Nitric acid condensation on ice: 2. Kinetic limitations, a possible ‘‘cloud...

Gamblin, B., O. B. Toon, M. Tolbert, Y. Kondo, N. Takegawa, H. Irie, M. Koike, P. K. Hudson, J. O. Ballenthin, D. E. Hunton, T. M. Miller, A. A. Viggiano, B. E. Anderson, M. Avery, G. Sachse, K. Guenther, C. Sorenson, and M. J. Mahoney (2007), Nitric acid condensation on ice: 2. Kinetic limitations, a possible ‘‘cloud clock’’ for determining cloud parcel lifetime, J. Geophys. Res., 112, D12209, doi:10.1029/2005JD006049.

Measurements of NOY condensation on cirrus particles found in stratospherically influenced air sampled during the SOLVE-I mission are analyzed and compared with data from other field studies of HNO3 or NOY condensation on ice. Each field study exhibits an order of magnitude data spread for constant HNO3 pressures and temperatures. While others assumed this distribution is due to random error, the data spread exceeds instrument precision errors and instead suggests HNO3 removal had not attained equilibrium at the time of sampling. During the SOLVE-I mission, condensation on ice was a significant sink for HNO3 despite submonolayer surface coverages; we therefore propose condensation of HNO3 on lower-stratospheric cirrus particles is controlled by kinetics and will occur at a kinetically limited rate. Furthermore, we suggest the low accommodation coefficient for HNO3 on ice combined with relatively short-lived clouds causes highly scattered, limited HNO3 uptake on cirrus particles. We couple laboratory data on the accommodation coefficient of HNO3 on ice with field surface coverage data in order to generate a ‘‘cloud clock’’: a calculation to determine the age of a cloud parcel. Data from the aforementioned field studies are compared to theoretical models for equilibrium surface coverage on the basis of laboratory data extrapolated to atmospheric temperatures and HNO3 pressures. This comparison is difficult because most of the atmospheric data are probably not at equilibrium and follow a condensation time curve rather than an equilibrium surface coverage curve. Finally, we develop a simple mathematical solution for the time required for HNO3 condensation on ice.

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Upper Atmosphere Research Program (UARP)