O3
hν
O(1D)
H2O
OH
O3
HO2
HO2
H2 O 2
Air Pollution Control and Air Chemistry:
The atmospheric oxidation capacity
(6th lecture)
Detlev Möller
Chair for Atmospheric Chemistry and Air Pollution Control
Faculty of Environmental Sciences and Process Engineering
Brandenburg Technical University Cottbus, Germany
Objectives:
To describe the atmospheric chemical OxHy system being an redox
cycle with the tendency to oxidize reduced trace substances such as
sulphur, nitrogen and carbon.
¾ oxidants and OxHy redox cycle,
¾ ozone chemistry and radical formation,
¾ oxidative stress
¾ summer smog, ozone dynamic
What does mean
oxidation (or oxidising) capacity or potential?
It is the ability of the atmosphere to oxidize trace substances.
Most trace substances (emission) are entering the atmosphere in
reduced from:
Sulphur(-II)
Sulphur (IV)
Nitrogen(-III)
Nitrogen(I)
Nitrogen(II)
Carbon(-IV)
Carbon(II)
H2S, DMS
SO2
NH3
N2 O
NO
CH4, NMVOC (RCH3)
CO
→ Sulphur(IV)
→ Sulphur(VI)
→ Nitrogen(II)
→ Nitrogen(II)
→ Nitrogen(V)
→ Carbon(II)
→ Carbon(IV)
oxidation process
SO2
SO42NO
NO
HNO3
CO
CO2
Each oxidation step is combined with a reduction (redox process).
In the atmosphere, most important oxidants are OxHx species
establishing the redox cycles between water (H2O) and oxygen (O2)
via active intermediates (radicals and peroxides).
There is no general (mathematical) definition. Often it is idenfied with
the OH radical concentration. We can not define it similar to the
redox potential in aqueous solutions.
From kinetic point of view, Xired + OXj → + Products, we can
ox
design it as the free reaction energy (Gibb´s potential): Ptherm = ∑ Δ R G j
j
ox
and as the specific oxidation potential (rate): Pkin =
∑k
j
j
⎡⎣OX j ⎤⎦
All important HxOy components
redox species
formation/destruction
name
H2O-
H2O + e-
aquated electron
H2O
OH + H / OH- + H+
water
level
-3
-2
-1
-1/±0
±0
H+(H3O+) -
hydrogen ion (hydrogenium)
OH-
OH + e-
hydroxyl ion
[O2-]
O2 + e-
oxide
H2O+
H2O – e- / OH + H+
water anion
OH
O + H / H2O - H
hydroxyl radical
HO2-
HO2 + e-
hydroperoxide anion
H2O2
OH + OH
hydrogenperoxide
O2-
O2 + e-
hyperoxide anion
HO2
O2 + H / O + OH
hydroperoxoradical
O3-
O3 + e-
ozonide anion
HO3
OH + O2
ozonide
HO4-
O3 + OH-
ozone acid anion (hypothetical)
H2O4
HO2 + HO2 / 2 OH + O2 ozone acid (hypothetical)
H
-
hydrogen
O
-
oxygen, atomar
O2
O+O
oxygen, molecular
O3
O + O2
ozone
redox states of oxygen species
eO3-
O3
H+
eH2O
H2O+
H+
HO3
OH-
H+
e-
OH-
OH
H+
O2-
H+
H2O2-
e-
H2O2
H2O4
H+
HO2
hν
H+
H+
e-
-2/-1
O
HO2
e-
HO2-
-2
O2
HO4-
e-
O22-
O2-
O2
-1/-1
-1/0
0
basic HxOy reactions in aqueous phase
catalase
Fenton reaction
dismutase
enzymatic reduction
desactivation
ozone decay
2 H2O2 → 2 H2O + O2
H2O2 (+ FeII) → OH + OH- (+FeIII)
HO2 + O2- (+ H+) → H2O2 + O2
O2 (+ e-) → O2O2- (+ FeIII) → O2 (+ FeII)
O3 + O2- (+ H+) → OH + 2 O2
Atmospheric chemistry
Ozone formation within the troposphere
O(3P) + O2 → O3
O3 + hν (λ<850 nm → O(3P) + O2
NO2 + hν (λ<420 nm → O(3P) + NO
OH chemistry of the clean atmosphere
hν
O3
M
O(3P)
O2
hν
O(1D)
H2O
OH
O3
H2O2
HO2
