physik der atmosphäre ii u. platt ss 2009, tuesday, 16:15-17:45, inf 229, sr 108/110 31....
TRANSCRIPT
Physik der Atmosphäre IIU. Platt
SS 2009, Tuesday, 16:15-17:45, INF 229 , SR 108/110
31. 3. Introduction - Gas-Phase Reaction Kinetics Pl
7. 4. Tropospheric Chemistry: O3, HxOy, Oxidation Capacity Pl
14. 4. Tropospheric Chemistry: N-, S-, Halogen – Cycles Pl
28. 4. Stratosphere, Radiation and Matter Cycles Pl
5. 5. Strat. Chemistry: Chapman Cycle and Extensions Pl
12. 5. Strat. Chemistry: Halogen Chemistry, The Ozone Hole Pl
19. 5. Isotopes in Atmospheric Research Pl
26. 5. The Carbon Cycle Pl
2. 6. The Hydrological Cycle Pl
9. 6. Liquid Phase Chemistry (atmspheric Aerosol) Pl
16. 6. Aerosol Physics I: Aerosol Mechanics Pl
23. 6. Aerosol Physics II: Particle Formation, Particle Growth Pl
30. 6. Measurement Techniques Pl
7. 7. Modeling Atmospheric Chemistry and Physics Pl
Physics of the Atmosphere Physik der Atmosphäre
WS 2010
Ulrich PlattInstitut f. Umweltphysik
Last Week
• The carbon cycle has a strong influence on our climate(both, in natural changes and anthropogenic changes)
• Important carbon reservoisrs are the sediments, the ocean, the land biomass, and the atmosphere
• Time constants in the carbon cycle range from years to 105 years
• Oceans get more acidic less carbon uptake
• The role of the biomass is unclear
Contents
Ozone, Hydrogen Radicals (HXOY ), and the Oxidation Capacity
Examples: OH, HO2, as well as the "stable" Molecules
H2O2 (hydrogen peroxyde) and CH3OOH (methyl hydroperoxide).
1st Definition:Radicals are a combination of atoms that have one or several unpaired electrons. (i.e. S 0).This definition, however, includes O2, NO or NO2.
2nd Definition:Radicals are (short lived) combinations of atoms, which play the role of elements and can combine like these with elements and with themselfes.(Justus von Liebig)
First question: What are „Free Radicals“?
Why are Radicals important?Atmospheric mixing ratios of radicals are exceedingly low e.g. about 1 OH-radical for every 1013 air moleculesBut:In chemical reactions with molecules the radical status is „hereditary“ e.g.:OH + CO CO2 + H
Example: oxyhydrogen gas (Knallgas):
H2 + O2 HO2 + H „Start“
H2 + HO2 OH + H2O PropagationH2 + OH H + H2O (inherit radical status)
H + O2 OH + O BranchingO + H2 OH + H (from one radical we get two)
OH + HO2 H2O + O2 Termination
Net: 2 H2 + O2 2 H2O
Consequence: The radikal concentration and thus the speed of the reaction can increase exponentially.
Does that also happen in the atmosphere?
Free Radicals - Which ones are Important in Atmospheric Chemistry?First suggestion of OH reactions in the atmosphere by B. Weinstock 1969.Formation of OH by:
O3 + h O(1D) + O2(1)O(1D) + H2O OH + OH
Role of OH in the formation of CO and formaldehyde suggested [H. Levy 1971].Role of OH in tropospheric ozone formation (P. Crutzen 1974)
Other Radicals (by either definition)? O2(1), Cl-atoms, NO3 ...
HOX - Cycle
OH Degradation of most VOC Key intermediate in O3 formation
NOX NOY conversion
HO2
Intermediate in O3 formation
Intermediate in H2O2 formation
RO2
Intermediate in ROOR´ formation Aldehyd – precursor PAN – precursor Intermediate in O3 formation
XO Catalytic O3 destruction (X = Cl, Br, I)
Degradation of DMS (BrO) Particle formation (IO) Change of the Leighton – Ratio
X Degradation of most (some) VOC: Cl (Br) Initiates O3 formation
RO2 – precursor
NO3
Degradation of certain VOC NOX NOY conversion (via N2O5)
RO2 – precursor
Degaradation of Trace Species by Reaction with OH- or other Free Radicals.
Mean Lifetime in Hours against Radical Reaktions
Spezies OH
mittelw. OH
(peak) NO3 (av.)
NO3 (peak)
ClO (av.)
ClO (peak)
Cl (av.)
Cl (peak)
BrO (av.)
