The bill mostly just addresses intent, but I have some speculations as to mechanism.

Back in 2023, there were some reports that suggested the reduction in sulfur content in the fuel used in marine shipping was reducing cloud formation over the Atlantic and indirectly causing a change in ocean temperatures. In brief, it's cheaper to use high-sulfur fuel oil, so that's what most ships do. Burning that fuel releases particulates which harm human health--and also can act as seeds for cloud formation. International shipping regulations have gone into place that require lower sulfur fuel oil, or to scrub out the pollutants from the exhaust. The result is fewer toxic pollutants in the air, but also reduced cloud formation along major shipping lanes.

Aviation has a similar issue. Jet exhausts release soot particles and water vapor, which together can seed clouds, thus forming contrails. This additional cloud formation certainly has some impact on climate and weather, just like natural cloud patterns do. It's possible to use cleaner aviation fuel with less soot that forms fewer clouds, but that is likely to be more expensive, certainly in the near term, and thus the market incentives push airlines in the direction of using the cheaper, dirtier fuel.

So there is a clear mechanism by which different types of aviation fuel may cause the formation of "chemtrails" (contrails). The open question that the Tennessee law calls forth is whether some entity might be taking advantage of that side effect in an attempt to change climate patterns. An airline convinced of the harm of global warming and committed to sustainability might adjust their flight routing based on climate modeling to try to encourage cloud formation in specific areas.

Of course, the latter is pure speculation, as by definition it would be occurring out of the public eye.

I would expect the net effect of the Tennessee law to be that airline routes passing over that state are nudged in the direction of using cleaner fuel. At this point, claims of reduced contrails over the state are purely anecdotal, to my knowledge.

Sources: