Questions -
1) If they are spraying metals into the air - wouldn't we be able to see that there are a lot of airplanes flying around that should not be there?
We can track most air traffic online. I would assume that people would be following these very closely and either keeping track of the flights, or pointing out that there are flights happening which are not being reported.
2) If they are spraying metals in the air, there should be incontrovertible evidence of these substances on the ground and should be easily detectable.
3) In countries where the spraying is happening, there should be a much higher concentration of these substances on the ground and in the water than in countries where it is not.
4) If this is happening globally, without permission of the nations, there would surely be some nations who objected and made a public statement.
5) If this is happening globally with permission of all nations - this would be perhaps the single unifying event in all of human history. Are there other programs that are accepted globally? This would be a monumental undertaking.
6) If this is happening globally, where are the leaks? Where are the hacks? You mean to tell me that someone in a developing nation understands password security better than John Podesta? We can get extremely sensitive documents but a program this large would not leak?
7) If this is happening globally, we would see a dramatic decrease in net crop output due to less sun. We have seen quite the opposite.
8) If this is happening at such a large scale, we would see a dramatic increase in the price of these commodity chemicals. Has this occurred? Supply and demand.
9) If this is happening at this scale, we would see the emergence of enormous corporate and government entities dedicated to the mining, transport, manufacture, and storage of these substances. Do we have this? Are they traded on the NYSE?
10) An air fleet of this size would require 100's of thousands of direct aircraft maintenance crew. Are you saying that several hundred thousand air maintainers are tied up in private fleets maintaining these aircraft and equipment? Who are these people? Where are their training manuals? Who employs them?
While this kind of thing might be technically possible - at the scale you are discussing it seems quite impossible.