1. The Heterogeneous Interaction of
Atmospheric Trace Gases on Mineral
Aerosols and soot
Federico Karagulian
(Supervisor: M.J. Rossi)
Laboratoire de Pollution Atmosphérique et Sol
(LPAS), Ecole Polytechnique Fédérale de Lausanne
(EPFL), CH-1015-Lausanne (Switzerland)

2. Which kind of chemistry for atmospheric pollution?
Nitrate’s chemistry: nighttime
Ozone chemistry: daytime
Ozone forms when precursor compounds
react in the presence of sunlight and high
temperatures.
Important nitrate reactions at night
(daytime photolysis in the yellow box)

3. Atmospheric chemistry: Ozone formation in the troposphere
O 3 + hυ → O(1 D) + O 2
λ < 320 nm
H 2 O + O(1 D) → 2OH
OH + VOCs → R
Organic radical
N 2 O + O( 1 D) → 2NO
R + O 2 → RO 2
RO 2 + NO → RO + NO 2
NO 2 + hν → NO + O( 3 P)
O 2 + O( 3 P) → O 3
OH + NO 2 → HNO3
Polluted
atmosphere
HNO 3 + hν → OH + NO 2
Slow process, therefore HNO3 may represent a
reservoir for O3

4. erosion and
deforestation
Mineral dust emission
change of landusage: fire and wind
traveling with wind

5. Intense African dust storm sent a massive dust plume
westward over the Atlantic Ocean on March 2, 2003.
Images courtesy Jeffrey Schmaltz and Jacques Descloitres, MODIS Rapid Response Team, NASA GSFC Animation credit:
NASA Goddard Space Flight Center, Scientific Visualization Studio
http://svs.gsfc.nasa.gov/stories/dust_20030306/index.html

6. Izaña and Sta. Cruz de Tenerife
Normal situation
Mineral Dust events
MINATROC field campaign (July, 2002)

7. Izaña and Sta. Cruz de Tenerife
Normal situation
Mineral Dust events
MINATROC field campaign (July, 2002)

8. Environmental effects of aerosols (Particulate Matter PM):
 Soot aerosol and black carbon (BC) have a warming effect absorbing
sunlight. The contribution of BC and soot to global warming may be second
only to that of CO2. 1
 Mineral dust have a warming and cooling effect
Simulation. increasing of dust load from 4.0 x 104 to 1.3 x 105 mg / m2 brings to:
 0.04  0.21 W/m2 at the top of the atmosphere (heating)2
 -0.74 -1.82 W/m2 at the surface (cooling)2
 Absorption and scattering of UV radiation by aerosol modify the kinetics
of photochemical reactions.
 Temperature modification by aerosols modify the kinetics of chemical reactions
1
2
M.A. Jacobson, Nature vol. 409, p. 695 (2001).
S. Woodward, Geophys. Res. Lett. 32 (18) Sep 28, 2005.

9. Mineral dust events and heterogeneous chemistry
Mineral dust = mineral aerosol (‘small mineral particle’)
Size = 1 – 10 µm
O3
NOx = NO+NO2
NOy = NO3 + N2O5 +HNO3
+
=>
Reaction
products
Gas + solid reaction = heterogeneous reaction
γ=
number of molecules taken up
total number of collision
=
Probability that a molecule is taken
up on the solid substrate
(uptake coefficient)

10. Mineral dust aerosol surrogates
Real event: dust storm
Representative Samples
Model substances such as
CaCO3, Natural Limestone,
Kaolinite, Arizona Test
Dust, Saharan Dust
Heterogeneous
Reactions with
trace gases
Atmospheric consequences
a) Reduction of the
atmospheric concentration of
trace gases like
HNO3, NO3, N2O5, O3.
b) Strong influence
on the global ozone
budget