O3
HO2
OH chemistry of the polluted atmosphere
NO
O3, HO2 (-OH)
hν
NO2
het
hν
(-NO)
hν
(-NO)
O3
HNO2
NO
hν
OH
CO, VOC,
O3, SO2
RCHO
hν
NO2
HO2
HNO3
H2O2
HO2
RO2
ROOH
RONO2
NO2
RH
OH
O2
R
HO2
RO2
ROOH
NO (-NO2)
RO
(-CO2)
hν
O2 (-HO2)
RCHO
OH
RCR
hν (-HO2)
hν
O
RCO
O2
RC(O)O
NO (-NO2)
RC(O)OO
NO2
organic radical chemistry
RC(O)OONO2
[PAN]
The chemical cycle of
„reactive“ oxygen
O2
O2O
(ozone)
O(1D)
O(3P)
RC H
O+
O +H 2
OH
SO 3
CO 2
NO 2
NOO
NO
+ O2
SO 2 O
2
NO
CO + + 2 O 2 +
RC H 3
HOO
OH
[ NO] [ HO2 ]
k7
( 10 ppt)
k6
deposition
Catalytic ozone destruction
in remote areas
NO2
hν
formation on wetted surfaces
OH
HNO3
NO3
HNO2
nocturnal chemistry
O3
het
(precursors)
CO, VOC, SO2
OH
NO2
hν
O3
CO2, VOC´, SO3
(products)
O3
HO2
O3
urban ozone „titration“
NO
HO2
H2O2
O3
net:
CO + 2 O2 + hν → CO2 + O3
SO2 + 2 O2 + hν → SO3 + O3
RCH3 + 3 O2 + hν → RCHO + H2O + 2 O3
Dependence of ozone formation potential from NO and VOC concentration
(Sillman diagramme)
O3 formation potential (in ppb h-1)
VOC = 100 ppb C
VOC = 50 ppb C
VOC = 20 ppb C
10
9
8
7
6
5
4
3
2
1
0
0
5
10
NO concentration (in ppb)
15
20
gas phase
ozone formation cycle
NO
NO2
NO3
hv
H2O2
SO2
O3
HO2
H2O2
S(IV)
O3
HO2
S(VI) + products
aqueous phase
O2-
ORG
ORG
OH
OH
NO
HNO2
N(III)
N(V)
N2O5
NO3
ozone stoichiometry in sink products
1.5 O3
3.0 O3
2.0 O3
1.0 O3
0.5 O3
O3
PAN
NO
OH
HNO3
N2O5
NO2
NO3
hν
O3
0.5 O3
1.0 O3
VOC, CO
hν
hν
NO2
OH
HO2
HO2
H2O2
O3, HO2
NO
hν
hν
gas phase
OH
HNO2
liquid phase
NO3−
NO2−
OH
O3
VOC
S(IV)
H2O2
O2−/HO2
products
S(IV)
Oxidative stress
The scheme of atmospheric impact factors
climate forcing:
positive / negative
toxicity:
nutrient / pollutant
physico-chemical
properties of the
atmosphere
oxidation capacity:
oxidation / reduction
acidity:
acid / alkaline
Oxidative Stress
Oxidative stress is imposed on cells as a result of one of three factors:
1)
2)
3)
an increase in oxidant generation,
a decrease in antioxidant protection, or
a failure to repair oxidative damage.
Cell damage is induced by reactive oxygen species (ROS). ROS are either free radicals,
reactive anions containing oxygen atoms, or molecules containing oxygen atoms that can
either produce free radicals or are chemically activated by them. Examples are hydroxyl
radical, superoxide, hydrogen peroxide, and peroxynitrite. The main source of ROS in vivo is
aerobic respiration, although ROS are also produced by peroxisomal β-oxidation of fatty
acids, microsomal cytochrome P450 metabolism of xenobiotic compounds, stimulation of
phagocytosis by pathogens or lipopolysaccharides, arginine metabolism, and tissue specific
enzymes. Under normal conditions, ROS are cleared from the cell by the action of superoxide
dismutase (SOD), catalase, or glutathione (GSH) peroxidase. The main damage to cells results
from the ROS-induced alteration of macromolecules such as polyunsaturated fatty acids in
membrane lipids, essential proteins, and DNA. Additionally, oxidative stress and ROS have
been implicated in disease states, such as Alzheimer's disease, Parkinson's disease, cancer, and
aging.
