Sarin

CAS RN: 107-44-8

Volatilization

The Henry's Law constant for sarin is estimated as 5.7X10-7 atm-cu m/mole(SRC) derived from its vapor pressure, 2.86 mm Hg at 25 deg C(1), and water solubility, and assigned value for water solubility of 1.0X10+6 mg/L (miscible)(2). This Henry's Law constant indicates that sarin may volatilize slowly from water surfaces(3). It has been shown that the vapors above a water solution at 25 deg C containing 140 ug/L sarin will contain 0.0004 ug/L sarin(1) which demonstrates an ability to volatilize slowly from water(SRC). Based on the Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(3) is estimated as 76 days(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(3) is estimated as 555 days(SRC). With hydrolysis half-lives on the order of 24 to 237 hours at 25 deg C(4), hydrolysis will attenuate any importance of volatilization from water(SRC). The potential for volatilization of sarin from dry soil surfaces may exist based upon its vapor pressure(SRC). Under ordinary atmospheric conditions, sarin has sufficiently high volatility to permit evaporation into air(5). At 10 deg C, the time required for 90% of 1-mm-diameter droplets of sarin to evaporate from non-absorbing surfaces is only 0.24 hr(6); at 0 deg C and -20 deg C, the evaporation times are 0.58 hr and 1.8 hr, respectively(7). In field studies in Norway using snow, 55% of applied sarin was removed by evaporation within 5 hours(4).
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