Nitric acid condensation on upper tropospheric/lower stratospheric cirrus clouds

Measurements of NOY condensation on cirrus particles during the SOLVE-I field campaign are analyzed and segregated based on altitude. NOY condensation on cirrus particles has different properties depending on whether the ice particles are sampled in the upper troposphere or in the lower stratosphere. Significant amounts of NOY were found on the upper tropospheric ice particles; therefore condensation on ice appears to be an important method of NOY removal from the gas phase at the low temperatures of the Scandinavian upper troposphere. In the lower stratosphere we show that there was less HNO3 measured on the ice particles than those found on the upper tropospheric ice particles. Data collected in stratospherically influenced air sampled during the SOLVE-I mission are then 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 error and instead suggests HNO3 removal had not attained equilibrium at the time of sampling. We propose that 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. Data from the aforementioned field studies are compared to theoretical models for equilibrium surface coverage based upon laboratory data. 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 illustrate it is possible to couple laboratory data of 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.