Atmospheric oxidative stress precursers
atmosphere
cell
H2 O2
HO2 / O2-, OH
NO + O3
NO3
NO2 + O3
NO3
O3
OH
Ozone trend
European ozone trend
60
60
Pic
m) m)
Picdu
duMidi
Midi(3000
(3000
trend (without Arosa and Zugspitze)
Jungfraujoch
m) m)
Jungfraujoch(3500
(3500
O3 concentration (in ppb)
50
50
Mont
(1900
m) m)
MontVentoux
Ventoux
(1900
Deutsche
m) m)
DeutscheAlpen
Alpen(1046
(1046
40
40
Hoher Peißenberg(1000
(1000
Hohenpeissenberg
m) m)
Zugspitze(3000
(3000
Zugspitze
m) m)
30
30
Arosa(1860
(1860
Arosa
m)m)
20
20
10
10
00
1885
1885
1905
1905
1925
1925
1945
1945
year
1965
1965
1985
1985
2005
Ozone dependence from altitude
(after historic Soviet and Swiss data from the 1920s and 1930s)
16000
16
14000
14
y = 0,1083x 3,0499
R2 = 0,9965
altitude (in km)
12000
12
10000
10
8000
8
6
6000
4
4000
2
2000
00
00
10
10
20
30
30
40
40
50
O3 concentration (in ppb)
(note: in 2000-3000 m altitude about 15-20 ppb O3 must be added to the ground level)
Ozone trend at the station Wahnsdorf (near Dresden)
70
70
60
60
50
50
40
40
1995
year
[O3] = 35 + 1.4 x (1974-2000), r2 = 0.82
2000
1990
1997
1985
1994
1985
1980
1982
1975
1979
1976
1970
1973
1970
1965
1967
1955 1960
1964
1961
1958
00
1955
10
10
1991
20
20
1988
1974-2001
1974 – 2001
1971 – 1977
1972-1977
1960 – 1971
1960-1971
1955 - 1959
1955-1959
30
30
1952
O3 concentration (in µg m-3)
80
80
2000
European ozone trend (Marenco curve)
6060
Pic
(3000
m) m)
PicduduMidi
Midi
(3000
trend (without Arosa and Zugspitze)
Jungfraujoch
(3500
m) m)
Jungfraujoch
(3500
5050
Mont
(1900
m) m)
MontVentoux
Ventoux
(1900
O3 concentration (in ppb)
Deutsche
Alpen
(1046
m) m)
Deutsche
Alpen
(1046
4040
Hohenpeissenberg
(1000
m) m)
Hoher Peißenberg
(1000
Zugspitze
(3000
m) m)
Zugspitze
(3000
3030
Arosa
m) m)
Arosa(1860
(1860
altitude corrected Wahnsdorf data (3000 m)
altitude corrected Arosa data (3000 m)
2020
1010
00
1885
1885
1905
1905
1925
1925
1945
1945
year
1965
1965
1985
1985
Number of days with exceedance found at least at one station and annual
means from all stations in Germany (number of stations: 1990: 201 und
1999: 368); after Beilke 2000
90
>180 µg/m3
>240 µg/m3
annual mean
number of days and 80
[O3], resp. in µg/m3
70
60
50
40
30
20
10
19
99
19
98
19
97
19
96
19
95
19
94
19
93
19
92
19
91
19
90
0
24
28
16
24
ozone at 21 km (- 15%)
8
20
0
16
-8
12
-16
8
-24
4
-32
0
ozone at 5,5 km (+ 30%)
-40
-4
-48
-8
1967
1972
1977
1982
year
1987
1992
1997
2002
tropospheric ozone:
deviation from mean in nbar
Stratospheric ozone:
deviation from mean in nbar
Ozone trend at station Hohenpeißenberg
seasonal maximum (summer) and
minimum ozone (winter)
140
ozone concentration (in µg m-3)
Schwarzwald-max
Wank-max
120
Brotjackriegel-max
100
Schauinsland-max
Wurmberg-max
80
Brocken-max
Schwarzwald-min
60
Wank-min
Brotjackriegel-min
40
Schauinsland-min
Wurmberg-min
20
Brocken-min
0
1992
1993
1994
year
1995
1996
Trend ozone saisonal mean (winter)
[O3] in µg/m3
80
Schwarzwald
60
Wank
Brotjackriegel
Schauinsland
Wurmberg
40
Brocken
20
1992
1993
1994
year
1995
1996
Ozone variation
Ozone profil measurements by BTU mobile lidar Elight M510
downtown Berlin (Alexanderplatz) during an intercomparison campaign
with aircraft measurements In 1998 (BERLIOZ experiment)
summer-winter ratio of ozone concnetration
Altitude and saisonal variation
6
Spessart
1992
Königstein
5
1993
1994
4
1995
Brocken
3
