如果你闻到,你吸入气体,颗粒,或两者的结合。他们通常不会建立在大气中,因为三个原因:运输/稀释(你提到),* *化学* *,* *沉积* *。是的有充足的新鲜空气,但就像你说的,在亿万年间会有很多积累有气味的化合物如果不是地方。虽然,臭空气被困在地上有时停滞期间的事件,造成温度反演近地表防止混合与高空。大气化学通常涉及羟基自由基(OH)。快速化学气体转换往往取决于哦,就是骑自行车和补充由于大气中大量的氧气和水蒸气。许多气体污染物会通过一系列的化学反应,哦,其他化学物质和/或阳光。然后转化为简单的化学品,我们并不真正的气味。大多数污染物化学转换迅速(如小时、天)但有些污染物需要数年才能转换(如甲烷),所以总有大量的甲烷在大气中。我们不闻,因为浓度低于我们的鼻子/大脑可以检测。 Deposition of air pollutants is dominated by precipitation, whereby rain can scavenge particles and chemically react with gases. The rain deposits the pollutants (usually in a modified form) onto the surface of the Earth. Dry deposition also occurs, especially with "sticky" compounds like ammonia. However, dry deposition is not nearly as efficient as wet deposition. Though, if particles are large enough, they will settle out of the atmosphere relatively quickly and deposit on the surface. I suggest you read up a little on the topic [here][1] to get you more familiar with the different factors that affect air pollutants. [1]: https://en.wikipedia.org/wiki/Air_pollution