Your input is much appreciated; most of all by Tank, I think, because he / she may not be able to find a quiet stream in a wooded area in the city.
Seeing that you are involved in 'cellular engineering' I can understand your requirement for scientific proof. At least, however, we can agree that 'chi' does have an "effect" at the cellular level; whether it "works" at the cellular level or not can be left to another day for scientific consideration.
For the moment, how this 'effect' will work itself out in the long term practice of chi gung in a polluted environment is, I suppose at best, left unanswered. I for one will err on the side of caution; opening or closing of research grants notwithstanding.
Please do not take this in the wrong way (as we all know scientific methods as we understand them today, just like chi gung, have their own limitations) but I suppose Tank and everybody else may have to wait a while for the proof you require; unless of course some other member on the Forum have something to offer.
There is one cogent example from the tobacco industry which is illustrative of the issue at hand. For many decades this industry has demanded scientific proof from objectors that cigarette smoking has a direct causative link to lung cancer, while maintaining, understandably, that there was no scientific proof as such.
On the 'purification & distillation' point you brought up; well, these were ideas formulated in the days when pollution levels were not as there are today. My view is, there is only so much the body, even through chi gung practice, can do. There is always an 'overloading' point beyond which something has to give. Why give the body more stress than necessary? unless of course it is impossible to find a quiet stream in a wooded area; in which case one has to take a chance, I suppose.