Question

how does air pollution leads to water pollution

Answer 1

nitrogen compound in air pollution are partly because of algal blooms and can also contribute to water body is becoming more acidic and 1 nitrogen oxide is releasing atmosphere they come back on the earth in the form of rain and this rain is known as acidic rain and cause water pollution

Answer 2

Pollution also comes from trash, chemical, fertilizers etc, sometimes water pollution is also in the air, when water vapour occupy some chemical gases it becomes more acidic, acidic rain will fall as rain which will lead to water pollution.
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Hope it helps!