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Hygroscopic behavior and chemical composition evolution of internally mixed aerosols composed of oxalic acid and ammonium sulfate

机译：由草酸和硫酸铵组成的内部混合气溶胶的吸湿性和化学成分演化

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摘要

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.
机译：尽管气溶胶颗粒的水吸收在大气环境中起着重要作用，但组分对化学成分和颗粒的吸湿性之间的相互作用的影响仍然没有很好的限制。通过使用共焦拉曼光谱研究，由硫酸铵（AS）和由硫酸铵（AS）和OA组成的草酸（OA）和混合颗粒的混合颗粒进行研究。结果发现，OA液滴首先结晶以在71％相对湿度（RH）下形成OA二水合物，并进一步失去结晶水，在脱水过程中将结晶水转化为约5％RH的无水OA。迄今为止的潮解点为80.1 +/- 1.5％RH和44.3 +/- 2.5％RH。用于混合OA /作为液滴的观察到的兴华相对湿度（ERH）分别为1：3,1：1和3：1的液滴分别为34.4 +/- 2.0,44.3 +/- 2.0,44.4 +/- 3.0％RH ，表示升高的OA内容似乎有利于在更高的RH下结晶混合系统。然而，在混合OA /作为具有1：3和1：1的颗粒中的潮解相对湿度（DRH）分别观察到81.1 +/- 1.5和77 +/- 1.0％RH。混合OA /作为液滴的拉曼光谱表示从OA之间的相互作用和在脱水过程中的时间等级的脱水过程中的相互作用中形成氢氧化铵（NH 4 HC 2 O 4）和硫酸铵（NH4HSO4）的形成，其数量分别为随后影响随后的时间等级内部混合颗粒与不同OIR的潮解性行为。混合的OA /作为具有3：1的OIR的颗粒表现出由于大量的变化而在RH的RH范围内表现出潮解的过渡。 NH4 / 2SO4进入NH4HC2O4，具有高DRH。尽管混合OA /作为液滴的吸湿生长与在脱水过程中的高压下的AS或OA的差异相当，但潮解后混合颗粒的拉曼生长因子基本上低于兴坏过程中的混合OA /作为液滴的生长因子通过升高的OA内容进一步降低。在高压下脱水和水合过程之间的混合OA /作为颗粒的拉曼生长因子的差异可归因于NH 4 HC2O4和残留OA的显着形成，其在高温下保持着固体，从而导致混合颗粒的吸水性较少。这些发现改善了对气溶胶颗粒的化学和物理性质的二羧酸和无机盐之间的反应作用的理解，并且可能对大气化学具有重要意义。

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  • 来源
    《Atmospheric chemistry and physics》 |2017年第20期|共16页
  • 作者

    Wang Xiaowei; Jing Bo; Tan Fang; Ma Jiabi; Zhang Yunhong; Ge Maofa;

  • 作者单位

    Beijing Inst Technol Inst Chem Phys Sch Chem &

    Chem Engn Beijing 100081 Peoples R China;

    Chinese Acad Sci State Key Lab Struct Chem Unstable &

    Stable Speci CAS Res Educ Ctr Excellence Mol Sci BNLMS Inst Chem Beijing 100190 Peoples R China;

    Chinese Acad Sci State Key Lab Struct Chem Unstable &

    Stable Speci CAS Res Educ Ctr Excellence Mol Sci BNLMS Inst Chem Beijing 100190 Peoples R China;

    Beijing Inst Technol Inst Chem Phys Sch Chem &

    Chem Engn Beijing 100081 Peoples R China;

    Beijing Inst Technol Inst Chem Phys Sch Chem &

    Chem Engn Beijing 100081 Peoples R China;

    Chinese Acad Sci State Key Lab Struct Chem Unstable &

    Stable Speci CAS Res Educ Ctr Excellence Mol Sci BNLMS Inst Chem Beijing 100190 Peoples R China;

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  • 正文语种 eng
  • 中图分类 大气科学（气象学）;
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