Due to the air-tightness of a vessel

in atmospheric pressure dielectric barrier discharges（DBD） experiments or relevant application scenarios

the presence of air impurities is always unavoidable. We established a one-dimensional helium-air DBD ?uid model for the chemical description of the atmospheric pressure helium DBD-dry air including 26 species and 154 reactions to further study the main ionization processes and excited-state species evolutionary processes.The level of dry air was varied range from 1～200×10

–6

. The simulation results show that the electron impact ionization and Penning ioniza

tion constitute the most important reactions for electron production during breakdown

and oxygen molecules are more prone to Penning ionization by helium metastable atoms than nitrogen molecules. Additional important reactions are the associative ionization and stepwise ionization of excited-state species. However

results reveal that the influence of the electron detachment reaction is negligible on the discharge development because of the lower anion concentration. As the concentration of air impurities increases in the mixture

O

2

（a） becomes the dominant excited species owing to the lower reaction threshold

whereas

N

2

（C） always keeps the lowest concentration owing to the higher reaction threshold. The concentrations of He

*

and He2

*

related to Penning reactions are initially increased and then decreased during the increase in air concentration

and the difference is that the He2

*

content declines faster than the He

*

content.