Chemical Modification of

Airborne Mineral Dust

Vicki H. Grassian !Department of Chemistry

University of Iowa

HealthMineral dust aerosol in the

respirable size range can cause

health problems

Mineral Dust

Biogeochemical CycleDeposited mineral dust

aerosol containing iron can

be a major source of iron in

the oceans

ChemistryMineral dust aerosol can alter

the chemical balance of the

atmosphere through surface

adsorption and reaction

ClimateMineral dust aerosol can alter

the Earth’s temperature through

direct and indirect climate

forcing

Mineral Dust – An Abundant Aerosol in the Troposphere"

With Global Implications"

Mineral Dust – An Abundant Aerosol in the Troposphere"Asian Dust Storm!

African Dust Storm!

long-range transport, atmospheric aging

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.!

mineral dust!ozone, nitrogen oxides.

sulfur oxides, organics!

•1000-3000 Tg of mineral aerosol is injected into the atmosphere!

•Because of long range transport, mineral aerosol will impact both local and distant regions!

Particulate NO3

HONO NO NO2

HNO3 N2O5 NO3

Particulate SO4 Dissolved Oxidants

O3

HO2,RO2

OH, RO

H2SO4

PAN, PPN

VOC

H2O2

PA, PP CO, CO2

h!" h!"

h!" h!"

h!"

h!"

h!"

O3, RO2

OH

OH

H2O

OH

OH

O3

O3

NO

O3

SO2

SO2

HO2

H2O

CO

multiple steps

multiple steps

Impact of Dust on

Atmospheric Chemistry !

!

Reactions of Trace

Atmospheric Gases!

with Mineral Dust Aerosol!

Grassian, J. Phys. Chem. A 2002, 106, 860-877

Reactions on Mineral Dust Aerosol

HealthMineral dust aerosol in the

respirable size range can cause

health problems

Mineral Dust

Biogeochemical CycleDeposited mineral dust

aerosol containing iron can

be a major source of iron in

the oceans

ChemistryMineral dust aerosol can alter

the chemical balance of the

atmosphere through surface

adsorption and reaction

ClimateMineral dust aerosol can alter

the Earth’s temperature through

direct and indirect climate

forcingThis Heterogeneous

Chemistry has the Potential

to Alter the Impacts of

Mineral Dust on Climate,

Atmospheric Chemistry,

Biogeochemistry and Health

Mineral Dust

Particle

Mineralogy Source Region

Atmospheric

Gas

Molecular Species Composition of Air Mass

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?

Dust Mineralogy

What are the Differences Between

Asian Dust (World’s Second Largest Dust Source)

vs

African Dust (World’s Largest Dust Source)

Top cluster/type for African dust (sampled in Puerto Rico) and Asian dust (sampled in Gosan, Korea)

ATOFMS of African and Asian Dust Moving Away From Sources

and Toward the Americas

Data From Kimberly Prather and Liz Fitzgerald at UCSD

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)

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

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*

But There Are Differences Between Dust Sources in Asia

And What About Africa –

Also large variability

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?"

!

"

0

10

20

30

40

50

60

0 200 400 600 800

< 1 % RH

20 % RH

40 % RH

60 % Rh

Ozo

ne c

on

cen

tra

tio

n,

pp

m

Time (minutes)

t=0,

aerosol introduction

Often Studies of Mineral Dust Aerosol are Done from the Gas-Phase

Perspective: Ozone Uptake on Mineral Dust, #-Fe2O3, as f(RH)"Environmental Aerosol Reaction Chamber"

Kinetic rate!

decreases as a!

f(RH), change in

kinetics as a f(RH)!

!

-0.05

0

0.05

0.1

0.15

0.2

0.25

10001500200025003000350040004500

A

b

s

o

r

b

a

n

c

e

Wavenumber (cm-1)

Ozone

1043

Iron Oxide

H2O

Collaborators Mark Young

and Paul Kleiber!

Ozone Uptake on Mineral Dust, #-Fe2O3 Decreases

As Adsorbed Water coverage Increases"

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"

Water Adsorption at 298 K as a f(RH)!

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

HNO3, O3, SO2,

NO2 and N2O5

Deactivation of ice nuclei due to atmospherically relevant surface coatings,

Cziczo, Froyd, Gallavardin, Moehler, Benz, Saathoff and Murphy Environ. Res.

