The author deals with a new scientific direction in the physics of low-temperature plasma - development of physical fundamentals of cooling gas discharge plasma in humid air and long-lived plasma retention. The fundamental and applied results of investigations are presented. These were obtained recently with direct participation of the author and are published for the first time. Investigations of ionisation of humid air revealed previously unknown relationships of plasma cooling and variation of plasma properties as a result of regulation of the temperature of charged and neutral particles thus enabling the control of the rate of plasma recombination, weakening the intensity of the current neutralisation of a high-current electron beam and increasing the efficiency of the propagation of laser and electromagnetic radiation of the microwave range along a path containing water vapours.