1996
Mittelwerte
Schauinsland
Fichtelberg
2
Potenziell (Mittelwerte)
Wank
Zugspitze
1
Schwarzwald
Hoher Peißenberg
0
0
500
1000
1500
Altitude a.s.l. (in m)
2000
2500
3000
Summer smog
smog = smoke + fog
It is a meteorological situation when the formation of ozone is
being an optimum: high pressure system in summer (sun shine
and increased temperatures), low wind, no change of air masses
over a few days
Note: the conditions are quite different from those for the winter smog
Summer smog measurement campaign 1994
concentration (in ppb)
concentration (in ppb)
Summer smog measurement campaign at Mt. Brocken
date (June 28 – July 8, 1993)
concentration (in ppb)
Summer smog measurement campaign at Harzgerode
date (June 28 – July 8, 1993)
date (June 30 – July 8, 1994)
Mt. Brocken station
Harzgerode
Görendorf
0
data / time [UTC]
07/23/98 00:00
20:00
16:00
12:00
08:00
04:00
07/22/98 00:00
20:00
16:00
12:00
08:00
04:00
07/21/99 00:00
20:00
16:00
12:00
08:00
04:00
07/20/98 00:00
100
20:00
110
16:00
12:00
08:00
04:00
07/19/98 00:00
O3 cncentration (in ppb)
BERLIOZ measurement campaign 1998
120
Station Eichstädt near Berlin
Station Brocken/Harz
90
80
70
60
50
40
30
20
10
The ozone problem
natural sources
formation
potential
pollutants
destruction
potential
stratosphere
O3
deposition
anthropogenic sources
abatement
yes ?
impact
precursers
intermediates
org. N compounds
NO
O3
RH
harmful products
OH
HO2
hydrogen peroxide
org. peroxides &
carbonyl compounds
„photosmog“ – amplifying of toxicicity
Mean European Ozone
Winter ≈ 26 ppb
Summer ≈ 38 ppb
Stratospheric Ozone 10±3 ppb
Background Ozone 32±2 ppb
Biogenic Ozone 6±2 ppb
(seasonal variability 0-12 ppb)
Man-made non-NMHC Ozone 16±2 ppb
Hot Ozone
(man-made NMHC) 5 ppb
(seasonal variability 0-15 ppb
daily variability 0-70 ppb)
10-15% of mean ozone
40-50% of mean ozone
Contributions to the mean ozone concentration:
u
• 10 ppb natural background (photochem. and stratospheric)
• 20-25 photochemical from anthropogenic CH4 and CO (regional
man-made background)
• 30-35 ppb “basic contribution”
• the excess concentration > 30-35 ppb is given from NMVOC (“hot
ozone”)
v
• concentrations > 60 ppb may be observed only during
“summersmog“ situations
• since 1998 at no German station have been measured ocone with >
90 ppb
• the “basic concentration” of 30-35 ppb is globaly increasing
ozone abatement
• Global models are showing that the ozone concentration will be reduced by only 15% when
[NMVOC] = 0
• NMVOC are caused by 50-60% from traffic. 1/3 of the emission is originated during cold
start, i.e., a catalytic converter with 100% efficiency may reduce only 2/3 of total NMVOC
• Introduction of catalytical converters among the car fleet did reduce significant the number of
episodes with ozone exceedance (summersmog periodes)
• Essential is the reduction of NMHC with τOH < 3 d (high ozone formation potential).
• The reduction of CO by using catalytic converters did not show any effect on the mean ozone
concentration.
• “Key” for a reduction of the mean O3 concentration seems the limitation of CH4 emisisons
• Hence, the „mean ozone problem“ is linked with the “greenhouse problem” and the
problem “food for an increasing world population”.
[
The problem of further increasing mean ozone concentrations can be
solved only on global scale and not in a short-term approach.