Lett. Vol. 4, 044013, 2009.

Importance of adsorption for CCN activity and hygroscopic properties of mineral

dust aerosol, Kumar, Nenes and Sokolik Geophysical Res Letts Vol. 36 L24804,

2009.

Additionally There is Chemical Modification of Mineral

Dust Aerosol "

Particles Can Transform From Solid to Liquid Particles as they Undergo

Heterogeneous Reactions as a f(RH) !

CaCO3 Ca(NO3)2

Clearly Reactions Can Impact the Properties of the Aerosol!

Collaborator –

Dr. Alex Laskin

Aerosol Perspective: Reactions Leading to Soluble Coatings Alter Aerosol Climate

Properties (Optical Properties - size and composition; CCN and IN properties) "

1000200030004000500060007000

Wavenumber (cm-1)

0.005

RH=63%

RH=8%

Extinction

! (H2O)

" (H2O)

1000200030004000500060007000

0.01

RH=3%

RH=63%

Extinction

Wavenumber (cm-1)

B. IR Extinction Spectra at Different

%RH

C. Particle Size Changes as f(%RH) after reaction

A. Heterogeneous Chemistry: Carbonate

to Nitrate Conversion

Carbonate particles (before reaction)

Hygroscopic growth of carbonate and nitrate particles

Nitrate particles (after reaction)

Carbonate particles (before reaction)

Nitrate particles (after reaction)

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0 20 40 60 80 100

Ca(NO3)2

Kohler Curve Ca(NO3)2

CaCO3

g(RH) = 1

Gro

wth

Fac

tor

(Dp/D

0)

% RH

Chemistry is

Mineralogy

Specific

Gassó, S.;

Grassian, V.H.;

Miller, R.L.,

!Impacts of Dust

on Climate and

Oceans"#Elements

2010, 6, 247-253."

These soluble

coatings

enhance CCN

activity.

Comparison of Reactive Uptake of Asian Dust

and African Dust with Nitrogen Oxides

Chemistry?

Chemistry of Carbonate Minerals (Mineralogy) Gives

Enhanced Reactivity for Asian Dust Sample?

!NO2 !HNO3

Saharan

Sand 1"10

-6 2"10

-5

China Loess 4.4"10-5

1.1"10-3

Asian:African 44 55

Chemistry and Photochemistry of Adsorbed Nitric Acid on

Other Components of Mineral Dust – Al2O3 Particle Surfaces

1. Nitric Acid Adsorption on Al2O3, f(RH) !

Photochemistry of Adsorbed Nitrate

•!Great deal of ammonia in the atmosphere!

•!Ammonium nitrate a well known aerosol that forms under certain conditions!

! ! ! HNO3 + NH3 ! !NH4NO3 !!

2. Adsorbed Nitric Acid and Ammonia"

•!Adsorbed nitrate forms on the surface only!

•!Adsorbed water solvates nitrate ions at the oxide interface!

Photochemistry of Ammonium Nitrate Coatings

!

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!

! ! ! !

•!The molecular/electronic structure of the nitrate ion is highly dependent on the !environment/

symmetry"

Light Absorbing Components of Mineral Dust Aerosol Include

Titanium Dioxide (well-known photocatalyst) and Iron Oxides

! ! ! NO3- + H+ ! !NO2 + OH !

! ! ! !NO3- ! ! NO2

- + O(3P) !!

h!

h!

1600180020002200Wavenumber (cm-1)

420 min

120 min

30 min

0 min

N2O

2224

NO1874

0.005(b) Gas Phase

100012001400160018002000

Absorbance

Wavenumber (cm-1)

0.1

14121340

1046

(a) Surface

420 min

120 min

30 min0 min

1633

!(H2O)

"1(NO

3-)

"3(NO

3-)

FTIR Analysis of Surface and Gas

Phase as a f(time)

Surface Photochemistry (%> 300 nm) of Nitrate on Aluminum Oxide

Particle Surfaces Under Various Conditions: Relative Humidity

Heterogeneous Photochemistry is Complex and the Laboratory Data

Suggests Potentially A Mechanisms for Nitrate to NOx"

Rubasinghege, G.; Grassian, V. H. !Photochemistry of

Adsorbed Nitrate on Aluminum Oxide Particle Surfaces"#

Journal of Physical Chemistry A 2009, 113, 7818-7825.!

