Updated Dust-Iron Dissolution Mechanism: Effects Of Organic Acids, Photolysis, and Dust Mineralogy

Transcription

1 Updated Dust-Iron Dissolution Mechanism: Effects Of Organic Acids, Photolysis, and Dust Mineralogy Nicholas Meskhidze & Matthew Johnson First International Workshop on the Long Range Transport and Impacts of African Dust on the Americas 6 8 October, 2011, San Juan, PR

2 Importance of Mineral Dust Deposition to Ocean Biological Productivity A large uncertainty in predicting climate change at 2100 lies in the uncertainties associated with feedbacks in the C-cycle and aerosol forcing Today it is widely acknowledged that climate models with ocean biogeochemistry do superior job predicting CO 2 levels Ocean biological productivity (thus CO 2 uptake) can be strongly modified by aerosol inputs of iron (Fe), phosphorus (P) and other micronutrients Saharan dust is the largest single source of new Fe and P deposited to the surface ocean Nutrient dissolution in dust is a complex process; at the source regions soluble fractions of these nutrients are small (<<1%) but can be modified considerably during atmospheric transport

3 The Main Pathways of Atmospheric Transport and Deposition of Sol-Fe to the Oceans Uptake of trace gases of anthropogenic and biogenic origin (i.e., SO 2, VOCs) Hydration Production of hygroscopic organic acids (i.e., oxalic and acetic) through the cloud processing of isoprene and accelerated dissolution of mineral Fe in acidic cloud water solution (3) Evaporation (3) Heterogeneous uptake of urban/industrial air pollutants (i.e., SO 2,NO x ) Deliquescence Dissolution of Fe in resultant acidic solution (2) Anthropogenic Fe: Biomass burning, industrial emissions (1) Prescribed Bioavailable Fe 1-10% (1) (2) Mineral dust emission (i.e., Mineral quartz, dust feldspars, emission clays, (i.e., hematite) carbonate, hematite) 1 to 9 days Removal via wet and dry deposition Continents Marine Ecosystems

4 Factors Controlling Mineral Iron Dissolution During Atmospheric Transport Soil mineralogy at the source region (9 minerals) Forms of Fe minerals (hematite- -Fe 2 O 3, goethite- - FeO(OH), clays) Initial soluble Fe fraction (readily released Fe) Temperature Relative humidity Cloud cycling Abundance/deposition of acidic trace gases Oxalate promoted dissolution of Fe(III) oxides Photochemical cycling of Fe(II)-Fe(III) Pyrogenic (biomass burning and combustion) sources of Fe

5 Implementation of Fe(III) and Fe(II) Redox Cycling Kinetics Photolysis [Johnson & Meskhidze, in. prep]

6 GEOS-Chem/DFeS (v ) Model 3-D Global Chemistry Transport Model Developed at Harvard University and other institutions around the world Full chemistry configuration SMVGEAR II chemistry solver package GEOS-5 meteorology Goddard Earth Observing System (GEOS) of the NASA Global Modeling Assimilation Office Detailed emission inventories Fossil fuel, biomass burning, biofuel burning, biogenic and anthropogenic aerosol emissions State-of-the-art transport (TPCORE) and photolysis (FAST J) routines 2⁰ x 2.5⁰ grid resolution 47 vertical grids Mineral Dust and Sol-nutrient Treatment DEAD emission scheme GOCART source function Mineral dust diameter boundaries , , and μm Soluble iron (Sol-Fe) dissolution GEOS-Chem/DFeS with prognostic acidbased dust-fe dissolution scheme (Solmon et al., 2009; Johnson et al., 2010) Fe(II)/Fe(III) redox cycling Organic (oxalate) promoted Fe dissolution Photochemistry Different Fe containing minerals Soluble phosphorus (Sol-P) dissolution Acid based [Nenes et al., 2011] Seven major individual dust sources North Africa, South Africa, North America, Asia, Australia, the Middle East, and South America

7 Synergistic Methods of Active and Passive Remote Sensing and Model Simulations of Dust CALIPSO dust aerosol GEOS Chem dust aerosol CALIPSO dust AOD Application of modeled and remotely sensed data Influence of synoptic meteorological patterns on mineral dust transport and deposition [Johnson et al., 2011, ACP]

8 Dust Deposition and Possible Biological Influence January February 2009 Prognostic model calculations of leachable Fe fluxes can be used for chlorophyll production estimates Minimal influence in regions with remotely sensed [Chl a] > 1 mg m 3 Mineral dust deposition could support the background concentrations of [Chl a] [Johnson et al., 2011, ACP]

9 Difference in Sol-Fe Deposition (new old) January 2009 Considerable increase in longrange transported sol Fe deposition July 2009 μg m 2 day 1 Global increase in oceanic sol Fe deposition was ~40% and 10% for January and July 2009, respectively Sol Fe fractions in deposited dust can be up to 10%, closer to some measured values μg m 2 day 1

10 Fe(III) and Fe(II) Daily-averaged Column Burden (Aug 27-Sep 24, 2007) Fe(II) pmol m 3 Fe(III) Daily averaged Cloud Fraction R = 0.70 NMB(%) = 10.3 Obs GEOS Chem [Trapp et al., 2010]

11 Effect of Iron Minerals on Sol-Fe Column Burden Hematite Goethite μg m (July 2009) Baseline (hematite) sol Fe Goethite dissolution produces an 8% increase in sol Fe 10 μg m 2 Clays Clay mineral dissolution produces a 25% increase in sol Fe 10 μg m 2

12 Fraction of Total Sol-Fe Column Burden January 2009 April 2009

13 Conclusions and Future Research We have developed the state-of-the-art mineral-fe dissolution module and implemented it in GEOS-Chem Improvements: source mineralogy, individual source treatment of Fe dissolution, organics (oxalate) promoted Fe dissolution, photochemistry, Fe(II) Fe(III), and acid based P-dissolution There are considerable differences between prognostic and diagnostic dissolution-precipitation mechanisms Unique opportunity for the coupled climate models Comprehensive comparisons of models to observations of dust chemical composition More ambient and laboratory measurements of sol-fe in mineral dust aerosols In-situ studies for the effect of dust on ocean biogeochemistry

14 Additional Slides

15 Atmospheric Fe Dissolution Scheme Goethite ph based Dissolution Clays Anthropogenic forms of Fe

16 Daily-averaged Sol-Fe Deposition January 2009 July 2009

17 Surface Fe(III) and Fe(II) Concentration

18 Annual Total Sol-P Deposition Present Study Mahowald et al., mg m 2 Annual sol P deposition extrapolated from January 2009 deposition fluxes Deposition fluxes are comparable to past studies Deposited sol P fraction up to ~60% mg m 2