Chemical Modification of Airborne Mineral Dust

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1 Chemical Modification of Airborne Mineral Dust Vicki H. Grassian! Department of Chemistry University of Iowa

2 Mineral Dust An Abundant Aerosol in the Troposphere" With Global Implications" Climate Mineral dust aerosol can alter the Earth s temperature through direct and indirect climate forcing Biogeochemical Cycle Deposited mineral dust aerosol containing iron can be a major source of iron in the oceans Mineral Dust Chemistry Mineral dust aerosol can alter the chemical balance of the atmosphere through surface adsorption and reaction Health Mineral dust aerosol in the respirable size range can cause health problems

3 Mineral Dust An Abundant Aerosol in the Troposphere" Asian Dust Storm! long-range transport, atmospheric aging mineral dust! ozone, nitrogen oxides. sulfur oxides, organics! African Dust Storm! Atmospheric aerosols undergo heterogeneous chemistry " as they are transported through the atmosphere. " " These reactions cause Chemical Modification of the Atmosphere as well as Chemical Modification of the Airborne Mineral Dust Particles. These reactions have global implications.! Tg of mineral aerosol is injected into the atmosphere! Because of long range transport, mineral aerosol will impact both local and distant regions!

4 Impact of Dust on Atmospheric Chemistry!! Reactions of Trace Atmospheric Gases! with Mineral Dust Aerosol! Grassian, J. Phys. Chem. A 2002, 106, h!" h!" HONO NO NO 2 PAN, PPN VOC multiple steps H 2 O CO PA, PP CO, CO 2 multiple steps O 3, RO 2 HO 2,RO 2 OH HNO N 2 O 5 3 H 2 O NO 3 h!" h!" O 3 OH h!" NO OH h!" O 3 h!" O 3 OH, RO O 3 SO 2 HO 2 OH SO 2 H 2 SO 4 H 2 O 2 Dissolved Oxidants Particulate SO 4 Particulate NO 3

5 Reactions on Mineral Dust Aerosol Mineral Dust Particle Mineralogy Source Region Atmospheric Gas Molecular Species Composition of Air Mass This Heterogeneous Chemistry has the Potential to Alter the Impacts of Mineral Dust on Climate, Atmospheric Chemistry, Biogeochemistry and Health Biogeochemical Cycle Deposited mineral dust aerosol containing iron can be a major source of iron in the oceans Climate Mineral dust aerosol can alter the Earth s temperature through direct and indirect climate forcing Mineral Dust Health Mineral dust aerosol in the respirable size range can cause health problems Chemistry Mineral dust aerosol can alter the chemical balance of the atmosphere through surface adsorption and reaction

6 Some Examples of the Chemical Modification of Mineral Dust Aerosol During Heterogeneous and Multiphase Chemistry Heterogeneous and Multiphase Chemistry of Mineral Dust Can Result in Surface Coatings with Secondary Species Containing Chromophores that Can Be Activated with Sunlight Thus Modifies the Photochemical Activity of Atmospheric Dust (Nitrate Photolysis) Heterogeneous and Multiphase Chemistry of Mineral Dust Can Result in Surface Coatings that Modify the Climate-Relevant Properties of the Dust (CCN Activity, IN Activity and Light Scattering) Heterogeneous and Multiphase Chemistry of of Iron-Containing Dust Can Impact Ocean Biogeochemistry (Changes in Iron Dissolution) Is this happening similarly for both African and Asian Dust?

7 Dust Mineralogy What are the Differences Between Asian Dust (World s Second Largest Dust Source) vs African Dust (World s Largest Dust Source)

8 ATOFMS of African and Asian Dust Moving Away From Sources and Toward the Americas Data From Kimberly Prather and Liz Fitzgerald at UCSD Top cluster/type for African dust (sampled in Puerto Rico) and Asian dust (sampled in Gosan, Korea) Comparison Shows! Asian dust More Ca and Mg-containing dust! More processed dust (especially w/ nitrate)! More bio-marker ions!!! African dust More Aluminosilicates and Quartz Less processed dust Shows more signs of being mixed with sea salt (via cloud processing)

9 Elemental Analysis of Mineral Particles from 0.1 to 5 µm For Four Different Dust Source Regions Percentage of Ca-containing particles in Four Samples

10 But There Are Differences Between Dust Sources in Asia Single-Particle Mineralogy of Chinese Soil Particles by the Combined Use of Low-Z Particle Electron Probe X-ray Microanalysis and Attenuated Total Reflectance-FT-IR Imaging Techniques ANALTYICAL CHEMISTRY - ASAP Md Abdul Malek, BoWha Kim, Hae-Jin Jung, Young-Chul Song, and Chul-Un Ro* And What About Africa Also large variability

