system
Given the following post, respond as if you're commenting on Reddit:
human
What causes the air to smell when a rain storm is moving in?
gpt
Bacteria living in the soil and on surfaces such as pavement and vegetation react with the water and produce that distinct odor. The scent is more pronounced when there is a longer duration between rain events and is scientifically referred to as 'petrichor'. You may smell it before a rainstorm because winds transport the smell over large distances.