Department of Physics, University of Helsinki, Helsinki, Finland.
Phys Rev Lett. 2011 Jun 3;106(22):228302. doi: 10.1103/PhysRevLett.106.228302. Epub 2011 Jun 1.
Sulfuric acid is a key compound in atmospheric nucleation. Here we report on the observation of a close-to-collision-limited sulfuric acid dimer formation in atmospherically relevant laboratory conditions in the absence of measurable quantities of ammonia or organics. The observed dimer formation rate was clearly higher than the measured new particle formation rate at ∼1.5 nm suggesting that the rate limiting step for the nucleation takes place after the dimerization step. The quantum chemical calculations suggested that even in the ultraclean conditions there exist (a) stabilizing compound(s) with (a) concentration(s) high enough to prevent the dimer evaporation. Such a stabilizing compound should be abundant enough in any natural environment and would therefore not limit the formation of sulfuric acid dimers in the atmosphere.
硫酸是大气成核的关键化合物。在这里，我们报告了在大气相关的实验室条件下，在没有可测量量的氨或有机物的情况下，接近碰撞限制的硫酸二聚体形成的观察结果。在约 1.5nm 处，观察到的二聚体形成速率明显高于测量到的新粒子形成速率，这表明成核的速率限制步骤发生在二聚化步骤之后。量子化学计算表明，即使在超净条件下，也存在（a）稳定化合物（s），其（a）浓度（s）足以高到防止二聚体蒸发。这样的稳定化合物在任何自然环境中都应该足够丰富，因此不会限制大气中硫酸二聚体的形成。
