volatile and low volatility components (1E-6 to 1 Pa) will be made using an electrodynamic balance capable of measuring particle size changes of only a few nanometres on a timescale of hours over wide ranges in RH (<5% to 90%) and temperature (250 to 340 K). Measurements will be made for typical environmental aerosol constituents and surrogates of components, with the ultimate aim of providing an enhanced training set of properties to refine predictive tools for vapour pressures. Measurements will be made with varying conditions (RH and temperature) and with exposure to typical oxidants driving chemical transformation. These improved models will be used in models of gas-particle partitioning, including in transport and box models, to understand the dilution, dispersal and lifetime of aerosol constituents once released from source.