A primary air pollutant is put directly into air by human activity. What is a secondary air pollutant

Acid Rain

Explanation:

Acid rain, which is made up of several acidic compounds, forms when sulfur dioxide and nitrogen dioxide react in the air with water, oxygen and other chemicals. On the ground, acid rain damages plants and trees and increases the acidity levels of soils and bodies of water, causing damage to ecosystems. Acid rain also causes decay to buildings and can irritate the eyes and airways.

clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.