###### Abstract  
Dry argon (Ar) discharge and wet oxygen/argon (O\({}_{2}\)/Ar) admixture discharge for alternating current atmospheric pressure plasma jets (APPJs) were studied for Ar discharges with flow rates ranging from 0.2 to 4 lsm and for O\({}_{2}\)/Ar discharges with different O\({}_{2}\) ratios and flow rates ranging from 2.5 to 15 mslm. The voltage-current waveform signals of APPJ discharge, gas flow rate, photo-imaging of the plasma jet length and width, discharge plasma power, axial temperature distribution, optical emission spectra, and irradiance were investigated. Different behavior for varying oxygen content in the admixture discharge was observed. The temperature recognizably decreased, axially, far away from the nozzle of the jet as the flow rate of dry argon decreased. Similar behavior was observed for wet argon with a lower temperature than for dry argon. The optical emission spectra and the dose rate of irradiance of a plasma jet discharge were investigated as a function of plasma jet length, for dry and wet Ar discharges, to determine the data compatible with the International Commission on Non-Ionizing Radiation Protection (ICNIRP) data for irradiance exposure limits of the skin, which are suitable for the disinfection of microbes on the skin without harmful effects, equivalent to 30 l/mm\({}^{2}\).  
atmospheric pressure plasma jet; oxygen/argon admixture; electrical and optical properties; emission intensity; dose of irradiance  
Received: 10 May 2021  
Accepted: 12 July 2021  
Low-temperature gas plasma applications dealing with the protocols of killing microorganisms have opened new fields in biotechnology applications. Recently, glow discharge plasma at atmospheric pressure has attracted significant attention, leading to many evaluations of the disinfection of bacteria by air plasmas at atmospheric pressure such as medical, environmental, and industrial evaluations [6].  
The configurations, characteristics, and applications of a cold plasma jet emerging by APPJ have attracted much attention: (i) configurations [7,8], such as electrode design, gas type, emerging plasma frequency, and flow rate; (ii) characteristics of the jet [9,10], such as length, width, temperature, emission spectra, irradiance, direct and indirect exposure, consumed energy, and consumed power; (iii) applications [11,12], such as the inactivation of microbes (water purification, sterilization, and wound healing), coating and etching (polymeric surface modification and synthesis of nanostructures), and medical applications (teeth bleaching, skin treatments, and cancer treatment).  
Moreover, there are important factors that affect the APPJ performance, such as tube dimensions and powering characteristics: (i) tube dimensions include material, shape, length, and the outer and inner diameter of the tube [13]; (ii) powering characteristics include power source, applied voltage, and frequency [14].  
Many publications have discussed the various applications of APPJs, such as the effect of the antimicrobial agent ratio on _Escherichia coli_ and its application in fresh-cut cucumbers by studying the survival curve shapes of different microbes, using the effects of different impact parameters on the characteristics of the plume emerging from the APPJ [15, 16, 17].  
The present work represents the characteristics of the cold plasma plume emerging from the APPJ under an alternating current (AC); these characteristics were studied by measuring the optical and electrical properties of the APPJ. These properties included the discharge voltage and current, output plasma power, axial distribution of temperature, flow rate, jet length, jet width, emission intensity of the plume, emission spectra, and the amount of energy emitted at each wavelength per unit area from the plasma jet using different gases, such as pure argon and an admixture of oxygen and argon at different ratios.