Zheng Guangjie, Su Hang, Cheng Yafang
Minerva Research Group, Max Planck Institute for Chemistry, Mainz 55128, Germany.
Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.
ACS Environ Au. 2022 May 6;2(4):346-353. doi: 10.1021/acsenvironau.1c00055. eCollection 2022 Jul 20.
Acidity is one essential parameter in determining the aqueous phase physical and chemical processes in the atmosphere and strongly influences the climate, ecological, and health effects of aerosols. Traditionally, aerosol acidity is thought to increase with emissions of atmospheric acidic substances (SO, NOx, etc.) and decrease with that of alkaline ones (NH, dust, etc.). However, decade-long observations in southeastern U.S. seem to disagree with this hypothesis: while the emissions of NH versus SO enhanced by over three times, the predicted aerosol acidity is stable, and the observed particle-phase ammonium-to-sulfate ratio is even decreasing. Here, we investigated into this issue with the recently proposed multiphase buffer theory. We show that historically, there is a transition in the dominant drivers of aerosol acidity in this region. Under the ammonia-poor conditions before ∼2008, the acidity is governed by HSO /SO buffering and the water self-buffering effect. Under the ammonia-rich conditions after ∼2008, aerosol acidity is mainly buffered by NH /NH. Buffering from the organic acids is negligible in the investigated period. In addition, the observed decrease in ammonium-to-sulfate ratio is due to the increased importance of non-volatile cations, especially after ∼2014. We predict that until ∼2050, the aerosols will remain in the ammonia-buffered regime, and the nitrate will remain largely (>98%) in the gas phase in southeastern U.S.
酸度是决定大气中水相物理和化学过程的一个重要参数，并且对气溶胶的气候、生态和健康影响有着强烈影响。传统上，人们认为气溶胶酸度会随着大气酸性物质（如二氧化硫、氮氧化物等）的排放增加而升高，随着碱性物质（如氨、灰尘等）的排放增加而降低。然而，美国东南部长达十年的观测结果似乎与这一假设不符：尽管氨相对于二氧化硫的排放量增加了三倍多，但预测的气溶胶酸度却保持稳定，而且观测到的颗粒相铵与硫酸盐的比率甚至在下降。在此，我们运用最近提出的多相缓冲理论对这一问题进行了研究。我们发现，从历史上看，该地区气溶胶酸度的主要驱动因素存在转变。在2008年之前氨含量较低的条件下，酸度受硫酸氢根/硫酸缓冲和水的自缓冲效应控制。在2008年之后氨含量较高的条件下，气溶胶酸度主要由铵根/氨缓冲。在所研究的时期内，有机酸的缓冲作用可忽略不计。此外，观测到的铵与硫酸盐比率下降是由于非挥发性阳离子的重要性增加，尤其是在2014年之后。我们预测，到2050年左右，美国东南部的气溶胶将仍处于氨缓冲状态，并且硝酸盐将在很大程度上（>98%）保持在气相中。
