Editing Acid rain (section)

==Definition==
"Acid rain" is rain with a pH less than 5.<ref>{{cite book |title=IUPAC GoldBook: Acid rain |chapter=Acid rain |date=2008 |publisher=International Union of Pure and Applied Chemistry (IUPAC) |location=Research Triangle Park, NC |doi=10.1351/goldbook.A00083 |chapter-url=https://goldbook.iupac.org/terms/view/A00083}}</ref> "Clean" or unpolluted rain has a pH greater than 5 but still less than pH = 7 owing to the acidity caused by carbon dioxide acid according to the following reactions:

:{{Chem2|H2O + CO2 <-> H2CO3 }}
:{{Chem2|H2O  + H2CO3 <-> HCO3− + H3O+}}

A variety of natural and human-made sources contribute to the acidity. For example [[nitric acid]] produced by [[electric discharge]] in the atmosphere such as [[lightning]].<ref name=":15">{{cite journal |last1=Likens |first1=Gene E. |last2=Keene |first2=William C. |last3=Miller |first3=John M. |last4=Galloway |first4=James N. |title=Chemistry of precipitation from a remote, terrestrial site in Australia |journal=Journal of Geophysical Research: Atmospheres |date=November 20, 1987 |volume=92 |issue=D11 |pages=13299–13314 |doi=10.1029/JD092iD11p13299 |bibcode=1987JGR....9213299L |url=https://zenodo.org/record/1231444 }}</ref> The usual anthropogenic sources are [[sulfur dioxide]] and [[nitrogen oxide]].  They react with water (as does carbon dioxide) to give solutions with pH < 5.<ref name=":1"/> Occasional pH readings in rain and fog water of well below 2.4 have been reported in industrialized areas.<ref name="NASA Glossary"/>