Science. 1995 Jan 20;267(5196):351-5. doi: 10.1126/science.267.5196.351.
Phase changes in stratospheric aerosols were studied by cooling a droplet of sulfuric acid (H(2)SO(4)) in the presence of nitric acid (HNO(3)) and water vapor. A sequence of solid phases was observed to form that followed Ostwald's rule for phase nucleation. For stratospheric partial pressures at temperatures between 193 and 195 kelvin, a metastable ternary H(2)SO(4)-HNO(3) hydrate, H(2)SO(4) . HNO(3) . 5H(2)O, formed in coexistence with binary H(2)SO(4) . kH(2)O hydrates (k = 2, 3, and 4) and then transformed to nitric acid dihydrate, HNO(3) . 2H(2)O, within a few hours. Metastable HNO(3) . 2H(2)O always formed before stable nitric acid trihydrate, HNO(3).3H(2)O, under stratospheric conditions and persisted for long periods. The formation of metastable phases provides a mechanism for differential particle growth and sedimentation of HNO(3) from the polar winter stratosphere.
通过在存在硝酸 (HNO(3)) 和水蒸气的情况下冷却硫酸 (H(2)SO(4)) 液滴，研究了平流层气溶胶的相变化。观察到一系列固相形成，这符合奥斯特瓦尔德相核化规则。对于温度在 193 到 195 开尔文之间的平流层分压，在共存的情况下形成了亚稳三元 H(2)SO(4)-HNO(3)水合物 H(2)SO(4). HNO(3). 5H(2)O、二元 H(2)SO(4). kH(2)O 水合物（k = 2、3 和 4），然后在几个小时内转化为硝酸二水合物 HNO(3). 2H(2)O。在平流层条件下，亚稳 HNO(3). 2H(2)O 总是在稳定的硝酸三水合物 HNO(3).3H(2)O 之前形成，并持续很长时间。亚稳相的形成提供了一种机制，用于从极地冬季平流层中差分粒子生长和硝酸沉降。
