I have some experience of this. Positive ions are very nasty. In some countrys, Isreal notably, they wouldn't perform operations when the wind was from a certain direction (from the desert), because the overload of Pos Ions made for bad judgement. I lived in Switzerland for a long time. The foen is a wind that makes people crazy and aggresive and is full of PO's. In NY I had an apt and I enstalled a negative ion machine. It worked but created dirty rings around every corner or object hanging on the wall. Neon light and carpeting made from synthetics are bad in this respect. Lightening creates floods of negative (good IO's), as does running water, especially ocean waves, which is one reason people feel good at the beach. There is a lot of research on the subject but as to it's influence on audio, I suspect it has more to do with mood altering than anything else.