Nonequilibrium atmospheric plasmas (NeAPs) are employed since many years for uses such as ozone generation, surface activation, or dust precipitation. Today, they are more and more in the focus of researchers due to the growing number of emerging applications for example in the field of novel therapeutic treatments in plasma medicine, deposition of thin films or nanostructured materials, plasma catalysis processes, treatments of liquids in electrolysis, plasma agriculture or remediation of volatile organic compounds.

NeAPs can generate high densities of reactive and excited species at very low or moderate gas temperatures which can be utilized in many surface treatment processes on almost every type of substrates including vacuum‐sensitive substrates such as fabrics, wood, liquids, or living tissues.

As for other plasma technologies, the development of these technologies is supported by the progress of the simulation of these discharges and by the development of efficient plasma‐diagnostic techniques adapted to the highly‐collisional atmospheric‐pressure conditions often combined with small plasma size and limited access. Nowadays, as a result of the strong efforts developed to characterize the NeAPs discharges, spatially and temporally resolved measurements of electric fields, plasma density, or reactive species densities are available. The special issue on “Nonequilibrium atmospheric plasma diagnostics” aims to illustrate the state‐of‐the‐art knowledge related to this matter by presenting a limited set of these diagnostic methods applied to specific applications. These applications include the polymerization of large molecular precursors, the dissociation and excitation of O₂ and N₂ molecules, the gas cleaning, the initiation of water chemistry, the deposition of hydrophilic and hydrophobic coatings, and the fundamental studies on jets used in plasma medicine. The studied plasma sources are manifold as well: non‐self‐sustained glow discharges, coronas, dielectric barrier discharges including guided streamers, radiofrequency plasmas, or ns‐pulsed discharges.

The radical measurements with laser‐induced fluorescence or threshold ionization molecular beam mass spectrometry are discussed, next to Rayleigh scattering, mass spectrometry of stable plasma‐chemistry products, particle tracking for gas transport analysis, fast imaging or shadowgraphy. This Special Issue also demonstrates that both the classical and “simple” current‐voltage characterization providing the power absorbed in plasma and the optical emission spectroscopy technique (extended to the vacuum‐ultraviolet range or even absolutely calibrated) still provide valuable information mandatory to guide more advanced diagnostics. Of course, to get the necessary global picture of the studied process, the plasma characterization is, in many cases, completed by the characterization of the deposited or treated material by conventional techniques such as X‐ray photoelectron spectroscopy, water contact angle, Fourier‐transform infrared spectroscopy, and others.

We believe that our readers will enjoy as much as we did the reading of this Special Issue and that it will give them a good insight into the diagnostic of nonequilibrium atmospheric plasmas.

多年来一直使用非平衡大气等离子体（NeAP）来产生臭氧，表面活化或粉尘沉淀等用途。如今，由于越来越多的新兴应用（例如在等离子药物中的新型治疗方法，薄膜或纳米结构材料的沉积，等离子催化过程，电解中的液体处理领域），它们越来越受到研究人员的关注。 ，等离子农业或挥发性有机化合物的修复。

NeAP可以在非常低或中等的气体温度下产生高密度的反应性和激发态物种，可在几乎所有类型的基材（包括对织物，木材，液体或活体组织等真空敏感基材）的许多表面处理过程中使用。

与其他等离子体技术一样，这些放电的模拟进展以及有效的等离子体诊断技术的发展为这些技术的发展提供了支持，这些技术通常适用于高碰撞大气压条件，并且通常伴随着等离子体尺寸小和局限性访问。如今，由于为表征NeAP放电做出了巨大努力，因此可以在空间和时间上解析电场，等离子体密度或反应性物种密度的测量结果。关于“非平衡大气等离子体诊断”的特刊旨在通过介绍适用于特定应用的有限的这些诊断方法集，来说明与该问题相关的最新知识。这些应用包括大分子前体的聚合，₂和N ₂分子，气体清洁，水化学的启动，亲水和疏水涂层的沉积以及对血浆医学中使用的喷嘴的基础研究。所研究的等离子体源也是多种多样的：非自持辉光放电，电晕，介电势垒放电（包括引导流光），射频等离子体或ns脉冲放电。

讨论了用激光诱导荧光或阈值电离分子束质谱进行的自由基测量，其次是瑞利散射，稳定的等离子体化学产物的质谱分析，用于气体传输分析的粒子跟踪，快速成像或阴影成像。本期特刊还表明，经典的和“简单的”电流-电压表征均提供了在等离子体中吸收的功率，以及光发射光谱技术（扩展至真空-紫外线范围，甚至经过了绝对校准）仍然提供了有价值的信息，以指导更多应用。高级诊断。当然，为了获得所研究过程的必要全局图，在许多情况下，等离子体表征是

我们相信我们的读者会喜欢阅读本期特刊，并且会为他们提供非常规大气等离子体诊断的良好见解。