Department of Chemical and Biochemical Engineering, The University of Iowa, Iowa City, IA 52242.
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588.
Proc Natl Acad Sci U S A. 2018 Jun 12;115(24):6147-6152. doi: 10.1073/pnas.1719949115. Epub 2018 May 30.
Ammonia plays a key role in the neutralization of atmospheric acids such as sulfate and nitrates. A few in situ observations have supported the theory that gas-phase NH concentrations should decrease sharply with altitude and be extremely low in the upper troposphere and lower stratosphere (UTLS). This theory, however, seems inconsistent with recent satellite measurements and is also not supported by the aircraft data showing highly or fully neutralized sulfate aerosol particles by ammonium in the UTLS in many parts of the world. Here we reveal the contributions of deep convective clouds to NH in the UTLS by using integrated cross-scale modeling, which includes molecular dynamic simulations, a global chemistry transport model, and satellite and aircraft measurements. We show that the NH dissolved in liquid cloud droplets is prone to being released into the UTLS upon freezing during deep convection. Because NH emission is not regulated in most countries and its future increase is likely persistent from agricultural growth and the warmer climate, the effect of NH on composition and phase of aerosol particles in the UTLS can be significant, which in turn can affect cirrus cloud formation, radiation, and the budgets of NOx and O.
氨在中和大气中的酸（如硫酸盐和硝酸盐）方面起着关键作用。一些现场观测结果支持这样一种理论，即气相 NH 浓度应随高度急剧下降，在对流层顶和同温层下部（UTLS）极低。然而，这一理论似乎与最近的卫星测量结果不一致，也与飞机数据不一致，这些数据显示，在世界许多地区的 UTLS 中，硫酸气溶胶粒子被铵高度或完全中和。在这里，我们通过使用综合跨尺度模型（包括分子动力学模拟、全球化学输送模型以及卫星和飞机测量）来揭示深对流云中对 UTLS 中 NH 的贡献。我们表明，在深对流过程中，液滴中的 NH 溶解在液滴中，在冻结时容易释放到 UTLS 中。由于大多数国家都没有对 NH 的排放进行管制，而且随着农业的增长和气候变暖，其未来的排放量可能会持续增加，因此 NH 对 UTLS 中气溶胶粒子的组成和相的影响可能是显著的，这反过来又会影响卷云的形成、辐射以及 NOx 和 O 的收支。
