It must be because the power plants produce so much pollution, it overwhelms everything else. I just tried it with recycling centres, and trees had a noticeable effect on air pollution. Large parks are even better if you can afford them. Although trees helped to contain pollution from the recycling centre, they appeared to be near their limit, so it's no surprise that they seemed to have no effect on a coal power plant, which I believe produces a hundred times more pollution than a recycling centre.

I think that there's only one building that can contain pollution from a coal power plant, and it requires a cheat code.

Ah that is interesting. I didn't think of trying it with recycling centers. So it indeed seems like power plant pollution is simply overpowering for trees. Parks too as it turns out. I didn't post the screenshot of it, but the last thing I tried was to replace as many of those trees in my experiment with large and small parks, and it still didn't show a noticeable difference.

Oh well, solar power plants all the way!

Question on Power Plants and selling power. The game tries to break you by forcing you to build or to cancel the deal and loose the Simoleons. Each time you near your upper limit, the game wants to renegotiate the power deal. The $ help build the City a bit faster. But too many power plants can become a real problem.

My plan is: build the power plant to satisfy the first couple demands. After that, cancel the deal and take a couple power plants "off line" by removing the power lines. Your neighboring town seems to negotiate to try to force you to your upper limit. With the plants off line, that upper limit should be a lot less. Once the new deal is in place, build the transmissions lines back. Deal in place and I don't have to build the new plant and go broke.

Trouble is: How far from other plants and transmission lines would the surplus power have to be in order to "take off line." In my present game, the plants are one or two squares apart. They operate as a single unit.

Thanks

PS
Doesn't work. The computer calculates total generating power. Not what is on line. The power deal just isn't worth it.