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Personally I am with you on this one and don't need to run any experiments. I am conscious that I actually FEEL different on the days they are not spraying us. Like today for example! Back to perfect blue skies again thank goodness :)

Barometric pressure will affect mood and can even cause headaches and other maladies and that also determines how long the vapor trails will stick around for.
https://healthfully.com/effects-barometric-pressure-humans-5410462.html

Humans are very sensitive to barometric pressure and you are more self aware than most.

That makes sense. But no matter the content, surely there must be a negative side effect to filling up the skies with it?

It's hard to say if it is a negative effect or not but there are measurable effects on surface temperatures caused by jet exhaust. Without them the surface would be a few degrees warmer. So it goes.

There is actually an interesting dichotomy between diesel emissions and gasoline emissions. Diesel has lots of particulates in its exhaust, mostly carbon, so it blocks the sun and cools the Earth, gasoline emissions have little particulates and lots of CO2 so they warm the Earth. Right now they somewhat balance each other out.

I think it's more like a few tenths of a degree than a few degrees. I recall there was a study done after the attacks of September 11th when all planes were grounded. There was definitely a measurable effect.

During the three-day commercial flight hiatus, when the artificial clouds known as contrails all but disappeared, the variations in high and low temperatures increased by 1.1 degrees Celsius (2 degrees Fahrenheit) each day, said meteorological researchers.

http://www.cnn.com/2002/TECH/science/08/07/contrails.climate/index.html

So they didn't reduce the overall temperature by that much, they reduced the daily temperature variation by that much. Contrails like clouds (which they essentially are for the most part) both reduce daytime highs by blocking/reflecting sunlight but increase nighttime lows by trapping heat. That article didn't make clear which is affected more.