Density and Surface Tension of Aqueous H 2 SO 4 at Low Temperature Cathrine E. L. Myhre, Claus J. Nielsen,* and Ole W. Saastad Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway The density and surface tension of 0.12 to 0.75 acid mass fraction in aqueous sulfuric acid solutions have been measured in the temperature region from (220 to 300) K. The density has been expressed as a polynomial of the acid mass fraction and temperature, fitting the new measurements together with the tabulated values from International Critical Tables (1928). Older literature data for the surface tension of aqueous sulfuric acid has been corrected for systematic errors and used with the new data to derive a parametrization of the surface tension as a function of acid mass fraction and temperature. 1. Introduction Sulfuric acid aerosols are found throughout the lower and middle stratosphere (e.g., Turco et al., 1982; Hoffmann, 1990; Dye et al., 1992; Yue et al., 1994). The composition of the binary system water sulfuric acid may be calculated from the thermodynamic state functions of aqueous sulfuric acid and those of water vapor (Gmitro and Vermeulen, 1961; Zeleznik, 1991; Clegg and Brimblecombe, 1995; Massucci et al., 1996). The actual aerosol composition depends on the local water vapor pressure and tempera- ture, but in addition also upon the density, the surface tension, and the particle size through the Kelvin equation given by Renninger et al. (1981) where r is the radius of curvature, P ∞ is the water vapor pressure over a plane surface, and P r is the water vapor pressure over a curved surface with radius r. M H2O is the molar mass of water, γ the surface tension, T the temper- ature, w the mass fraction sulfuric acid, and F is the density. During our laboratory studies of the physical properties of the stratospheric sulfuric acid aerosols, it became evident that no measurements of the density and the surface tension have been published for temperatures below 273 K. In previous theoretical studies of the sulfuric acid aerosol composition and the Kelvin effect, values for the density and surface tension at low temperatures were by necessity extrapolated from data obtained above 273 K (Doyle, 1961; Nair and Vohra, 1975; Steele and Hamill, 1981, Renninger et al., 1981). The surface tension is also a crucial parameter in the microphysical description of nucleation and homogeneous freezing of sulfate aerosols (Jensen et al., 1991; MacKenzie et al., 1995; Tabazadeh et al., 1997a,b). The density measurements on sulfuric acid were re- viewed and summarized in International Critical Tables (1928); with the exception of a graphical display of the measured density for a solution of 0.36 mass fraction sulfuric acid from 300 K to ca. 220 K (Garrett et al., 1948; Garrett and Woodruff, 1951), no data have appeared since. Several studies of the surface tension have been published, but so far all of the data have not been compared. Different ln ( P r P ∞ 29 ) 2M H 2 O γ RTrF ( 1 + w F ∂F ∂w 29 (1) Table 1. Density at Mass Fractions w of (1 - w) Water + w Sulfuric Acid T/K F/kg m -3 T/K F/kg m -3 w ) 0.123 300 1079.47 276 1089.88 298 1079.86 273 1090.85 297 1080.22 270 1091.77 292 1082.51 269 1092.60 288 1084.16 265 1094.07 284 1085.93 262 1094.57 280 1087.78 w ) 0.291 303 1204.67 263 1232.67 299 1207.32 263 1232.67 294 1211.23 259 1235.90 288 1214.93 250 1242.09 281 1219.84 247 1243.64 270 1227.56 243 1246.01 268 1229.24 241 1246.99 w ) 0.503 301 1391.84 256 1403.67 297 1395.45 246 1438.64 291 1401.95 243 1442.26 284 1406.99 236 1447.33 278 1411.47 229 1452.69 269 1418.86 221 1460.25 262 1425.00 w ) 0.585 302 1473.08 262 1508.49 298 1476.54 252 1517.57 292 1482.20 248 1521.08 286 1487.73 246 1522.96 281 1492.34 241 1528.29 275 1497.20 235 1533.45 269 1502.62 w ) 0.672 303 1569.25 254 1615.08 297 1574.85 248 1619.41 294 1578.04 245 1623.96 290 1581.40 235 1633.93 283 1586.66 230 1639.15 277 1593.49 228 1641.98 265 1604.76 221 1649.67 263 1605.51 w ) 0.765 306 1675.52 261 1719.20 298 1682.20 250 1731.50 297 1682.53 249 1731.85 291 1689.20 243 1738.94 283 1696.60 242 1739.68 277 1702.43 233 1749.83 271 1708.39 617 J. Chem. Eng. Data 1998, 43, 617-622 S0021-9568(98)00013-2 CCC: $15.00 © 1998 American Chemical Society Published on Web 06/05/1998