THE MASS ACCOMMODATION COEFFICIENT OF AMMONIA ON WATER

The mass accommodation coefficient gamma of ammonia gas on water has been determined by measuring the absorption rate of 50-200 ppm NH3 in one atm of air or helium into a liquid jet of 97 mum diameter as function of the exposed jet length, and comparing the results with numerical simulations which treat gamma as the only free parameter. The model considers in detail transport of NH3 by molecular diffusion, penetration of the gas/water interface, hydrolysis in the acidified water, and transport of the solutes from the surface into the jet. A correction is applied for the time evolution of the jet surface speed, using literature data on the fluid mechanics of liquid jets. The result of nine sets of independent measurements is gammNH3 = 0.04(-0.005)+0.03. A sensitivity S = partial-derivativec(aq)/partial-derivative log gamma is defined for mass accommodation measurements by the jet technique. It may be utilized to optimize experimental conditions, and to assign error ranges to measured values of gamma. The atmospheric implications of gammaNH3 = 0.04 are briefly discussed.