Treatment of non-ideality in the multiphase model SPACCIM-Part2: Impacts on the multiphase chemical processing in deliquesced aerosol particles
Treatment of non-ideality in the multiphase model SPACCIM-Part2: Impacts on the multiphase chemical processing in deliquesced aerosol particles
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DOI：
10.5194/acp-2019-819
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发表时间：
2019-10
影响因子：
6.3
通讯作者：
A. J. Rusumdar;A. Tilgner;R. Wolke;H. Herrmann
中科院分区：
文献类型：
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作者：
A. J. Rusumdar;A. Tilgner;R. Wolke;H. Herrmann
抽象的。对流层潮解颗粒的特征是浓缩的非理想溶液(气溶胶、液态水或ALW)，它可以影响正在发生的多相化学。然而，目前的复杂多相化学模型一般还没有充分考虑和研究这种非理想溶液效应。因此，本研究旨在探讨非理想性对浓水气溶胶多相化学过程的影响。用多相化学模型(SPACCIM-SpactMod)在不同的环境和微物理条件下对非理想溶液进行了模拟，以评估其对水相化学过程的影响。研究表明，在90%RH-潮解气溶胶条件下，无机离子的活度系数往往小于1，而大多数不带电荷的有机化合物的活度系数值在1左右甚至更高。由于这种行为，模型研究表明，非理想性的包含在很大程度上影响了过渡金属离子(TMI)、氧化剂和相关化学子系统(如有机化学)的多相化学过程。与理想情况相比，在非理想碱性条件下，Fe(II)的化学生成通量和氧化通量都显著降低了2.8倍。在非理想碱性条件下的还原Fe(II)处理，包括降低Fenton反应的化学通量(−70%)，导致HOX/HOY的处理减少。在潮解的气溶胶条件下。因此，在非云期间模拟了较高的多相H_2O_2浓度(增大了3.1倍)和较低的水相OH浓度(降低了≈4倍)。对于H_2O_2，比较化学反应通量表明，最重要的汇，与HSO_3−的反应，在非理想碱性条件下比理想情况下高出40%，从而导致更有效的硫酸盐生成。另一方面，在非理想情况下，OH自由基的化学通量比理想情况下低约50%，包括有机气溶胶组分的降解通量较低。因此，考虑非理想性会以特定于化合物的方式影响在潮解颗粒条件下的化学处理和有机化合物的浓度。例如，潮解颗粒条件下氧化预算的减少导致浓度水平的增加和降低，例如重要的C2/C3羧酸。对于草酸，本研究表明，与在环境高污染条件下观察到的相比，非理想处理能够更现实地预测高草酸浓度。此外，模拟表明，由于不同的形成和降解过程受到不同的影响，较低的湿度条件，即较浓的溶液，可能会促进水相气溶胶中草酸浓度水平的提高。
Abstract. Tropospheric deliquesced particles are characterised by concentrated non-ideal solutions (aerosol liquid water or ALW) that can affect the occurring multiphase chemistry. However, such non-ideal solution effects have generally not yet been considered in and investigated by current complex multiphase chemistry models in an adequate way. Therefore, the present study aims at accessing the impact of non-ideality on multiphase chemical processing in concentrated aqueous aerosols. Simulations with the multiphase chemistry model (SPACCIM-SpactMod) are performed in different environmental and microphysical conditions with and without a treatment of non-ideal solutions in order to assess its impact on aqueous-phase chemical processing. The present study shows that activity coefficients of inorganic ions are often below unity under 90 % RH-deliquesced aerosol conditions, and that most uncharged organic compounds exhibit activity coefficient values of around or even above unity. Due to this behaviour, model studies have revealed that the inclusion of non-ideality considerably affects the multiphase chemical processing of transition metal ions (TMIs), oxidants, and related chemical subsystems such as organic chemistry. In detail, both the chemical formation and oxidation fluxes of Fe(II) are substantially lowered by a factor of 2.8 in the non-ideal base case compared to the ideal case. The reduced Fe(II) processing in the non-ideal base case, including lowered chemical fluxes of the Fenton reaction (−70 %), leads to a reduced processing of HOx/HOy. under deliquesced aerosol conditions. Consequently, higher multiphase H2O2 concentrations (larger by a factor of 3.1) and lower aqueous-phase OH concentrations (lower by a factor of ≈ 4) are modelled during non-cloud periods. For H2O2, a comparison of the chemical reaction fluxes reveals that the most important sink, the reaction with HSO3−, contributes with a 40 % higher flux in the non-ideal base case than in the ideal case, leading to more efficient sulfate formation. On the other hand, the chemical fluxes of the OH radical are about 50 % lower in the non-ideal base case than in the ideal case, including lower degradation fluxes of organic aerosol components. Thus, considering non-ideality influences the chemical processing and the concentrations of organic compounds under deliquesced particle conditions in a compound-specific manner. For example, the reduced oxidation budget under deliquesced particle conditions leads to both increased and decreased concentration levels, e.g. of important C2/C3 carboxylic acids. For oxalic acid, the present study demonstrates that the non-ideality treatment enables more realistic predictions of high oxalate concentrations than observed under ambient highly polluted conditions. Furthermore, the simulations implicate that lower humidity conditions, i.e. more concentrated solutions, might promote higher oxalic acid concentration levels in aqueous aerosols due to differently affected formation and degradation processes.