1. 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?

2. CHAPTER 13: ACID RAIN

3. NATURAL pH OF RAIN Equilibrium with “natural” CO 2 (280 ppmv) results in a rain pH of 5.7: This pH can be modified by natural acids (H 2 SO 4, HNO 3, RCOOH…) and bases (NH 3, CaCO 3 )  natural rain has a pH in range 5-7 “Acid rain” refers to rain with pH < 5  damage to ecosystems

4. ENVIRONMENTAL IMPACTS OF ACIDITY

5. PRECIPITATION PH OVER THE UNITED STATES: 1994

6. CHEMICAL COMPOSITION OF PRECIPITATION Electoneutrality condition for acid rain based on predominant ions: [H + ] + [NH 4 + ] +2[Ca 2+ ] = 2[SO 4 2- ] + [NO 3 - ]

7. PH MEASURED IN CLOUD AND FOG WATER Courtesy: Jeff Collett

8. GLOBAL SULFUR BUDGET [Chin et al., 1996] (flux terms in Tg S yr -1 ) Phytoplankton (CH 3 ) 2 S SO 2  1.3d DMS  1.0d OHNO 3 Volcanoes Combustion Smelters SO 4 2-  3.9d 22 10 64 OH cloud, H +, H 2 O 2 42 818 4 dep 27 dry 20 wet dep 6 dry 44 wet H 2 SO 4 (g)

9. SULFUR CHEMISTRY Gas phase oxidation: SO 2 + OH  …  H 2 SO 4 slow, lifetime of SO 2 ~weeks R16 very fast: Titrates either SO 2 or H 2 O 2 in a cloud Aside: dissociation of sulfuric acid: In cloud oxidation (focus here on H 2 O 2 oxidation at low pH): SO 2 (g)  SO 2. H 2 O(13) SO 2. H 2 O  HSO 3 - + H + (14) H 2 O 2 (g)  H 2 O 2 (aq)(15) HSO 3 - + H 2 O 2 (aq) + H +  SO 4 2- + 2H + + H 2 O (16) Remember equilibrium constants: etc…. Rate of aqueous phase sulfate formation therefore:

10. GLOBAL SULFUR EMISSION TO THE ATMOSPHERE Chin et al. [2000] 2001 estimates (Tg S yr -1 ): Industrial 57 Volcanoes 5 Ocean 15 Biomass burning 1

12. Efficient scavenging of both HNO 3 (g) and nitrate aerosol

13. Efficient scavenging of both NH 3 (g) and ammonium aerosol

14. BUT ECOSYSTEM ACIDIFICATION IS PARTLY A TITRATION PROBLEM FROM ACID INPUT OVER MANY YEARS Acid-neutralizing capacity (ANC) from CaCO 3 and other bases Acid flux F H+

15. AREAS (IN BLACK) WITH LOW ACID-NEUTRALIZING CAPACITY

16. ACID RAIN: US-CANADA ENVIRONMENTAL POLICY ISSUE OF 1970’s - 1980’s http://archives.cbc.ca/environment/pollution/topics/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)

17. 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 O 2 to deep water  hypoxia N inputs to the Chesapeake Bay have increased 7-fold over natural!  1987 agreement to reduce N inputs by 40% [Boesch et al., 2001] Watershed estimates of controllable N inputs to Chesapeake

18. 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/Aci d04.ppt

19. TRENDS IN U.S. EMISSIONS OF SO 2

20. AMMONIUM AND SULFATE TRENDS, 1985-2004 NH 4 + SO 4 2- Lehmann et al. [2007]

21. TREND IN FREQUENCY OF ACID RAIN (pH < 5) Lehmann et al. [2007] 1994-1996 2002-2004

22. CHANGE IN PRECIPITATION PH FROM 1994 TO 2008

23. DEPLETION OF BASE CATIONS FROM ACID RAIN (Hubbard Brook Experimental Forest, New Hampshire)

24. STILL A MAJOR CONCERN IN INDUSTRIALIZING NATIONS…