If the result to the user (getting a machine that leaves them with clean air except 1 type of polutant at exactly the level that polutant would be without the m

If the result to the user (getting a machine that leaves them with clean air except 1 type of polutant at exactly the level that polutant would be without the machine), is it really different ethically based on whether the machine leaves that polutant or removes then replaces it? Seems kind of like saying (although this example is certainly less ethical to those of us who oppose murder and death penalties) that there's a difference ethically between killing someone by putting poison into their body vs. killing them by preventing food/water to go into their body. But as to achieving it, sure I wasn't proposing it as necessarily a good or feasible option - other the little bit of research I did when choosing which air purifier for my bedroom I don't know much about the technology. I was more just thinking about the ethical question if it were possible, since I can appreciate the argument against it but like I said, I personally would be completely happy for a research team to offer me the hypothetical machine.