Br (av)
Typ. Konz. in Molek.
cm-3 6105 1107 1.5108 11010 106 108 103 105 108 5106
DMS 110a 6.3a 1.7a 0.03a 3104 c 280c 870f 8.7f 10c 26g
n-Butane 190a 11a 2.8104
a 430 a - 1400h 14h
C2H4 56b 3.4b 1104 h 160h 2800b 28b
Isoprene 4.6h 0.3h 1.9h 0.03h - <1100d <11d 0.9e
Toluene 77h 4.6h 3.1104
h 460h -
CH4 7104 a 4103 a >5104 h >700h >7107
b >7105
b 3106 a 3104 a
A X A,XA X
Degradation of species A by radical X :
1d kA X A tk Xdt
OH Formation in the Atmosphere
The most important source of OH-radicals is the photolysis of ozone by UV-radiation with wavelengths < ca. 320 nm (R1a) (UV-B region) or 411nm (R1b):
O3 + h O(1D) + O2(1) (R1a)
O3 + h O(1D) + O2 (3) (R1b)
O3 + h O(3P) + O2 (3) (R1c)
Reaction R1b ist spin forbidden, thus unlikely.
O (1D) + M O (3P) + M (R2)
O (1D) + H2O OH + OH (R3)
OH - yield:
3 2
32 22a 2b 2
k H OV
k k kN H OO
Photochemical OH - Formation
2
1
J I d
Photolysis Frequency:
Annual Variation of the Photochemical OH – Formation Rate at Mid-Latitudes
Month
OH
Rat
e of
For
mat
ion
cm-3s-1
The HXOY - Cycle
CH2O
HO2OH
NO2 NO
H2O2HNO3
HONO
OH(O2)
NO(O2)
CH3O2
O3(O2)
O3
h
O3
O3
CO(O2)
H2(O2)
CH2O(O2)
H2O
h,
OH
CH4(NMHC)
H2O
h(O2)OH(O2)
[HOX] P(OH) „Final“ OH Sink
„Primary“OH
Source
P(OH)
[HOX] P(OH)
CH3O2
(CnH2n+1-O2)
HCHO
O3
Olefins
O3
Diurnal Variation of the Various
OH – Sources in an Urban Region
(Berlin)(Alicke 2000)
103
104
105
106
107
103
104
105
106
107
103
104
105
106
107
103
104
105
106
107
time [GMT]
from J(O1D) J(HONO) VOC's + O
3
J(HCHOrad
)
OH
pro
duct
ion
[mol
ec./(
cm3 s)
]
00:00 04:00 08:00 12:00 16:00 20:00 24:00
00:00 04:00 08:00 12:00 16:00 20:00 24:00
21.7.1998
20.7.1998
00:00 04:00 08:00 12:00 16:00 20:00 24:00
Nitrous Acid (HONO)
H2O(g) H2O(ads)(a)
NO2(g) NO2(ads) (b)
H2O(ads) + NO2(ads) H2O.NO2(ads) (c)
NO2(ads) + H2O.NO2(ads) HNO3(ads) + HONO(g)(d)[ HNO3(ads) + HONO(g) 2 NO2(g) + H2O(g) ]
The OH – Cycle as Function of the NOX -
Concentration
[NO ] = 0X
86 %
14 %
O H
O H
4* 1 0 c m6 -3
96 %
+ HO 2 4 %H O
H O(Pe ro xid e )
(Pe ro xid e )
HO 2
2
2 2
[NO ] = 2 p p b
3
2
2
2
3
X20 %
80 %
se c
se c
O H
O H
14 * 10 c m6 -3
+ N O
H O
17 %
1 %
82 %
+ HO2
2
2
2 %
HN O 3
H O
2
H O 2
2
80 %
[NO ] = 100 p p bX
3 70 %
30 %
20 %C H O + h(+ O )
2
2
O H
3* 1 0 c m6 -3
se cO H
HO
2
90 % HN O 3
+ N O
2
10 %
+ C O+ KW
O + h+ H O
O + h+ H O
O + h+ H O
+ NO
+ NO
82%
+ O3
Model Calculations of the OH - Concentration as Function of the NOX (Oxides of Nitrogen) - Level
(D. Poppe)
Concentrations of OH and HO2 as a function of the NOX level
Conditions: 37.6 ppb ozone, 88.7 ppb CO, 0.92 ppb CH2O, J(O3)=9.110‑6 s‑1, J(NO2)=
9.110‑6 s‑1. The HO2 concentration and
therefore H2O2 production rate are highest in
