Acid Deposition

acid because of presence of dissolved carbon dioxide - forms weak acid carbonic acid

• solutions with a pH below 5.6 • contain additional acids

• oxides of sulfur and nitrogen • primary pollutants

secondary pollutant

all processes by which acidic components as precipitates or gases leave the atmosphere

• wet acid deposition • dry acid deposition

rain, snow, fog fall to ground as aqueous precipitates

gases fall to ground as dust and smoke and dissolve in water to form acids

either 1,2 or 1,2,3,4

• either 1,3 or 2 • THEN • either 4 or 5

erodes buildings and statues

• increases rate of rusting • removes oxide layer on metal surfaces like Al

• slows growth and injures plants through leaching • dry deposition blocks pores for gas exchange

acid rain causes important minerals (Mg2+, Ca2+, K+) held in soil to become soluble and wash away before they can be absorbed by plants

• lakes become too acid to support life • eutrophication occurs

• over-fertilization of bodies of water caused by nitrates in acid rain • results in algal blooms leading to oxygen depletion

• sulfate and nitrate particles irritate respiratory tract • increase risk of asthma, bronchitis and emphysema • irritate eyes

• processes that reduce or remove sulfur present in coal or oil before combustion • crush coal and wash with water: high density sulfide sinks to bottom and separates from clean coal • hydrodesulfurisation: catalytic process that removes sulfur from refined petroleum products by reacting it with hydrogen to form hydrogen sulfide, used to manufacture sulfuric acid

flue-gas desulfurization: wet slurry reacts with SO2 to form neutral calcium sulfate - used to make plasterboard

• catalytic converters in vehicles: hot gases mixed with air pass over a platinum catalyst which converts toxic emissions into harmless products (picture = equation) • lower temperature combustion: recirculating exhaust gases back into engine lowers temperature to reduce emissions • lower demand for fossil fuels

lime neutralises acid