Purpose of Review

The study of organic aerosol hygroscopic growth and cloud droplet activation is crucial for accurately quantifying their climate and environmental impacts. However, the physical mechanisms behind organic aerosol hygroscopicity variations are not well understood. In this review, we summarized laboratory and field measurements of the organic aerosol hygroscopicity parameter κ_OA, discussed the physical understanding of why κ_OA was generally positively correlated with organic aerosol oxidation level, summarized proposed κ_OA parameterization schemes, and examined possible explanations for the marked differences among these parameterization schemes.

Recent Findings

Recent findings challenged the general cognition that cloud condensation nuclei (CCN) activity of secondary organic aerosol depended largely on solubility, showing it to be mainly controlled by molecular weight, yet the universality of this finding needs to be further examined. It was found that carbon chain length and functional groups had significant impacts on κ_OA and additional parameters other than O/C ratio need to be included when parameterizing κ_OA of multifunctional compounds, which is typically the case for ambient atmospheric aerosols. Additionally, laboratory results of secondary organic aerosol suggest that κ_OA might be highly RH-dependent under sub-saturated conditions, especially for biogenic secondary organic aerosols.

Summary

This review summarized laboratory and field measurements of atmospheric organic aerosol hygroscopicity parameter κ_OA and its parameterization schemes. The results demonstrate that representing κ_OA with a single oxidation level parameter still bears large uncertainty, and physical mechanisms associated with hygroscopic growth and cloud activation processes of organic aerosol still remain unresolved and need further investigation.

中文翻译：

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大气有机气溶胶吸湿性及其基于氧化水平的参数化的室内研究与实测研究综述

审查目的

对有机气溶胶吸湿性生长和云滴活化的研究对于准确量化其对气候和环境的影响至关重要。然而，有机气溶胶吸湿性变化背后的物理机制还没有被很好地理解。在这次审查中，我们总结了有机气溶胶吸湿性参数的实验室和现场测量κ _OA，讨论了为什么物理理解κ _OA普遍肯定与有机气溶胶氧化水平相关，总结提出κ _OA参数化方案，并检查可能的解释这些参数化方案之间存在明显差异。

最近的发现

最近的发现挑战了普遍的认识，即次级有机气溶胶的云凝结核（CCN）活性很大程度上取决于溶解度，表明其主要受分子量控制，但是这一发现的普遍性需要进一步研究。据发现，碳链长度和官能团对显著影响κ _OA和比O / C比需要其他额外的参数参数化时，被包括κ _OA多官能化合物的，其通常用于环境大气气溶胶的情况。此外，二次有机气溶胶的实验室结果表明，κ _OA 在亚饱和条件下可能是高度依赖RH的，特别是对于生物成因的二级有机气溶胶。

概要

本文综述了大气有机气溶胶吸湿性参数的实验室和现场测量κ _OA和它的参数化方案。结果表明，占κ _OA与单个氧化水平参数仍然具有很大的不确定性，以及与有机气溶胶的吸湿性生长和云活化过程相关联的物理机制仍未得到解决，需要进一步调查。