11. How does mineral dust affect atmospheric chemistry ?
HO2
O3
N2O5
NO
NO2
DUST
SO2
HNO3
OH
Global
∆(%) Bauer et al.2
NO3
∆(%) Bian and Zender 3
∆H
∆P+H
∆H
∆O3
-5.4
-0.7
-0.9
∆HNO3
-35.3
-3.5
-3.8
∆NO3
-17.7
-4.7
-5.9
∆N2O5
-10.6
0.0
-2.1
∆NO2
-1.4
+1.1
-0.3
∆OH
-6.6
-11.1
-9.6
Grey line = model simulation
Black line = field measurements 1
(Monte Cimone, 2000)
P. Bonasoni; et al., Atmos. Chem. Phys. 2004, 4, 1201-1215.
Bauer et al., J. Geophys. Res. Atm., Vol. 109, doi:10.1029/2003JD003868, 2004.
3
Bian and Zender, J. Gephys. Res. Atm, Vol 108, doi:10.1029/2002JD003143, 2003.
1
2

12. Experimental: Knudsen Flow Reactor
Experimental set up
…in the lab

13. REMPI cell
Knudsen reactor
control panel
pumping
detection chamber

14. REMPI detection of NO and NO2: λ = 252.6 nm
λ = 511 nm
Visible light emission
Molecular excitation
Pumping laser
−
NO 2 + 3hν 2 + hν 2 → NO + e
(b)
50
40
30
2
20
1
10
+
+
2
NO + 2hν 1 + 2hυ1 → NO + e
(a)
3
2
−
-3
60x10
4
Energy (mJ/cm )
+
NO REMPI signal (Volt x s)
Ions yield
Molecular photoionization
0
0
445
450
wavelength (nm)
455
460

15. Example: NO3 uptake experiment on 2 g of CaCO3
 MS detection
 NO2 REMPI detection
Multi-Diagnostic Detection
1.6
F0M
N 2O 5 → NO 2 + NO 3
T = 500 K
MS Signal (Volt)
1.4
NO3 inlet
reaction on
FrM
(a)
1.2
(b)
1.0
(a)
0.8
(b)
(c)
0.6
0.4
0.2
(d)x10
(d)x10
0.0
200
Heterogeneous rate loss
(c)
400
600
time (s)
800
1000
MS Signal: (a) = m/e 30; (b) = m/e 46;
(c) = NO2 REMPI signal at λ = 511 nm; (d) = m/e 62 (NO3)
F0M
k ss = ( M − 1) ⋅ k esc = γ ss ⋅ ω
Fr
γ ss = Steady state uptake coefficient

16. NO3 uptake on 200 mg of Kaolinite
gas residence time τ = 1/kesc = 0.57 s (orifice = 8 mm)
[NO3] = (7.0 ± 1.0) x 1011 cm-3 (30 ppb)
1.5
MS Signal (Volt)
NO2 uptake on adsorbed NO3
(a) = m/e 30; (b) = m/e 46; (c) = NO2
REMPI signal; (d) = m/e 62 NO3;
(e) = m/e 63 HNO3
reaction on
NO3 inlet
(a)
(a)
(b)
1.0
(b)
(c)
(c)
0.5
(d)x10
(d)x10
0.0
N 2 O 5(g) Determined from excess MS signal at
200
400
600
800
time (s)
(e)
1000
1200
m/e 46 after correction for NO2 REMPI signal
0.14
MS Signal (Volt)
NO 3(ads) + NO 2 → N 2 O 5(ads)
reaction on
0.12
0.10
N 2 O 5(ads) → N 2 O 5(g)
(c)
0.08
0.06
0.04
(b)x10
0.02
400
500
N 2 O5(ads) + H 2 O (ads) → 2HNO3(g)
(a) x10
(d)x10
0.00
600
700
800
time (s)
HNO3(g)

17. Proof of adsorbed NO3: NO2 REMPI detection
NO + NO 3(ads) → 2NO 2
Titration on Arizona Test Dust surface
15
Flow (molecule/s)
12
NO3
inlet
reaction on
NO3 stop
NO admission
10
reaction on
NO 2 + NO 3(ads) → 2NO 2 + 1 O 2
2
8
6
(a)
4
(b)
Saharan Dust
2
0
400
600
time (s)
NO2
800
1000
15
15x10
Flow (molecule/s)
14x10
10
NO3 stop
NO2 admission
reaction on
(b)
NO3
inlet
reaction on
5
(a)
0
600
800
time (s)
1000
1200

