Hygroscopic behavior and chemical composition evolution of internally mixed aerosols composed of oxalic acid and ammonium sulfate
Hygroscopic behavior and chemical composition evolution of internally mixed aerosols composed of oxalic acid and ammonium sulfate
复制标题
草酸和硫酸铵内部混合气溶胶的吸湿行为和化学成分演化
DOI：
10.5194/acp-17-12797-2017
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发表时间：
2017
影响因子：
6.3
通讯作者：
Ge Maofa
中科院分区：
文献类型：
--
作者：
Wang Xiaowei;Jing Bo;Tan Fang;Ma Jiabi;Zhang Yunhong;Ge Maofa
抽象的。尽管大气环境中气溶胶粒子的吸水作用起着重要作用，但组分之间的相互作用对粒子的化学组成和吸湿性的影响仍然没有得到很好的限制。用共聚焦拉曼光谱研究了草酸(OA)及其与硫酸铵(AS)和不同有机无机摩尔比(OIRS)组成的混合粒子的吸湿性和相变。研究发现，在相对湿度为71 %(RH)的条件下，OA液滴首先结晶生成二水OA，然后在RH为5 %左右的脱水过程中，进一步失去结晶水转化为无水的OA。测得As的潮解点和风化点分别为80.1 ± 1.5 %和44.3 ± 2.5 %。OIR分别为1 ： 3、1 ： 1和3 ： 1的混合油滴的风化相对湿度(ERH)分别为34.4 ± 2.0、44.3 ± 2.5和64.4 ± 3.0 %，表明油酸含量的增加有利于混合体系在较高相对湿度下的结晶。然而，在OIR分别为1 ： 3和1 ： 1的混合OA / As颗粒中，As的潮解相对湿度分别为81.1 ±1.5和77 ± 1.0 %。混合的OA / As液滴的拉曼光谱表明，在数小时的时间尺度上，OA与气溶胶中的As相互作用生成草酸氢铵(NH4HC2O4)和硫酸氢铵(NH4HSO4)，这对不同OIR的内部混合颗粒随后的潮解行为有很大影响。在所研究的RH范围内，OIR为3 / 1的混合OA ： AS粒子没有发生潮解转变，这是因为(NH_4)_2SO_4转化为具有较高DRH的NH_4HC_2O_4。尽管在高相对湿度下，混合OA / As液滴的吸湿性与As或OA相当，但在风化过程中，混合颗粒经潮解后的拉曼生长因子显著低于混合OA / As液滴，并随着OA含量的增加而进一步降低。混合 / 的拉曼生长因子在高RH下的脱水和水化过程中的差异可以归因于在高RH下形成大量的NH4HC2O4和残留的OA，它们保持固体状态，从而导致混合颗粒的吸水率较低。这些发现促进了对二元酸和无机盐之间的反应在气溶胶粒子的化学和物理性质中的作用的理解，并可能对大气化学有重要的意义。
Abstract. Although water uptake of aerosol particles plays an important role in the atmospheric environment, the effects of interactions between components on chemical composition and hygroscopicity of particles are still not well constrained. The hygroscopic properties and phase transformation of oxalic acid (OA) and mixed particles composed of ammonium sulfate (AS) and OA with different organic to inorganic molar ratios (OIRs) have been investigated by using confocal Raman spectroscopy. It is found that OA droplets first crystallize to form OA dihydrate at 71 % relative humidity (RH), and further lose crystalline water to convert into anhydrous OA around 5 % RH during the dehydration process. The deliquescence and efflorescence point for AS is determined to be 80.1 ± 1.5 % RH and 44.3 ± 2.5 % RH, respectively. The observed efflorescence relative humidity (ERH) for mixed OA ∕ AS droplets with OIRs of 1 : 3, 1 : 1 and 3 : 1 is 34.4 ± 2.0, 44.3 ± 2.5 and 64.4 ± 3.0 % RH, respectively, indicating the elevated OA content appears to favor the crystallization of mixed systems at higher RH. However, the deliquescence relative humidity (DRH) of AS in mixed OA ∕ AS particles with OIRs of 1 : 3 and 1 : 1 is observed to occur at 81.1 ± 1.5 and 77 ± 1.0 % RH, respectively. The Raman spectra of mixed OA ∕ AS droplets indicate the formation of ammonium hydrogen oxalate (NH4HC2O4) and ammonium hydrogen sulfate (NH4HSO4) from interactions between OA and AS in aerosols during the dehydration process on the time scale of hours, which considerably influence the subsequent deliquescence behavior of internally mixed particles with different OIRs. The mixed OA ∕ AS particles with an OIR of 3 : 1 exhibit no deliquescence transition over the RH range studied due to the considerable transformation of (NH4)2SO4 into NH4HC2O4 with a high DRH. Although the hygroscopic growth of mixed OA ∕ AS droplets is comparable to that of AS or OA at high RH during the dehydration process, Raman growth factors of mixed particles after deliquescence are substantially lower than those of mixed OA ∕ AS droplets during the efflorescence process and further decrease with elevated OA content. The discrepancies for Raman growth factors of mixed OA ∕ AS particles between the dehydration and hydration process at high RH can be attributed to the significant formation of NH4HC2O4 and residual OA, which remain solid at high RH and thus result in less water uptake of mixed particles. These findings improve the understanding of the role of reactions between dicarboxylic acid and inorganic salt in the chemical and physical properties of aerosol particles, and might have important implications for atmospheric chemistry.