Acid Deposition

process by which acid-forming pollutants are deposited on Earth’s surface by… – wet- rain, snow, fog – dry- smoke or dust particles impacts on environment include: – deforestation – increased acidity in lakes and oceans – uptake of toxic minerals by plants or sea life – corrosion of marble, limestone, metals, etc...

precipitation (mostly rain) is the most common form of deposition

rainwater has natural pH of 5.6 – reacts with CO 2 to form weak carbonic acid – oyster video (6:07) oyster video – CO 2 + H 2 O ⇔ H 2 CO 3

acid rain – pH < 5.6 – primarily formed from sulfur dioxide (SO 2 ) and nitrogen oxides (NO or NO 2 ) these oxides dissolve in the rain to make – strong nitric acid (HNO 3 ) and sulfuric acid (H 2 SO 4 )

Causes industrialization – increasing emissions of nitrogen and sulfur oxides – coal burning volcanic emissions and biological processes

Effects of acid rain on structures

limestone and marble contain the base calcium carbonate (CaCO 3 ) when exposed to acid rain, a neutralization reaction occurs and the building is gradually eroded makes CaSO 4 or Ca(NO 3 ) 2 that is more soluble in water than the calcium carbonate

most metals contain iron – iron reacting with sulfuric acid rain (H 2 SO 4 ) to make FeSO 4

Prevention Pre-combustion methods: techniques used on fuel before combustion can reduce 80-90% of sulfur before combustion even occurs

Post-combustion methods: techniques used on gases after combustion remove sulfur dioxide, nitrogen oxides, and heavy metals from the gasses before they are released into the air – EX: calcium oxide or lime will react with sulfur dioxide and remove it from the gasses CaO (s) + SO 2 (g) ⇌ CaSO 3