Direct Quantification of the Effect of Ammonium on Aerosol Droplet pH
Direct Quantification of the Effect of Ammonium on Aerosol Droplet pH
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DOI：
10.1021/acs.est.0c07394
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发表时间：
2021-01-05
影响因子：
11.4
通讯作者：
Vikesland, Peter J.
中科院分区：
文献类型：
--
作者：
Huang, Qishen;Wei, Haoran;Vikesland, Peter J.
铵是一种重要的大气成分，决定了许多环境过程。使用pH纳米探针和表面增强拉曼光谱（Sers）的铵离子浓度对10-50 μ m的气溶胶液滴pH值的影响进行了量化。通过将1 M硫酸铵（AS）、硝酸铵（AN）、硫酸钠（SS）或硝酸钠（SN）溶液与1 M磷酸盐缓冲液（PB）以不同体积比混合制备样品溶液。测定了不同浓度下纯PB、AS和AN液滴的稳定pH值。1 M PB液滴的中心pH值与11相似，但当PB被铵（AS-或AN-PB）系统地取代时，液滴内的中心pH值从约11降至5.5。在钠（SS-或SN-PB）液滴中没有观察到这种降低，并且在硫酸盐和硝酸盐之间没有观察到pH差异。在含铵液滴中，氨分配到气相中被评估为可忽略不计。进行拉曼硫酸盐峰（类似于980 cm（-1））强度测量和表面张力测量以研究离子分布的变化。含铵液滴和不含铵液滴之间的pH差异归因于铵存在下离子分布的改变。
Ammonium is an important atmospheric constituent that dictates many environmental processes. The impact of the ammonium ion concentration on 10-50 mu m aerosol droplet pH was quantified using pH nanoprobes and surface-enhanced Raman spectroscopy (SERS). Sample solutions were prepared by mixing 1 M ammonium sulfate (AS), ammonium nitrate (AN), sodium sulfate (SS), or sodium nitrate (SN) solutions with 1 M phosphate buffer (PB) at different volume ratios. Stable pH values were measured for pure PB, AS, and AN droplets at different concentrations. The centroid pH of 1 M PB droplets was similar to 11, but when PB was systematically replaced with ammonium (AS- or AN-PB), the centroid pH within the droplets decreased from approximate to 11 to 5.5. Such a decrease was not observed in sodium (SS- or SN-PB) droplets, and no pH differences were observed between sulfate and nitrate salts. Ammonia partitioning to the gas phase in ammonium-containing droplets was evaluated to be negligible. Raman sulfate peak (similar to 980 cm(-1)) intensity measurements and surface tension measurements were conducted to investigate changes in ion distribution. The pH difference between ammonium-containing droplets and ammonium-free droplets is attributed to the alteration of the ion distribution in the presence of ammonium.