11 Our Approach To Understanding Chemical Modifications of Mineral Dust Aerosol! Study the Heterogeneous Chemistry of the Components of Mineral Dust Aerosol to Determine the Impact on the Gas Phase (Gas-Phase Perspective)" "-clays: kaolinite, illite and montmorillinite" -oxides: hematite, goethite, quartz, corundum" -carbonates: calcite, dolomite" As well as complex dust mixtures: with extensive characterization"! Design and Perform a Series of Laboratory Measurements so as to Better Understand Chemical Modifications of Mineral Dust (Aerosol Perspective) and How they May Impact the Properties of Mineral Dust Especially Related to! "- Continued Chemistry" " "Are new heterogeneous pathways available? " "-Climate Impact of Mineral Dust" " "How do climate-relevant properties change?" "-Ocean Biogeochemistry" " "For Fe-containing mineral dust, what is the impact on Fe dissolution?" "

12 Often Studies of Mineral Dust Aerosol are Done from the Gas-Phase Perspective: Ozone Uptake on Mineral Dust, #-Fe 2 O 3, as f(rh)" Environmental Aerosol Reaction Chamber" A b s 0.15 o r 0.1 b a 0.05 n c e 0 Iron Oxide H 2 O Ozone 1043 Collaborators Mark Young and Paul Kleiber! Wavenumber (cm -1 ) Ozone concentration, ppm t=0, aerosol introduction < 1 % RH 20 % RH 40 % RH 60 % Rh Kinetic rate! decreases as a! f(rh), change in kinetics as a f(rh)!! Time (minutes)

13 Ozone Uptake on Mineral Dust, #-Fe 2 O 3 Decreases As Adsorbed Water coverage Increases" Water Adsorption at 298 K as a f(rh)! Water layer, even at high water coverages, never completely inhibits reactivity suggesting water coverage is not uniform on the surface and active sites (Lewis acid sites) are still available for reaction"

14 The Importance of These Heterogeneous Reactions on Mineral Dust Aerosol in Atmospheric Chemistry Can Be Determined by Incorporating Laboratory Data into Atmospheric Models Currently Models Are Being Updated to Include Mineral Dust Components and Relative Humidity Dependence HNO 3, O 3, SO 2, NO 2 and N 2 O 5

15 Additionally There is Chemical Modification of Mineral Dust Aerosol " Importance of adsorption for CCN activity and hygroscopic properties of mineral dust aerosol, Kumar, Nenes and Sokolik Geophysical Res Letts Vol. 36 L24804, Deactivation of ice nuclei due to atmospherically relevant surface coatings, Cziczo, Froyd, Gallavardin, Moehler, Benz, Saathoff and Murphy Environ. Res. Lett. Vol. 4, , Particles Can Transform From Solid to Liquid Particles as they Undergo Heterogeneous Reactions as a f(rh)! CaCO 3 Ca(NO 3 ) 2 Collaborator Dr. Alex Laskin Clearly Reactions Can Impact the Properties of the Aerosol!

16 Aerosol Perspective: Reactions Leading to Soluble Coatings Alter Aerosol Climate Properties (Optical Properties - size and composition; CCN and IN properties) " A. Heterogeneous Chemistry: Carbonate to Nitrate Conversion B. IR Extinction Spectra at Different %RH C. Particle Size Changes as f(%rh) after reaction Carbonate particles (before reaction) Carbonate particles (before reaction) Chemistry is Mineralogy Specific E x t i n c t i o n RH=63% RH=3% Wavenumber (cm -1 ) 1000 Nitrate particles (after reaction) These soluble coatings enhance CCN activity. E x t i n c t i o n 7000 Nitrate particles (after reaction)! (H 2 O) " (H 2 O) RH=63% RH=8% Wavenumber (cm -1 ) Growth Factor (D p /D 0 ) Hygroscopic growth of carbonate and nitrate particles Ca(NO 3 ) 2 Kohler Curve Ca(NO 3 ) 2 CaCO 3 g(rh) = % RH Gassó, S.; Grassian, V.H.; Miller, R.L.,!Impacts of Dust on Climate and Oceans"#Elements 2010, 6, "

17 Comparison of Reactive Uptake of Asian Dust and African Dust with Nitrogen Oxides Chemistry? Saharan Sand! NO2! HNO3 1"10-6 2"10-5 China Loess 4.4" "10-3 Asian:African Chemistry of Carbonate Minerals (Mineralogy) Gives Enhanced Reactivity for Asian Dust Sample?

