1 / 27

NATURAL pH OF RAIN

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 ) e natural rain has a pH in range 5-7. “Acid rain” refers to rain with pH < 5 e damage to ecosystems.

elmer
Download Presentation

NATURAL pH OF RAIN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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) e natural rain has a pH in range 5-7 “Acid rain” refers to rain with pH < 5 e damage to ecosystems

  2. PRECIPITATION PH OVER THE UNITED STATES

  3. CHEMICAL COMPOSITION OF PRECIPITATION Neutralization by NH3 is illusory because NH4+g NH3 + H+ in ecosystem

  4. LONG-TERM TREND IN US SO2 EMISSIONS

  5. Power plant emission trend: “NOx SIP Call” Long-term trend in US NOx emissions

  6. Sulfate wet deposition and aerosol concentrations, 1980-2010 Leibensperger et al. [2011]

  7. Ammonium wet deposition and aerosol concentrations, 1980-2010 Leibensperger et al. [2011]

  8. Nitrate wet deposition and aerosol concentrations, 1980-2010 Leibensperger et al. [2011]

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

  10. 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

  11. BIOGEOCHEMICAL CYCLING OF MERCURY ATMOSPHERE Hg (gas) combustion industry mining volcanoes erosion deposition re-emission SOIL OCEAN burial SEDIMENTS DEEP EARTH

  12. Electronic structure of mercury Mass number = 80: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 • Complete filling of subshells gives elemental Hg(0) stability, high volatility • Two stable oxidation states: Hg(0) and Hg(II)

  13. Orbital energies vs. atomic number Energetic arrangement of orbitals is such that mercury (Z=80) has all its subshells filled

  14. BIOGEOCHEMICAL CYCLING OF MERCURY ATMOSPHERE Hg (gas) combustion industry mining volcanoes erosion deposition re-emission SOIL OCEAN burial SEDIMENTS DEEP EARTH

  15. Global mercury deposition has roughly tripled since preindustrial times RISING MERCURY IN THE ENVIRONMENT Dietz et al. [2009[

  16. Tuna is the #1 contributor HUMAN EXPOSURE TO MERCURY IS MAINLY FROM FISH CONSUMPTION Mercury biomagnification factor State fish consumption advisories EPA reference dose (RfD) is 0.1 μg kg-1 d-1 (about 2 fish meals per week)

  17. MERCURY CYCLING INVOLVES CHEMICAL TRANSFORMATION elemental mercury VOLATILE mercuric compounds WATER-SOLUBLE ATMOSPHERE Hg(0) Hg(II) oxidation TRANSPORT deposition re-emission Hg(0) Hg(II) reduction SURFACE RESERVOIRS (Ocean, Land) microbes MeHg Methylmercury TOXIC

  18. ELEMENTAL MERCURY IS GLOBALLY DISTRIBUTED IN ATMOSPHERE Human emission (2006) Mean Hg(0) concentration in surface air: circles = observed, background = model Transport around northern mid-latitudes: 1 month Transport to southern hemisphere: 1 year Streets et al. [2009]; Soerensen et al. [2010]

  19. High-temperature combustion emits both Hg(0) and Hg(II) LOCAL POLLUTION INFLUENCE FROM EMISSION OF Hg(II) 60% Hg(0) GLOBAL MERCURY POOL Photoreduction? 40% Hg(II) NEAR-FIELD WET DEPOSITION Hg(II) concentrations in surface air: circles = observed, background=model MERCURY DEPOSITION “HOT SPOT” Large variability of Hg(II) implies atmospheric lifetime of only days against deposition Thus mercury is BOTH a global and a local pollutant! Selin et al. [2007]

  20. MERCURY WET DEPOSITION FLUXES,2004-2005 Circles: observations Background: GEOS-Chem model Model contribution from North American anthropogenic sources Model contribution from external sources Selin and Jacob [2008]

  21. SOURCE ATTRIBUTION FOR U.S. MERCURY DEPOSITION % contribution of North American sources to annual total mercury deposition Legacy anthropogenic re-emitted from soil and ocean on centurial time scale (17%) Natural (32%) North American anthropogenic (20%) Rest of world anthropogenic (31%) Selin and Jacob [2008]

  22. Historical inventory of global anthropogenic Hg emissions • Large legacy contribution from N. American and European emissions; Asian dominance is a recent phenomenon • Time integrals of global emissions imply that legacy reservoirs are not globally enriched relative to the surface Streets et al. , submitted

  23. Observed decrease of total gaseous Hg (TGM) since 1996 20-38% worldwide decrease Slemr et al. [2011] • Explanation by decline of legacy emissions would imply much higher past emissions than in Streets et al. historical inventory • Faster atmospheric oxidation of Hg(0) does not seem likely

  24. Disposal of Hg in commercial products: a missing source of legacy anthropogenic Hg? David Streets, unpublished • Hg use peaked in the 1970s: fungicide, batteries, thermometers,… • discarded Hg would enter the environment through incineration, wastewater, emission/leakage from landfills • The 1996-present decline in atmospheric concentrations could reflect the transfer of this Hg from surface reservoirs to more stable geochemical reservoirs

  25. Anthropogenic perturbation to the global Hg cycle GEOS-Chem model natural atmosphere + present-day human enhancement Primary emissions x7 Atmospheric deposition x3 Surface ocean x3 Soil +15% Deep ocean + 15% Selin et al. [2008]; Selin [2009]

  26. February 2009: Governing Council of UNEP agrees on need for global legally binding instrument on mercury • Goal is to complete negotiations by 2013 • In US; Clean Air Mercury Rule (CAMR) to reduce power plant emissions was struck down by courts in 2008; new effort is underway TOWARDS A GLOBAL MERCURY TREATY:Focus activity of United Nations Environmental Program (UNEP) • CHALLENGES: • How to regulate in the face of considerable uncertainty? • How to account for legacy mercury from past US and European emissions? • How to account for possible major effects of climate change?

More Related