We report temperature (T = +22.5 similar to -57.0 degrees C)-controlled optical trapping of single dimethylsulfoxide (DMSO) droplets with the diameter (d) of 7-15 mu m in air. Optically levitated DMSO microdroplets containing 0.1 mol/dm(3) (=M) potassium iodide (KI) as an additive for reducing the vapor pressure of DMSO in air have been suggested to take supercooled liquid states even below the freezing temperature (f(p)) of the bulk DMSO liquid (f(p) = +18.4 degrees C in the presence of 0.1 M KI) as seen in bright-field microscopic observations of the droplet. Clear evidence for supercooling of an aerosol DMSO microdroplet below f(p) has been obtained by in situ optical trapping-polarized Raman microspectroscopy of the droplet down to -14.9 degrees C. Analysis of the polarized Raman spectral data of an aerosol DMSO droplet (d = similar to 10 mu m) has demonstrated that the droplet at +22.5, +0.2, or -14.9 degrees C is characterized by the rotational relaxation time (tau(rot)) of a DMSO molecule in the droplet being 1.95, 2.58, or 3.90 ps, respectively. On the basis of the tau(rot) values and the Stokes-Einstein equation (tau(rot) = 8 pi a(3) eta/k(B)T where a, eta, k(B) are the radius (1.883 angstrom) of a DMSO molecule, the viscosity in DMSO, and the Boltzmann constant, respectively), the eta values in the DMSO microdroplet in air at +22.5, +0.2, or -14.9 degrees C have been estimated to be 2.39, 2.94, or 4.20 cP, respectively, while that of bulk DMSO liquid at +20.5 degrees C is 1.98 cP. We also report the T-dependence (+22.5 > T > -14.9 degrees C) of the viscosity in a single aerosol DMSO microdroplet (d = similar to 10 mu m) and the effects of aerosolization in air on the viscosity in DMSO.