Trees Preventing car Window Fogging

Okay, when I park my boyfriends car under a tree, it is the ONLY car in the parking lot that does not have fogged up windows in the morning...WHY???? He will be soooo impressed if I figure out the answer
- Tara (age 37)
Youngstown OH 44511

We have to post this one even though we don't know the answer, just in case someone else does.

Here's a couple of ideas, neither one very likely to be adequate.

1. At night, cars cool off partly by thermal electromagnetic radiation. The tree is warmer than the (very cold) distant night sky, so exchanging radiation with it won't cool the car as much. A little warmer car is less likely to have condensation. This effect is real, but somehow I doubt it's big enough. You could test it with a thermometer in the car, checking the morning readings and making some comparisons.

2. In the day cars heat up due to direct solar radiation. Trees provide shade, reducing that heating. As we all know, this is a big effect. The problem is, I don't see how it leads to less fogging at night unless people are leaving sodas in the cars, so that the amount of water vapor goes up more in the hot, unshaded cars. Again, there are obvious ways to test this idea.

Mike W.

(published on 08/05/2013)