18 Chemistry and Photochemistry of Adsorbed Nitric Acid on Other Components of Mineral Dust Al 2 O 3 Particle Surfaces 1. Nitric Acid Adsorption on Al 2 O 3, f(rh)!!adsorbed nitrate forms on the surface only!!adsorbed water solvates nitrate ions at the oxide interface! Photochemistry of Adsorbed Nitrate 2. Adsorbed Nitric Acid and Ammonia"!Great deal of ammonia in the atmosphere!!ammonium nitrate a well known aerosol that forms under certain conditions!!!!! HNO 3 + NH 3!!NH 4 NO 3! Photochemistry of Ammonium Nitrate Coatings

19 Light Absorbing Components of Mineral Dust Aerosol Include Titanium Dioxide (well-known! photocatalyst) and Iron Oxides Heterogeneous and Multiphase Chemistry of Mineral Dust Aerosol Can Cause Photochemically Inactive Components of Dust to Become Photochemically Active!! -Day Time Chemistry of Mineral Dust Can Be Quite Different Than Night Time Chemistry-!! Chromophores associated with mineral dust aerosol include adsorbed nitrate, nitrite and organics (humic)!!!for nitrate there are two electronic transitions n-$* (~295 nm) and $- $* (~200 nm)!!nitrate is the dominant absorber of UV light in natural waters and has interesting photochemistry!!!!!!! NO -! 3 + H + h!!!no 2 + OH!!!!!NO - 3! h!! NO O( 3 P)!!!The molecular/electronic structure of the nitrate ion is highly dependent on the!environment/ symmetry"

20 Surface Photochemistry (%> 300 nm) of Nitrate on Aluminum Oxide Particle Surfaces Under Various Conditions: Relative Humidity A b s o r b a n c e (a) Surface 0 min 30 min 120 min 420 min!(h 2 O) 1633 " 3 (NO 3 - ) " 1 (NO - 3 ) 1046 (b) Gas Phase N 2 O 2224 NO min 30 min 120 min 420 min FTIR Analysis of Surface and Gas Phase as a f(time) Wavenumber (cm -1 ) Wavenumber (cm -1 ) 1600

21 Heterogeneous Photochemistry is Complex and the Laboratory Data Suggests Potentially A Mechanisms for Nitrate to NOx" RH dependence of gasphase product formation Proposed mechanism for formation of products Rubasinghege, G.; Grassian, V. H.!Photochemistry of Adsorbed Nitrate on Aluminum Oxide Particle Surfaces"# Journal of Physical Chemistry A 2009, 113, !

22 Comparison of Reactivity of Asian Dust and African Dust with Nitrogen Oxides Chemistry? -Formation of Nitrates Due to Higher Levels of NO x and HNO 3 (Composition of Air Mass) in Asian Dust Plume: -Nitrate Photochemistry Causes a Decrease in Nitrate on the Surface More Efficient Nitrate Photochemistry on African Dust?

23 Na Mg Al Si K Ca Ti V Mn Fe Ni Sources of Authentic and Complex Dust Samples Saharan (5.1% Fe) Arizona Road Dust (3.3% Fe) Inland Saudi (8.7% Fe) China Loess (7.2% Fe) Saudi Beach (3.0% Fe)

24 Mineral dust hypotheses for! laboratory dissolution studies on Fe-containing dust!!fe speciation will vary with source region and this will influence the reactivity (redox, dissolution) of Fe-containing minerals.!atmospheric processing of Fe-containing minerals 3 will increase Fe dissolution through the formation of Fe(II) species and more labile Fe(III) solid phases.!nanoparticulate iron phases will exhibit enhanced redox reactivity and increased dissolution.

