# Why fog and water have such a good relationship

Today in the morning, I was in the bus and when the bus was on a flyover (which was built on a river) I saw an interesting thing.

There was a lot of fog there, so much that it was impossible to see the river. when the bus came down I saw that fog wasn't much on the road (at least, things were visible there).

This observation popped a thought in my mind, Does water(water resources) attract fog ?? If this is true then what is the physical phenomena working behind it??

I thought that it is accidental and asked my physics teacher that is it possible?? His answer was ABSOLUTELY. But his explaination went over my head. I tried to get the answer on wikipedia and some other websites but all I found was definition and types of fog. So I m here.

Thanks for any help.

• Have you done any internet research to find an answer? PSE is not a substitute for doing your own research. ... If you don't understand your teacher's explanation, why not ask him to explain it more simply? Nov 6 '16 at 15:25
• @sammygerbil, I went on wiki and some other websites, but all i found was definition and types of fog Nov 6 '16 at 15:30
• So you have read en.wikipedia.org/wiki/Fog#Types. Advection and evaporation fogs are both formed over water. Nov 7 '16 at 1:34
• @sammygerbil the entire text of question is about the research the OP has already done. It's a good question. Nov 9 '16 at 4:10
• @Nathaniel : The only research which the OP mentions is in the last paragraph. He does not ask his teacher to explain his answer, and the very website he claims to have read contains an answer. The question itself is good, but the lack of prior research is not. Nov 9 '16 at 17:26

Water holds heat longer than the ground around it, due to the fact that water  possesses a higher heat capacity than most land surfaces. Water's high heat capacity results from the relatively large amount of heat energy needed to break it's hydrogen bonds.

When cold air moves over warmer water, some of the relatively warmer water evaporates (water vapor) into the lower air layers immediately above the water surface. This now warmer air rises, mixes with the cooler air, which in turn creates condensation, and if it's dense enough, we call it fog.

Or the water surface may be colder (from up river or last night) than the road surface (warming in the sun) and cause water vapour in the air to condense into fog. Thanks to KalleMP for pointing this out.

• Or the water surface may be colder (from up river or last night) than the road surface (warming in the sun) and cause water vapour in the air to condense into fog. Nov 6 '16 at 21:49

First you must understand why condensation (in your case, in the form of fog) occurs at all. Fog is nothing but tiny $\textit{liquid}$ water droplets (usually less than 10 micron) that have condensed on to dust particles that are present in air. When water is present in vapor form in the air, it has a partial pressure associated with it. For any given partial pressure, there is associated a temperature known as saturation temperature, below which water cannot exist in the form of vapor alone, but has to condense on to any available surface. Now higher the water vapor concentration, which in its turn implies higher water vapor pressure, higher is the corresponding saturation temperature.

While the air temperature on both the road and the lake may be the same, water vapor concentration (and hence its partial pressure) is likely to be greater in the vicinity of a water surface such as over a lake than on the road, especially in conditions when there is negligible wind. If water vapor pressure in air above the lake is high enough that the corresponding saturation temperature is higher than air temperature, then you will see fog only there and not anywhere else. This is a possible explanation for what you observed.

A nice book I would recommend for you to read is $\textit{Clouds in a glass of beer}$ by Craig F. Bohren.

• Nice and technical explanation. Nov 8 '16 at 1:02