Nitrogen pollution | See Algal blooms. |  Fertlizer. | Haber-Bosch. | Nitrous oxide.

This comes in two forms: nitric oxides (NOx), mainly from combustion engines, and ammonia, mostly from fertlizer and animal waste. These lead to smog, algae blooms and other problems (‘Nitro dissidents’, The Economist 26th Oct 2019, p25).