The second question is: How high up in the atmosphere do we find aerosols and how long is the lifespan of aerosols?
Aerosols can be found as high as 20 miles in the atmosphere.
And the higher they are in the atmosphere, the longer, the longer they can remain.
Aerosols which are near the Earth's surface stay in the atmosphere for a few days or maybe a week,
because they're often washed out of the atmosphere by rain clouds.
But if they can reach very high in the atmosphere -- for example, in a volcanic eruption -- then they can remain for, for years.