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Sea spray aerosols contain a large array of organic compounds that contribute to high viscosities at low relative humidity and temperature thereby slowing translational diffusion of water. The Stokes-Einstein equation describes how viscosity is inversely correlated with the translational diffusion coefficient of the diffusing species. However, recent studies indicate the Stokes-Einstein equation breaks down at high viscosities achieved in the particle phase (>10 12 Pa·s), underestimating the predicted water diffusion coefficient by orders of magnitude and revealing the need for directly studying the diffusion of water in single aerosol. A new method is reported for measuring the water diffusion coefficient in single suspended charged sucrose-water microdroplets in the 30-60 micron diameter range. The translational water diffusion coefficient is quantified using H 2 O/D 2 O isotope exchange technique between 26-54% relative humidity (RH) with a recently developed mobile electrodynamic balance apparatus. The results are in good agreement with literature, particularly the Vignes-type parameterization from experiments using isotope exchange and optical tweezers. This mobile electrodynamic balance will allow future studies of atmospherically relevant chemical systems, including field studies.