Knopf Daniel A
Institute for Atmospheric and Climate Science, IAC, Zürich, Switzerland.
J Phys Chem A. 2006 May 4;110(17):5745-50. doi: 10.1021/jp055376j.
Laboratory data of the freezing of nitric acid hydrates (NAD, NAT) from HNO(3)/H(2)O and HNO(3)/H(2)SO(4)/H(2)O solution droplets have been evaluated with respect to a "pseudoheterogeneous" (surface-induced) nucleation mechanism of NAD and NAT, which has been argued to possibly lead to the formation of polar stratospheric clouds (PSCs). In addition, a parametrization of pseudoheterogeneous nucleation of NAD and NAT suggested recently (Tabazadeh et al. J. Phys. Chem. A 2002, 106, 10238-10246) has been analyzed, showing that this parametrization should not be used in stratospheric modeling studies. The analysis of several laboratory data sets yields an upper limit of the pseudoheterogeneous nucleation rate coefficient of NAD of 2.2 x 10(-5) cm(-2) s(-1). In contrast, the upper limit of the pseudoheterogeneous nucleation rate coefficient of NAT could not be constrained satisfactorily, since formation of NAT has not been observed at stratospheric conditions in laboratory experiments applying small droplets. Maximum NAD production rates of 9.6 x 10(-9) cm(-3) (air) h(-1) in the stratosphere have been estimated assuming a pseudoheterogeneous nucleation mechanism that is constrained by the experimental observations. If maximum NAD supersaturation persisted for 4 weeks in the polar stratosphere the corresponding NAD particle number densities are estimated to be about 6 x 10(-6) cm(-3). These particle number densities are 3 orders of magnitude lower than particle number densities recently observed in the stratosphere. In conclusion, on the basis of laboratory data it is found that a pseudoheterogeneous nucleation mechanism is not sufficient to explain recent observations of large nitric acid containing particles in the polar stratosphere.
针对硝酸水合物（NAD、NAT）从HNO₃/H₂O和HNO₃/H₂SO₄/H₂O溶液滴中冻结的实验室数据，已根据NAD和NAT的“假非均相”（表面诱导）成核机制进行了评估，有人认为该机制可能导致极地平流层云（PSC）的形成。此外，最近提出的NAD和NAT假非均相成核的参数化方法（Tabazadeh等人，《物理化学杂志A》2002年，106卷，10238 - 10246页）已被分析，结果表明该参数化方法不应在平流层模型研究中使用。对多个实验室数据集的分析得出，NAD假非均相成核速率系数的上限为2.2×10⁻⁵ cm⁻² s⁻¹。相比之下，NAT假非均相成核速率系数的上限无法得到令人满意的限制，因为在应用小液滴的实验室实验中，未在平流层条件下观察到NAT的形成。假设受实验观测约束的假非均相成核机制，已估算出平流层中NAD的最大生成速率为9.6×10⁻⁹ cm⁻³（空气）h⁻¹。如果在极地平流层中最大NAD过饱和度持续4周，相应的NAD粒子数密度估计约为6×10⁻⁶ cm⁻³。这些粒子数密度比最近在平流层中观测到的粒子数密度低3个数量级。总之，基于实验室数据发现，假非均相成核机制不足以解释最近在极地平流层中观测到的含大量硝酸粒子的现象。