unpolluted air at NOX levels below a few
100ppt. Figure from Ehhalt [1999]
Observed Diurnal Variation of the OH - Concentration
Red Circles: Measurements by Laser-Induced Fluorescence, LIF by A. Hofzumahaus et al., Jülich)
Blue, drawn Line: Ozone – Photolysis Frequency
BERLIOZ81% of OH dependent on J(O3)
0.0 1.0 2.0 3.0 4.0 5.0
0
2
4
6
8
10
12
14
J(O1D) / 10
-5 s
-1
[ O
H ]
/
1
06 cm
-3
NOX Dependence of OH -Observation
0.01 0.1 1 10 1000
2
4
6
8POPCORN 94
BERLIOZ 98
ALBATROSS 96
NOx / ppb
OH
/
106 c
m-3
Forschungszentrum
Jülich
OH (LIF) Summer & Winter
0.E+00
1.E+06
2.E+06
3.E+06
4.E+06
00:00 06:00 12:00 18:00 00:00
[OH
] / m
olec
ule
cm-3
0.0E+00
5.0E-06
1.0E-05
1.5E-05
2.0E-05
j(O1 D
) / s
-1
OH summer winter
j(O1D) summer winter
D.E.Heard, J.D.Lee, D.J. Creasey, University of LeedsL.J.Carpenter (University of York) c.f. George et al., 1999
Average ROX diurnal profile (Chemical Amplifier) during
BERLIOZ (July 14 to 15, 17 to 18, 24 to 26, Aug. 3, total of 8 days in 1998)
NO3 Data from Dieter Perner, in Platt et al. 2002
00:00 06:00 12:00 18:00 24:00
0
2
4
6
8
10
12
14
RO
2 [pp
t]
NoontimeRO2 Peak
NighttimeRO2 Peak:
NO3 + VOC
Radical Gap:no J(O3) but
still J(NO3)
HOX in the Upper Troposphere
Too much HOX ?
--> No, have to include other sources Photolysis of acetone, aldehydes, peroxides, ...
However, do these additional sources always explain observed HOX?
OH in the UT controlled by P(HOx) and NOx
Jaeglé et al., Atmos. Env. 2001
HOX Source Gases in the Free Troposphere(Pacific Ocean, spring 1999, Singh et al., Nature 2001)
SH,0-30oS, 165oE-100oW
NH,0-30oN, 170o-120oW
Nighttime Peroxy Radicals
0
2
4
6
8
10
12
14
0 3 6 9 12
Hour of night /GMT - 18 h
HO
2 +
RO 2
, N
O3 /p
ptv
0
5
10
15
20
25
30
35
40
45
O3 /p
pb
v
HO2 + RO2
NO3
O3
Salisbury et al. 2001
12:00 18:00 24:00 30:00 36:000
2
4
6
8
III
NO 3
[ppt]
0.0
0.2
0.4
0.6
0.8
1.0
II
J(NO3)
J(1OD)
arb
itra
ry u
nits [
s-1]
0
2
4
6
8
10
12
14
12:00 18:00 24:00 30:00 36:00
I
06:00 12:00
12:0006:00
RO
2 [p
pt]
NO3 Data from Dieter Perner, Platt et al. 2002
NO3 + olefins
O3 + olefins
Observed Diurnal Variations of OH-, HO2-,
RO2- and NOX- Concentrations During
BERLIOZ 1998 (Platt et al. 2002)
hohes NOX niedriges NOX
What is the Evidence for OH in theAtmosphere ?
What is the Evidence for HO2 (RO2) in the Atmosphere ?
Simplified Outline of the NOX- (=NO + NO2) and NOY- Cycles
N O 3 N O N O 2 E m is s io n R O 2
N 2 O 5
N 2 O
H N O 2 3NO
A e ro s o l
H N O 3
H O 2 N O 2 P A N
o x id a t io n s ta g e : 2 3 4 5 6
R O 2
< 1 0 % > 9 0 %
H 2 O liq .
H 2 O liq .
O H
O H
h
h h
O 3 O 3
N O , N O 2 , N O 3
?
V O C s
Temperature dependent!
