Ullerstam Maria, Abbatt Jonathan P D
Department of Chemistry, University of Toronto, Toronto, ON M5S 3H6, Canada.
Phys Chem Chem Phys. 2005 Oct 21;7(20):3596-600. doi: 10.1039/b507797d. Epub 2005 Sep 2.
The uptake of gas-phase nitric acid by ice surfaces undergoing growth by vapor deposition has been performed for the first time under conditions of the free troposphere. The investigation was performed using a coated-wall flow tube coupled to a chemical ionization mass spectrometer, at nitric acid partial pressures between 10(-7) and 10(-6) hPa, at 214, 229 and 239 K. Ice surfaces were prepared as smooth ice films from ultra-pure water. During the experiments an excess flow of water vapor was added to the carrier gas flow and the existing ice surfaces grew by depositing water vapor. The average growth rates ranged from 0.7-5 microm min(-1), values similar to those which prevail in some portions of the atmosphere. With growing ice the long term uptake of nitric acid is significantly enhanced compared to an experiment performed at equilibrium, i.e. at 100% relative humidity (RH) with respect to ice. The fraction of HNO(3) that is deposited onto the growing ice surface is independent of the growth rate and may be driven by the solubility of the nitric acid in the growing ice film rather than by condensation kinetics alone.
首次在自由对流层条件下，对通过气相沉积生长的冰表面摄取气相硝酸的情况进行了研究。该研究使用与化学电离质谱仪相连的涂壁流动管，在硝酸分压为10⁻⁷至10⁻⁶ hPa、温度为214、229和239 K的条件下进行。冰表面由超纯水制成光滑的冰膜。在实验过程中，向载气流中加入过量的水蒸气，现有的冰表面通过水蒸气沉积而生长。平均生长速率范围为0.7 - 5微米·分钟⁻¹，与大气中某些部分的普遍值相似。与在平衡状态下（即相对于冰的相对湿度为100%）进行的实验相比，随着冰的生长，硝酸的长期摄取显著增强。沉积在生长冰表面的HNO₃部分与生长速率无关，可能由硝酸在生长冰膜中的溶解度驱动，而非仅由冷凝动力学驱动。
