Ionic strength effects on the photochemical degradation of acetosyringone in atmospheric deliquescent aerosol particles
Ionic strength effects on the photochemical degradation of acetosyringone in atmospheric deliquescent aerosol particles
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DOI：
10.1016/j.atmosenv.2018.10.047
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发表时间：
2019-02
影响因子：
5
通讯作者：
Wentao Zhou;Majda Mekic;Jiangping Liu;Gwendal Loisel;Biao Jin;D. Vione;S. Gligorovski
中科院分区：
文献类型：
--
作者：
Wentao Zhou;Majda Mekic;Jiangping Liu;Gwendal Loisel;Biao Jin;D. Vione;S. Gligorovski
大量的实验室实验研究、现场活动和模拟结果强调了水相光化学反应在二次有机气溶胶（SOA）形成中的作用。然而，研究集中在高离子强度条件下的水相反应是稀缺的。在这里，我们研究了木质素衍生化合物乙酰丁香酮（AcS）在添加惰性盐（NaClO 4）后的光化学行为。离子强度的增加改变了AcS的酸性常数，增强了其去质子化作用。因此，由于电子跃迁n → π*（从λmax= 297 nm到λmax= 354 nm）和π → π*（从λ max = 214 nm到λmax= 247 nm）在高离子强度下的红移，AcS的UV-VIS吸收光谱经历修改。在固定的pH = 4时，代表中等酸性大气气溶胶潮解颗粒，AcS的伪一级速率常数（k1 st）从稀水相到具有有效离子强度Ieff的溶液增加了1.66倍。 0.46 M.然后，速率常数在升高的离子强度下遵循饱和趋势，直到Ieff = 3.1 M.在NaCl和Na 2SO 4的存在下，观察到的速率常数与离子强度的类似的饱和效应。差示吸收光谱法（DAS）的方法被应用于研究在长时间的光照射后的吸收光谱的变化。pH引起的照射AcS吸收光谱的非常微妙的变化是由于AcS光化学转化后形成的酸性化合物。
A number of laboratory experimental investigations, field campaigns, and modeling results have emphasized the role of aqueous-phase photochemical reactions in the formation of secondary organic aerosols (SOA). However, investigations focused on aqueous-phase reactions under high ionic-strength conditions are scarce. Here we study the photochemical behavior of a lignin-derived compound, acetosyringone (AcS), upon addition of an inert salt (NaClO4). The increase in the ionic strength modifies the acidic constant of AcS, enhancing its deprotonation. As a consequence, the UV-VIS absorption spectra of AcS undergo modifications due to red shifts at high ionic strength of the electronic transitions n → π* (from λmax= 297 nm to λmax= 354 nm) and π → π* (from λmax= 214 nm to λmax= 247 nm). At fixed pH = 4, representative of moderately acidic atmospheric aerosol deliquescent particles, the pseudo-first-order rate constants (k1st) of AcS increased by ∼6 times from a dilute aqueous phase to a solution with an effective ionic strength Ieff.= 0.46 M. The rate constant then followed a saturation trend at elevated ionic strength up to Ieff.= 3.1 M. A similar saturation effect of the observed rate constants with ionic strength was observed in presence of NaCl and Na2SO4. Differential absorption spectroscopy (DAS) methodology was applied to examine the changes in absorption spectra of AcS upon prolonged light irradiation. The very subtle pH-induced changes of the absorption spectra of irradiated AcS are due to the formation of acidic compounds emerged upon photochemical transformation of AcS.