Why positive ion decreases even with no recombination?

Hello I faced a problem and i have no idea why this happens

I'm simulating a air discharge(N2, O2, H2O) in a pulse applied voltage

this is global model (0 dimension)

I'm simulating in a step wise manner

This is problem in a time sequence

1. i noticed that electron decays even in a only ionizaiton reactions is enabled

2. In theory guide, electron is calculated by summation of other ion's charge

3. So after precise investigation, i noticed that positive ions decays right after the pulse discharge

4. why this happen? I disabled all the recombination and attatchment ( my expectation is ion density remains constant after ionization, pulse)

5. In 'equation view', there are no sink term in positive ions

6. Anyone can help me?