Final answer:
Particulates commonly enter a reservoir from the air through atmospheric deposition, where particulate matter such as dust, soot, and other small particles, settle on water surfaces after being transported by wind.
Step-by-step explanation:
A common way particulates enter a reservoir from the air is through the process of atmospheric deposition. This occurs when particulate matter, which includes small particles such as dust, dirt, soot, viral particles, and bacteria, is carried over long distances by the wind and eventually settles on the surface of water bodies. This process can be enhanced in situations where burning of fossil fuels or wildfires release large quantities of primary pollutants into the air.