QUESTIONS

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QUESTIONS

1. Is the rate of reaction of S(IV) more likely to
   be slower than calculated for a cloud droplet or
   a rain droplet? Why?
2. If you wanted to determine whether a species
   would be a good oxidant in the aqueous phase what
   are the 3 things you would need to know?

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CHAPTER 13 ACID RAIN
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NATURAL pH OF RAIN

• Equilibrium with natural CO2 (280 ppmv)
  results in a rain pH of 5.7

This pH can be modified by natural acids (H2SO4,
HNO3, RCOOH) and bases (NH3, CaCO3) ? natural
rain has a pH in range 5-7
Acid rain refers to rain with pH lt 5 ? damage
to ecosystems
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ENVIRONMENTAL IMPACTS OF ACIDITY
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PRECIPITATION PH OVER THE UNITED STATES 1994
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CHEMICAL COMPOSITION OF PRECIPITATION
Electoneutrality condition for acid rain based on
predominant ions H NH4 2Ca2
2SO42- NO3-
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PH MEASURED IN CLOUD AND FOG WATER
Courtesy Jeff Collett
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GLOBAL SULFUR BUDGET Chin et al., 1996(flux
terms in Tg S yr-1)
SO42- t 3.9d
SO2 t 1.3d
cloud, H, H2O2
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OH
H2SO4(g)
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4
OH
NO3
(CH3)2S
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dep 6 dry 44 wet
DMS t 1.0d
10
dep 27 dry 20 wet
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Phytoplankton
Volcanoes
Combustion Smelters
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SULFUR CHEMISTRY
Aside dissociation of sulfuric acid
Gas phase oxidation SO2 OH ? ? H2SO4 slow,
lifetime of SO2 weeks
In cloud oxidation (focus here on H2O2 oxidation
at low pH) SO2(g) ? SO2.H2O (13) SO2.H2O ?
HSO3- H (14) H2O2(g) ? H2O2(aq) (15) HSO3
- H2O2(aq) H ? SO42- 2H H2O
(16) Remember equilibrium constants
etc. Rate of aqueous phase sulfate formation
therefore
R16 very fast Titrates either SO2 or H2O2 in a
cloud
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GLOBAL SULFUR EMISSION TO THE ATMOSPHERE
2001 estimates (Tg S yr-1) Industrial 57
Volcanoes 5 Ocean 15 Biomass burning
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Chin et al. 2000
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(No Transcript)
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Efficient scavenging of both HNO3(g) and nitrate
aerosol
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Efficient scavenging of both NH3(g) and ammonium
aerosol
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BUT ECOSYSTEM ACIDIFICATION IS PARTLY A TITRATION
PROBLEM FROM ACID INPUT OVER MANY YEARS
Acid flux FH
Acid-neutralizing capacity (ANC) from CaCO3 and
other bases
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AREAS (IN BLACK) WITH LOW ACID-NEUTRALIZING
CAPACITY
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ACID RAIN US-CANADA ENVIRONMENTAL POLICY ISSUE
OF 1970s - 1980s
http//archives.cbc.ca/environment/pollution/topic
s/584/
Dying lakes, dying crops A long awaited agreement
A policy debate that was ultimately addressed
with domestic legislation (Eastern Canada Acid
Rain Program in 1985 and US amendment to Clean
Air Act in 1991)
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EXCESS NITROGEN DEPOSITION CAN ALSO LEAD TO
EUTROPHICATION OF LAKES AND RIVERS
Excessive deposition of assimilable N ?
eutrophication ? accumulation of algae ?
suppression of supply of O2 to deep water ?
hypoxia
N inputs to the Chesapeake Bay have increased
7-fold over natural!
? 1987 agreement to reduce N inputs by 40
Watershed estimates of controllable N inputs to
Chesapeake
Boesch et al., 2001
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SOLUTIONS TO ACID DEPOSITION?
CHEMICAL Liming addition of calcium
carbonate. Works, but is expensive and only a
short term solution
BIOLOGICAL Long-term solution reduce
emissions and let lakes recover naturally
www.life.uiuc.edu/ib/349/lectures/Acid04.ppt
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TRENDS IN U.S. EMISSIONS OF SO2
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AMMONIUM AND SULFATE TRENDS, 1985-2004
NH4
SO42-
Lehmann et al. 2007
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TREND IN FREQUENCY OF ACID RAIN (pH lt 5)
1994-1996
2002-2004
Lehmann et al. 2007
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CHANGE IN PRECIPITATION PH FROM 1994 TO 2008
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DEPLETION OF BASE CATIONS FROM ACID RAIN(Hubbard
Brook Experimental Forest, New Hampshire)
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STILL A MAJOR CONCERN IN INDUSTRIALIZING NATIONS