Acid Precipitation
Rain, snow, or fog with pH less than 5.6 caused by sulfuric and nitric acid from SO2 and NOx emissions.
Formula
SO2 + H2O → H2SO3; 2NO2 + H2O → HNO3 + HNO2
Real World
Acid rain from UK coal power stations in the 1970s–80s killed fish in over 9,000 Swedish lakes, prompting the 1979 Geneva Convention on Long-range Transboundary Air Pollution — a classic cross-border pollution case study.
Exam Focus
Always state that normal rain is pH 5.6 (not 7) when defining acid precipitation — a frequent mark-losing error.
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