25 Chemical Reactions Can Play a Role in Fe Availability (solubility) Fe-containing " dust" SO 2" HNO 3" Organics" O 3" h!" Environment favors redox cycling! (acidic, h!, reductants, oxidants)! Gobi desert Shanghai Yellow Sea Oxidant" (O 3, O 2 ) " Fe(III)(s) " Meskhidz e et al., GRL, 2003 Reductant" (SO 2, RH) " Acidic environment (due to HNO 3 ; ph ~ 1) Fe(II)(aq) or" Fe(II)(ads) "

26 Experimental Protocol: Iron Dissolution in Authentic Dust Samples! Batch Reactors:! Dark reactions! Solids loading: 2-4 g/l (initial expts), 12.5 g/l (later expts)! Mixed end-over-end: 45 RPM! 0.1 M NaCl electrolyte for ionic strength! Low ph 1 (0.1 M HCl, H 2 SO 4, HNO 3 )- simulate proposed!atmospheric conditions"! Analytical Method:! Fe(II) and total dissolved Fe from! 1,10-phenanthroline! UV-vis at l = 510 nm! NN

27 Results: Iron Dissolution in Authentic Dust Samples! Dissolution at ph 1 (HNO 3 )! Arizona Road Dust (AZRD)! Saudi Beach Sand (SBS)! Inland Saudi Sand (ISS)! Saharan Sand (SS)! These results don$t correlate with any simple physical descriptors including %Fe in samples surface area, ).!

28 Elemental Maps Show Heterogeneity of! Particles and Samples! Arizona Road Dust - particle(s) with no Fe! Arizona Road Dust - particle with high Fe content! Arizona Road Dust - particle with Fe associated with Si and Al! Fe Ca Si SEM Mg Al Na O

29 Understanding Fe-chemistry through Spectroscopic Studies and Single Particle Analysis! These results suggest that Fe present as Fe(II) and Fe(III) substituted into aluminosilicate clays may be more important in iron dissolution than other iron phases.!

30 What about Size Effects: Comparison of the Dissolution of #-FeOOH Nanorods and Microrods" Nanorods 7 x 80 nm Microrods 25 x 670 nm

31 Similar Enhanced Dissolution of Nanorods Relative to Microrods in low ph Environments (ph 2) Dissolved Fe (III) ( M.g ) per mass basis (a) 900 Nanorods Microrods Time (h) Dissolved Fe (III) ( M.cm ) per surface area basis 9 (b) Nanorods 6 Microrods Time (h) Three-fold enhancement beyond surface area effects!!

32 Role of Anion in Acid Dissolution - Complex Field studies using single particle analysis have shown that mineral dust aerosol can be associated with nitrate, sulfate and chloride Mineral dust is a sink for chlorine in the marine boundary layer Sullivan RC, Guazzotti SA, Sodeman DA, Tang YH, Carmichael GR, Prather KA Atmos. Env , Anion Plays a Role in the Acid-Assisted Dissolution of Fe- Containing Dust Complexity Arises from the Different Surface Complexes that Form, Different Solution Phase Complexes that Form and the Different Photochemistry of these Complexes Rubansinghege, Lentz, Scherer and Grassian, PNAS, 2010

33 Dust Mineralogy and Shape Impacts Optical Properties of Mineral Dust Aerosol IR Extinction Spectra: Experimental and Calculated Using Mie Theory Mie theory, a theory for light absorption and scattering by spheres that requires two inputs, particle size and optical constants. Resonance Region for Clays and Quartz Aerosol Due to the n(si-o) stretch Comparison of calculated and experimental spectra show that shape effects are important to include and improve the overall agreement Yet Mie theory is widely used for interpreting remote sensing.

34 Implications for satellite data retrieval!!! Satellite determinations of, e.g., surface temperature or atmospheric ozone concentrations, are often obtained by measuring the spectrum of outgoing terrestrial radiation. This analysis must account for effect of atmospheric dust. To measure dust loading and composition, some satellites use narrow band IR sensors.

35 Chemical Modification of Airborne Mineral Dust African versus Asian Dust Transported Toward Americas 1.! Differences due to mineralogy complex issue 2.! Differences due to gas-phase constitutents (Asian Dust passes through Higher Local Conc. of NO x and HNO 3 on the way to Americas compared to African Dust) 3.! For all dust sources the Fe solubility correlates poorly with total Fe 4.! Details of Fe mineralogy important 5.! Fe dissolution increases in low ph environments associated with atmospheric processing and these processes may be different between Asian dust and African dust 6.! Anion effects nitrate vs chloride can also play a role, these may be different between Asian and African dust 7.! Shape also important in IR resonance region and this will impact satellite retrievals

36 Acknowledgments Funding: US National Science Foundation Current and Former Students and Postdocs Current: Gayan Rubansinghege and Olga Laskina Former: Jennifer Schuttlefield, Paula Hudson, Elizabeth Gibson, Jonas Baltrusaitis and David Cwiertny Collaborators: Mark Young, Michelle Scherer, Alexander Laskin, Paul Kleiber and Gregory Carmichael and Kimberly Prather