Low-temperature dual balance electrodynamic trap (LT-DBET) for single microparticle aerosol studies

Atmospheric aerosol processes regulate our climate through light scattering and cloud formation, which are governed by their physicochemical properties. Despite their climate impacts, important individual particle properties are difficult to measure at controlled temperatures relevant to the troposphere. This study presents the Low-Temperature Dual Balance Electrodynamic Trap (LT-DBET), a commercial DBET from MicroLev LLC, modified with a copper tubing network and a recirculating chiller to achieve temperature control as low as −5 °C, and microdroplet freezing is achieved for droplets loaded with silver iodide. Aerosol microdroplet growth <i>via</i> water uptake is indirectly measured using a feedback loop, which continuously applies balancing voltages proportional to the droplet’s changing mass due to water uptake and release in response to varying RH and temperature. Atmospherically relevant aerosol microdroplet solutes (NaCl, (NH₄)₂SO₄, sucrose, and 2-methyltetrols) are studied. Consistent with previous literature, NaCl exhibits faster water uptake than (NH₄)₂SO₄, and both electrolyte solutions favor dependence on RH for condensational growth over temperature. The presence of 2-methyltetrols in (NH₄)₂SO₄ solution hampers water uptake compared to the single solute (NH₄)₂SO₄ solution. Lowered temperatures decrease the rate of water uptake for sucrose solutions, suggesting that temperature influences organic hygroscopicities more so than electrolytes. This study demonstrates that the LT-DBET provides a robust platform for investigating temperature dependence on other aerosol physicochemical properties, such as surface tension, viscosity, and hygroscopicity, which would improve our understanding of complex aerosol properties and their impacts on climate. The sub-zero temperatures enable studies of processes such as ice nucleation and ice aggregation, using the dual balance.