Science Buddies: "Ask an Expert"

i am doing the project with the cut out milk cartons. i put the vaseline on them and hung 2 experiments outside and 2 projects inside. the vaseline on the two outside turned yellow. is this because of the locations, or because of the sunlight turning the vaseline yellow. the locations outside was a train yard with diesel engines, and a somewhat busy intersection. please let me know.

amy

Amy,

How humid is it where you live? It could also be that the ones outside dried out more than the ones inside and that this changed the color. Both of the hypotheses you state (sunlight changing the color and the smog/etc. from the locations you chose changing the color) are possible. Did the yellow color come from the particulate matter you observed? If not, I suspect it was either sunlight or drying out. If you have time, you may want to put some more outside in a 'clean' location so you can compare them to the others that were left outside at 'dirty' locations.

thanks for the reply
i will put another outside in a cleaner location. there were some particles in it, but not enough to change the colors. the vaseline was not dried out. i did check it every day during the experiment, and the yellow darkened each day and the vaseline is not dried out. this leads me to believe it is the sunlight. i will put more outside in a clean location and see what happens.