## 1 Introduction  
In the conventional plasma applications, high-temperature (several thousand degrees Celsius or higher) atmospheric plasma and low-pressure (1/10,000 atm) nonthermal plasma have been used for analysis [1] and semiconductor manufacturing [2]. Recently, the stable generation of low-temperature plasma at approximately 50-100 \({}^{\circ}\)C under atmospheric pressure has become possible. This has significantly expanded the range of plasma applications. Applications of plasma, such as in disinfection [3] and hemostasis [4], wound healing [5], analysis of surface-adhesive compounds [6], and mobile on-site analytical devices [7], are examples that take advantage of the characteristics of atmospheric pressure and low-temperature generation of plasma. A simple technique to improve the effectiveness of plasma treatment, such as surface treatment, involves increasing the energy input during plasma generation [8]. In atmospheric low-temperature plasmas, the gas temperature of the plasma is inevitably higher than room temperature (15-25 \({}^{\circ}\)C), because energy is supplied to the gas at room temperature through discharge to generate the plasma [9]. Therefore, for the treatment of plants and other particularly heat-sensitive processing targets, it is necessary to design a system that allows processing to be performed at a temperature that is close to room temperature. [PERSON] et al. generated helium plasmas cooled with liquid nitrogen, and showed that it is possible to generate plasmas from cryogenic temperature to room temperature [10]. In addition, [PERSON] et al. reported a method to generate plasma at an arbitrary temperature by heating helium gas that is cooled by liquid nitrogen using a heater [11]. Although there are advantages to controlling plasma at low or room temperature to expand the range of applications, low- or room-temperature plasmas are not ideal for achieving certain processing effects. [PERSON] et al. investigated the influence of the gas temperature of helium plasma with oxygen on the bactericidal effect of plasma, and reported that it was enhanced by increasing the gas temperature of the plasma [12].  
It has also been reported that the selection of the gas species in plasma is important for improving the treatment effect. Different plasma gas species produce different surface treatments and bactericidal effects, which affects the type and number of reactive species produced [13; 14; 15]. [PERSON] et al. reported the introduction of proteins into tobacco leaves via plasma treatment with various gas species, such as argon, nitrogen, oxygen, and carbon dioxide. In this process, liquid nitrogen is used to cool the gas temperature of the plasma, to avoid thermal damage to the plant [16]. Thus, the gas species and temperature of the plasma have a significant influence on the plasma treatment effect. Therefore, if the gas species and temperature of the plasma can be arbitrarily controlled, it is expected that the range of applications will expand, and the conditions of plasma treatment can be optimized to maximize the effect.  
We have developed a multi-gas temperature-controllable plasma jet that can generate stable plasma with various gas species and control the gas temperature of the plasma. In this system, the plasmas can be generated with argon, helium, nitrogen, oxygen, carbon dioxide, or a mixture of these gases, and the gas temperature can be controlled in the range of 30-90 \({}^{\circ}\)C. In this study, the liquid was treated with plasma, and the reactive species generated by each plasma gas species were evaluated. In addition, the effects of plasma gas species and temperature on the bactericidal effects of carbon dioxide and nitrogen plasmas were evaluated.