RH dependence of gas-

phase product formation

Proposed mechanism for formation of products

Comparison of Reactivity of Asian Dust and

African Dust with Nitrogen Oxides Chemistry?

-Formation of Nitrates Due to Higher Levels of NOx

and HNO3 (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?

Sources of Authentic and Complex Dust

Samples

China Loess

Na

Mg

Al

Si

K

Ca

Ti

V

Mn

Fe

Ni

Coastal Saudi

Na

Mg

Al

Si

K

Ca

Ti

V

Mn

Fe

Ni

Inland Saudi

Na

Mg

Al

Si

K

Ca

Ti

V

Mn

Fe

Ni

Inland Saudi

(8.7% Fe)

Saudi Beach

(3.0% Fe) Saharan Sand

Na

Mg

Al

Si

K

Ca

Ti

V

Mn

Fe

Ni

Saharan

(5.1% Fe)

China Loess

Na

Mg

Al

Si

K

Ca

Ti

V

Mn

Fe

Ni

China Loess

(7.2% Fe) Arizona Road DustNa

Mg

Al

Si

K

Ca

Ti

V

Mn

Fe

Ni

Arizona Road Dust

(3.3% Fe)

•!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.

Mineral dust hypotheses for !

laboratory dissolution studies on Fe-containing dust!

Chemical Reactions Can Play a Role in Fe

Availability (solubility)

Fe-containing "

dust"

SO2"

HNO3"

Organics"

O3"

h!"

Environment favors

redox cycling!

(acidic, h!, reductants,

oxidants) !

Fe(II)(aq) or"

Fe(II)(ads)"

Oxidant"

(O3, O2)"

Reductant"

(SO2, RH)"

Fe(III)(s)"

Acidic environment

(due to HNO3; pH ~ 1)

Meskhidze et al.,

GRL,

2003

Gobi desert

Shanghai Yellow Sea

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, H2SO4, HNO3)- simulate proposed

!atmospheric conditions" !

Analytical Method:!Fe(II) and total dissolved

Fe from !

1,10-phenanthroline!

UV-vis at l = 510 nm!

NN

Dissolution at

pH 1 (HNO3)!Arizona Road Dust (AZRD)!

Saudi Beach Sand (SBS)!

Inland Saudi Sand (ISS)!

Saharan Sand (SS)!

Results: Iron Dissolution in Authentic Dust

Samples!

These results don$t

correlate with any

simple physical

descriptors including

%Fe in samples

surface area,…). !

Arizona Road Dust - particle(s) with no Fe !

Elemental Maps Show Heterogeneity of !

Particles and Samples!

Al

Ca

MgSEM

Fe

Si

ONa

Arizona Road Dust - particle with Fe associated with Si and Al!

Arizona Road Dust - particle with high Fe content !

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.!

What about Size Effects: Comparison of the

Dissolution of #-FeOOH Nanorods and Microrods"

7 x 80 nm

Nanorods

Microrods

25 x 670 nm

Time (h)

900

600

300

0 0 10 20 30 40 50

Dis

solv

ed

Fe

(III

) (

M.g

)

Nanorods

Microrods

9

6

3

0 0 10 20 30 40 50

Dis

solv

ed

Fe

(III

) (

M.c

m)

Nanorods

Microrods

Time (h)

(a) (b)

Similar Enhanced Dissolution of Nanorods Relative to

Microrods in low pH Environments (pH 2)

per mass basis per surface area basis

Three-fold enhancement beyond surface area effects!!

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. 41 2007, 7166-7179

Complexity Arises from the Different Surface Complexes that Form, Different Solution Phase

Complexes that Form and the Different Photochemistry of these Complexes

Anion Plays a Role in the Acid-Assisted Dissolution of Fe-

Containing Dust

Rubansinghege, Lentz, Scherer and Grassian, PNAS, 2010

Dust Mineralogy and Shape Impacts Optical Properties of

Mineral Dust Aerosol

IR Extinction Spectra: Experimental and Calculated Using Mie Theory

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

Mie theory, a theory for light absorption and scattering by spheres that requires two inputs, particle size and optical constants.

Yet Mie theory is widely used for interpreting remote sensing.

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.

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 NOx and HNO3 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

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