The effect of electronegative additives on the conversion of toxic impurities in plasma of air mixtures was studied. Using the example of the conversion of trichloroethylene C2HCl3 in air under the influence of pulsed corona discharge of nanosecond duration, it was shown that the addition of carbon tetrachloride CCl4 to the mixture leads not only to a decrease in the discharge current, but also to an increase in energy efficiency of the conversion of C2HCl3. The analysis of processes in various areas of the corona discharge is carried out.