The readings you get will be off by a bit because the sensor is not meant to measure "true outside, ambient temp.". It is positioned close to the ground (as others have mentioned) in order to measure the temperature just above the pavement. If it reads a temperature within a few degrees of freezing, the little snowflake symbol will light up on your dash to remind you that the pavement is cold enough to cause ice formation, even if the air is not. Just another Volvo safety feature for those of us in northern climes.

Koz.