Acid Rain
Acids (Arrhenius definition)
Anything that releases H+ in solutions
(aside on H+, H3O+, etc)
pH
pH = -log10[H+]
The hard part: pH is a log scale
Why isn’t water (pure) pH 7.0
CO2 + H2O
H2CO3
pH ~ 5.6
H+ + HCO3-
Where does the acid rain come from
Ans: Oxides of S and N.
SO3, SO2, NO, NO2 ≡ SOx, NOx
Where does SOx, NOx come from?
SOx burning of coal
coal C135H96O9NS S present in all living things
Simplified chemistry
S + O2
SO2 H2O H2SO3
HO
2 SO2 + O2
2 SO3 2 H2SO4
Problem is regional, not global or local
Effects of Acid Rain
CaCO3 + 2 H+
Ca++ + CO2 (s) + H2O
Reduced Visibility
Summer haze in Eastern U.S.
(aerosol of H2SO4, (NH4)2SO4, (NH4)HSO4
visibility East 1 – 25 mi
West. mnts 50 – 75 mi
Effect on Human Health
Elderly, very ill, chronic respiratory disease
Damage to Lakes + Streams
Why no problems in Midwest?
ANC ≡ acid neutralizing power
(ability of lake to resist changes in pH)
CaCO3 + CO2 + H2O
CaHCO3
+
HCO3 + H
H2CO3
CO2 + H2O
Effect on fish
Al
thick mucous forms on gills, fish suffocates
Control
Recovery strategy
“Lime” lakes, add CaCO3, Ca(OH)2
Coal switching
Low S coal
2 x cost, due to shipping problems
job loss in Appalachia
Natural Gas
no SOx, less NOx
Scrubbing
2 SO2 + O2 + 2 CaCO3
2 CaSO 4 + 2 CO2
Delayed effect of acid rain
Other problem: metal release
40% reduction in SO 2
50% reduction in SO 2
70% reduction in SO 2
$1 – 2 x 109 (8% increase in electricity
cost)
9
$2 – 4 x 10
$5 – 6 x 109