18. NO3 and N2O5 reaction on CaCO3 (powder calcium carbonate)
NO 3 + NO 2
CaCO 3
Formation of an intermediate
N 2 O 5(g)
adsorbed
gas phase
N 2 O 5(ads)
gas phase
CaCO 3 + H 2 O → Ca(OH)(HCO 3 )
N 2 O 5(g) + Ca(OH)(HCO 3 ) → Ca(NO 3 ) 2 + H 2 O (s) + CO 2(g)
Delayed formation of nitric acid
Nitrate formation
on the surface
N 2 O 5(g) + H 2 O (ads) → 2HNO 3(g)
S − OH + HNO 3(ads) → S − NO 3 + H 2 O (ads,g)

19. N 2 O 5(ads)
2HNO3(g)
+
Fresh CaCO3
H 2 O (ads) Adsorbed water
H2O
Aged CaCO3

20. Ozone reactivity on mineral dust: reaction or
decomposition?
Ozone
Decomposition: CaCO3
O 3 + SS → O(SS) + O 2
O 2 + O( 3 P) → O 3
O 3 + O(SS) → O 2 + O 2 (SS)
O 2 (SS) → O 2 + SS
net
2O 3 → 3O 2
Ozone
re-formation
r = 1.5
O 3 + SS → adduct
Reduction in of the Ozone
troposphere budget
O 3 + O(SS) → adduct
Ozone
Reactivity: Kaolinite, Saharan Dust;
Arizona Test Dust; natural limestone

21. Mineral dust and Atmospheric implications
Example of the N2O5 reactivity at T= 293K; lifetime increasing
cAγ
k het =
= 1/τ het (s −1 )
4
Loss rate constant due to heterogeneous uptake
of a gas species onto small particles (<2µ m)
A = 1.5 x 10-6 cm2 cm-3 (surface area density for Saharan Dust; c = mean
molecular speed; γ (NO3, N2O5) ~ 0.2
[NO2] = 10 ppb
loss ←O5 N 2 O 5

k N2
het
k
hydr
het
−4 −1
= 2.25x10 s
NO 2 + NO 3
k −1 [ NO 2 ] = 0.48s −1
NO
k het 3 = 2.4x10 −3 s −1
loss
HNO3
N2
k hetO5 = 2.0x10 −3 s −1
τ = 20s
k1 (293K) = 4.6x10 −2 s −1
NO
k ph 3 = 0.2s −1
−1
N
τ ss 2O5
NO
 N 2O5 k het 3 k1 (293) 
 = 8.5 min
=  k het +

k -1 [ NO 2 ] 


NO
τ het 3 = 7 min
NO
τ ph 3 = 5s

22. Soot production: incomplete fuel combustion
Flame Type
(Decane)
Rich
“gray”
40
Lean
Flame soot
Soot
type
“black”
20
3
Diameter soot
particle [nm]
Laboratory flame soot
Fuel: hexane,
octane, decane,
toluene, Diesel
 Black soot- low air/fuel ratios: soot highly agglomerated and consisted primarily of elemental C.
 Grey soot-high air/fuel ratios: soot less agglomerated and consisted of volatile organic materials.

23. N2O5 reaction on soot
0.7
N2O5 on 10 mg of grey soot
MS Signal (Volt)
0.6
reaction on (sample exposed)
plunger lowered
plunger lowered
0.5
N2O5
0.4
0.3
0.2
gas phase NO production
0.1
NOy
0.0
200
400
600
time (s)
800
1000
soot
renoxificatio
n
NOx = NO + NO2
0.7
MS Signal (Volt)
NOy
0.5
plunger lowered
reaction on (sample exposed)
plunger lowered
0.6
N2O5 on 10 mg of grey soot
N2O5
0.4
0.3
0.2
gas phase NO2 production
0.1
0.0
0
200
400
600
800
time (s)
1000
1200

24. Soot is a potential source of tropospheric HONO
NO 2 + soot(grey) → HONO + products
NO3 reaction on soot
NO + products
Heterogeneous reactions
(NO3 + NO2) reaction on soot (grey)
HONO formation

25. Heterogeneous interaction of trace gases on substrates of
technological importance: inkjet print paper
Samples: Polyester + AlOOH or SiO2 + Dye + additives
Fading effect
5 Torr NO2
1 Torr NO2

26. Acknowledgment
 M.J. Rossi
 Hubert Van den Bergh
 MINATROC project
 OFES foundation
 ILFORD Imaging GmbH (CH)
 Maria S.
 Cristina
 Flavio Comino
Thanks