Anyways, unless I'm mistaken, it seems really sensitive to sunlight- as the temps start dropping as soon as I put it in the shade, but doesn't seems to stabilize around 70F.
My old school mercury thermometer mounted in my garden reads way way high when sunshine is directly hitting it, and only accurate when mounted in the shade. I think if you want to read true air temperature you have to have the sensors shaded from direct sunlight as that is influnced by both air temp and direct photon exposure?
As far as any real calibration difference from your breadboard version Vs your standalone version I would have to see how you are powering the circuit between the two versions. Arduino analog input accuracy is directly related to how accurate the +5vdc supply voltage is.