Ok, let me take two here....

I started thinking about atmospheric pressure, and since I'm used to thinking about gas laws regading closed systems, find myself a little confused. I know 760 mm Hg is standard atmospheric pressure, but pressure, temperature, and number density (encompasses both molecules and volume) are all related by the ideal gas law. Although pressure, temperature and number of molecules decreases with altitude in the troposphere (and pressure, and number of molecules in the stratosphere), what happens at the surface when the temperature changes. I would think a higher temperature would actually increase both the number density and pressure due to faster molecular motion (which will collide with the surface more frequently, exerting more pressure) and due to a higher concentration of gas molecules becase of increased water vapor concentrations from evaporation (as temperature increases vapor pressure increases). But, then again, more evaporation means more condensation, etc., so maybe the water vapor concentration is not increasing, really... but, the molecular motion argument should still stand. However, pressure can also be defined as the weight of the air above, and this should be constant, meaning that surface atmospheric pressure does not change much...

So, how related is atmospheric pressure and temperature? Is the number density constant, so you'd just use the ideal gas law to determine the pressure at a different temperature? Or, does the number density increase because of more evaporation? or, better yet decrease because of expansion (as T increases, V increases), which may keep pressure constant?

Boy, I'll stick to my balloon scenarios in class!