Absorption and mainly emission spectrometry have been used to identify active species generated by a microwave induced surfatron plasma jet launched in open air and using argon flowing gas.The argon flow rate is kept constant at 1 L/min and
the microwave power is 40 W. We determined the ozone and atomic oxygen concentrations, ultraviolet C (UVC) irradiance, gas temperature, plasma electron density and excitation temperature. Most of these diagnostics are spatially resolved along
the plasma jet axis. Assessment of the biocide efficiency of the present low temperature plasma will be shown in the case of standard Gram-negative bacteria (Escherichia coli) and the main germicidal source of the jet is identified. A specific emphasis has been done for human health hazard assessment since simple solutions are reminded to respect safety standards for exposures to ozone and microwave leakage. These solutions should be adopted by users of microwave induced plasma in open air conditions because, according to the literature, this is not often the case.