Photolysis of the Nitrate Radical
The NO3 Spectrum Product Yield of NO3 Photolysis
NO3 Field Measurements
Cavity Ringdown(Boulder, CO)Brown et al. 2001 - Ravishankara
DOAS(Edwards AFB)Platt et al. 1984
NO3 Vertikal Profile - Schematic
z
NO2
NO3
NO, olefins
Low NO3 production(little NO3)
high NO3 destruction(lot of NO, terpenes)
1 km
0
Distance
Direction of Observation
SZA
OdenwaldMountains
Terminator
Institut für Umweltphysik
Z
NO3 - Vertical Profile Measurements
Geyer et al. 2001
Relative Importance of the Different NO3 - Loss Processes During BERLIOZ 1998
VOCsOOHNOfOOHNOVOCsdtd
oc 33 //33 ]//[:
- a ve ra g e o f a ll B E R LIO Z -d a ta- 2 4 h - m e a n va lu e s :
oc [cm -3s -1]N O 3 4 .51 0 5
O H 8 .11 0 5
O 3 2 .41 0 5
21
)()( 3
OHocNOoc
O H5 4 %
O 3
1 6 %
N O 3
3 0 %
Contribution of NO3 to the Atmospheric Oxidation Capacity in Pabstthum (BERLIOZ 1998)
Geyer et al. 2001
The Oxidation Capacity by Radical X
.]X][Y[k1i
iXYi
OC
Ozone Formation in the Troposphere
Initial Idea: Stratosphere
Troposphere
No Chemistry, since( 242 nm) = 0
O3 – Flux
5-81010
Molec.cm-2s-1
O3 – Depos.
3-61010
Molec.cm-2s-1
Stratosphere
Troposphere
CO, HC O3
O3 + h + H2O OH
O3 – Flux
5-81010
Molec.cm-2s-1
O3 – Depos.
3-61010
Molec.cm-2s-1
Today:
30-501010
Molec.cm-2s-1
Penetration-Depth of UV - Radiation
DeMore et al., 1997
Intensity at 0, 20, 30, 40, 50 km altitude)
NOX- and HOX - Katalysis of the Photochemical
Ozone Formation in the Troposphere
Ozone formation rate P(O3) :P(O3) = [NO]·(k1[HO2]+ki·[RO2]i)
Disturbance of the Leighton Ratio and the rate of O3 Formation
There is no net ozone production. However, if other reactions, in particular by Peroxy radicals oxidise NO to NO2:
RO2 + NO NO2 + RO (R4)
Ozone will be formed at the rate PO3. Also the Leighton Ratio will be reduced:
12 3 R 2
[NO] JL
[NO ] k [O ]+k [RO ]
O3 11 0
1 1P j NO
L L
The rate of ozone formation, PO3 in a given airmass can be calculated from
measurements of the Leighton Ratio [NO]/ [NO2]=L1 together with [O3], and J:
O3 R 2P k RO
Since PO3 relates to the concentration of peroxy radicals (RO2), there concentration can also be inferred from these measurements.
Smog Chamber Experiments Ozone IsopletsLines of constant O3 mixing ratios (ppb)
NOX-limited
Hydrocarbon-limited
Ozone Formation as a Function of NOX Level
Ehhalt 1998, Science 279. No. 5353, 1002 –
1003, DOI: 10.1126/science.279.5353.1002
Averaged O3 production rates PO3 calculated from simultaneous observations of NO, NO2, O3, OH, HO2,
H2CO, actinic flux, and T. Data were placed into three PHOx bins: high (0.5 < PHOx < 0.7 ppt/s, circles),
moderate (0.2 < PHOx < 0.3 ppt/s, squares), and low (0.03 < PHOx < 0.07 ppt/s, triangles), and then averaged as
a function of NO. All three PHOx regimes demonstrate the expected dependence on NO: PO3 increases linearly
with NO for low NO (<600 ppt NO), PO3 becomes independent of NO for high NO (>600 ppt NO). Crossover
between NOX - limited and NOX - saturated PO3 occurs at different levels of NO in the three PHOx regimes.
Observed O3 Production
Rates 'Southern Oxidant Study‘ June 15 to July 15, 1999 at Cornelia Fort Airpark,
Nashville, Tennessee [Thornton et al. 2002]
Diurnal variation of O3 levels in different air masses during August 11-14, 2000: Forrest (Weltzheimer Wald) and city of
Heilbronn (southern Germany).
Landesanstalt für Umweltschutz Baden-Württemberg and UMEG)
Vertical profiles of the concentrations of ozone, NO, H2O2, and humidity (dew point).
The maximum H2O2 concentration occurs in an altitude range layer (ca. 1.1 - 1.4 Km) with high humidity but low NO [Tremmel et al. 1993].
The Evolution of Tropospheric Ozone
Monks et al. 2009
Ozon – Annual Variation at Different Altitudes
Isobars 200, 300, 500, 800 hPa
Logan, J. Geophys. Res., 16115-16149, 1999.
Ozon – Annual Variation at Sea Level
Logan, J. Geophys. Res., 16115-16149, 1999.
Summary
•OH is the most important free radical in the Atmosphere, since it inititates the degradation of most oxidisable air pollutants it is sometimes called the „cleansing agent of the atmosphere“
•However, there are several other relevant Radical in the Atmosphere
•Ozone is a central species, in the troposphere it is mostly formed by reactions catalysed by OH