## 2 Plasma and Aerosols: Opportunities, Economical and Societal Benefits  
All these recent advances should, in our opinion and as has already been documented in the literature [19; 20; 22], result in a strong effort and a specific interest in the development, optimization and applications of plasma in interaction with liquid droplets and aerosols in various fields of technology over the next decade. The topic of this paper is to summarize the opportunities for generating and delivering plasmas into aerosols and sprays, as a specific branch of plasma-liquid science and technology. The term \"plasma-aerosol\", where \"aerosol\" means a dynamic suspension of liquid droplets dispersed in a gas, encompasses a wide range of scenarios that can involve a range of options, from single microscopic droplets up to dense sprays and jets, while atmospheric pressure plasmas may vary from the low temperature and non-equilibrium family of devices to extremely hot plasmas. The plasma-aerosol configuration offers special beneficial advantages, not only in furthering the development of plasma-liquid applications, but also enabling greater scientific insights into what is an extremely complex problem involving potentially thousands of transient and non-equilibrium chemical reactions. Moreover, the incorporation of large surface-to-volume ratio media into cold plasma creates new opportunities, correlated to highly demanding societal and technological needs, in:  
* _Enhancing the transfer of activation energy from the plasma to the liquid._ Batch processes are often limited by the transport of species through the liquid surface. This limit is overcome in the plasma-aerosol configuration thanks to a large surface-to-volume ratio and the production of species in close proximity to the droplet surface. * _Controlling reactivity in the liquid._ The droplets can act as individual microreactors, enabling a range of conditions that cannot otherwise be achieved in batch processes. * _In-flight production and on-demand delivery of designed micro/nanomaterials_ associated with the generation of clusters and/or liquid evaporation. Aerosol droplets could be employed as micro-carriers, able to deliver particles and molecules in the discharge region opening, for example, for the use of low-volatility liquid compounds. * _Delivery of short-lived species._ Plasma-aerosol driven by high velocity sprays may represent a new and unique way to generate and deliver significant amounts of short-lived species (sub-second lifetime) together with solvated electrons away from the plasma itself on millisecond timescales. Dealing with economic benefits, in the synthesis of high value chemicals, drugs and nanomaterials, there is an increasing trend to move away from batch processing, which is expensive, difficult to control, and has an unwelcome environmental impact. Efficient green process research is looking to develop micro reaction technology. Plasma and aerosols offer many further advantages with regard to cross-contamination, throughput, chemical recovery and waste generation. In addition, the ability to generate high value chemicals, locally and on-demand, offers tremendous potential. This includes, for example, pristine or drug-coated nanoparticle generation and delivery to patients for nanomedicine applications (e.g., wound healing and cancer treatment) and size-controlled nanoparticles for volume catalytic processes. Alternatively, the encapsulation of biomolecules, drugs, and nanocarriers in liquid droplets seems to prevent possible plasma-induced damage during the deposition of bioactive, nanostructured and functional coatings, allowing the retention in the deposited coating of important chemical functionalities [23; 24; 25; 26]. On the side of energy saving, the valuable work of [PERSON] and [PERSON] [27] on energy yields for H\({}_{2}\)O\({}_{2}\) generation by plasma-water processes reported how the highest efficiency is achieved by adopting liquid droplets that sequester H\({}_{2}\)O\({}_{2}\) and hinder its decomposition by radicals in the gas phase.