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可以假设大气(主要是氮)比水重(蒸汽)?

水和大气冷却能力降低。然而,大气密度冷沉而温暖,轻气氛上涨。可以假设大气(主要是氮)比水重(蒸汽)?

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是的,潮湿的空气密度较低,但温度和压力是在空气的密度更大的因素。温度和压力是推动上升气流和比watervapor风速和方向。(绝对湿度)[1],或者在空气中水蒸气的质量,是一个小的因素。[这][2]的更多细节。* *温度* * 5°的改变可以改变空气密度近2%。这意味着,撒哈拉沙漠(35°c)和北极(-25°),湿度和压力不变的情况下,北极的空气密度是24%左右。在当地,如果我们假设15°变化每天或每年25至35°变异,在本地的5% - -14%,误差,基于温度。* *压力* * /(阿伏伽德罗定律)[3],增加10%的压力,其他一切不变的情况下,对应于气体密度增加10%。10%的空气压力的变化是相当(除非你爬一个山高)。在本地,10%空气压力的变化是罕见的,除非你看记录。 Daily/Weekly highs and lows in barometric pressure might vary air density by 3%-7%, ballpark estimate. See some record high and low pressure [here][4]. **Water Vapor** Again, using Avogadro's law, if you add 1 water vapor molecule to the atmosphere, and maintain temperature and pressure, you need to push one other gas molecule out of the set volume, so per cubic meter, increasing humidity does displace some of the heavier gas molecules, so there is some lightening of the air, but the effect is quite small. Water-vapor has a molecular mass of 18. Our Oxygen-Nitrogen atmosphere has an average mass of about 29. But Water Vapor rarely takes up more than 1% of the atmosphere, perhaps 2% in hot climate, 3% in very hot, but that's 3% of the air with a 38% decrease in mass, resulting in a net change of less than 1% in the most extreme conditions. You'd be unlikely to see a variation of as much as 1% density by water vapor alone, outside of a very rare event, like a thunderstorm over a desert. There's other factors for wet air, such as the evaporation of water has a cooling effect, so as water evaporates, the local atmosphere cools, so mid day when sunlight driven or wind driven evaporation is at it's peak, it's not quite so neat and tidy as to say that evaporation makes the air lighter, cause the cooling effect of evaporation may actually make the air slightly more dense, not less dense. It's only less dense if you keep everything equal, but the cooling effect of evaporation doesn't keep everything equal. That said, however you look at it, water vapor is likely an order of magnitude less important for air-density than temperature and pressure. It's relevant enough to pay attention too if you want to study air-density carefully, but temperature and pressure are the two big factors. A possible exception to this is when there's fog. Fog contains tiny water droplets which are small enough to be suspended in air by wind, and those individual droplets are much denser than atmospheric water-vapor. foggy air, under the right conditions might be the most dense air, but in a sense, that shouldn't count, it's like counting sand in a sandstorm as part of the mass of air. ((Corrections welcome if I made any errors)). [1]: https://en.wikipedia.org/wiki/Humidity#Absolute_humidity [2]: https://en.wikipedia.org/wiki/Density_of_air#Density_of_air_variables [3]: https://en.wikipedia.org/wiki/Avogadro%27s_law [4]: https://www.wunderground.com/resources/pressure_records.asp

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