Tropospheric ozone and nitrogen oxides
Transport from the
Stratosphere: 475 Tg/yr
Chem prod in trop:
4920 Tg/yr
Chem loss:
4230 Tg/yr
Deposition: 1165 Tg/yr
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Global budget of tropospheric ozone
O3 is supplied to the troposphere by transport from stratosphere
Local production of O3 by reactions of peroxy radicals with NO:
HO2 + NO OH + NO2 [R1]
CH3O2 + NO CH3O + NO2 [R2]
RO2 + NO RO + NO2 [R3]
followed by photolysis of NO2
NO2 + h NO + O
O + O2 + M O3+ M
P(O3) = (k1 [HO2]+k2 [CH3O2]+k3 [RO2])[NO]
Loss of O3 by dry deposition (reaction with organic material at
the earths surface) and photochemical reactions:
[O3 + h O2 + O(1D)]
O(1D) + H2O OH + OH [R4]
HO2 + O3 OH + 2 O2 [R5]
OH + O3 HO2 + O2 [R6]
L(O3) = k4 [H2O][O(1D)] +k5 [HO2][O3]+k6 [OH][O3] + Ldeposition
Tropospheric O3 Budget
Jacob, Introduction to Atmospheric Chemistry
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Role of NOx in O3 production
Too little NOx: O3 loss (HO2+O3, OH+O3) rather than
radical cycling (e.g. HO2+NO) leading to net O3
chemical destruction.
P(O3)<L(O3) (NOx a few pptv. Marine troposphere)
Intermediate NOx: efficient O3 production via cycling
of HOx and NOx radicals.
P(O3)>L(O3) (Global free troposphere), P(O3) as NOx
Too much NOx: Radical termination by alternate
route (e.g. OH+NO2).
P(O3) decreases with increases in NOx
(NOx> a few hundred pptv, urban and rural atmosphere)
NOx and O3 production in the planetary boundary layer
(PBL) and in the upper troposphere (UT)
HO2 (PBL)
HO2 (UT)
OH (PBL)
OH (UT)
Net ozone production:
P(O3)-L(O3)
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Seasonal climatology of tropospheric ozone seen by satellite
DJF 1979-2000 MAM 1979-2000
JJA 1979-2000 SON 1979-2000
Tropospheric
O3 column (DU)
Fishman et al., Atmos. Chem. Phys., 3, 2003
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Climatological annual cycle of O3 for 22.5oN to 75oN
Logan, J. A., J. Geophys. Res., 104, 16115-16149, 1999
Global sources of nitrogen oxides (NOx)
Sources in TgN/year
Lightning Natural
Anthropogenic
0.4-0.8 2-10
Aircraft NOx
minutes
NO NO2
3-11 Loss (~hours)
HNO3
20-24 3-13
1-2 1-3
N-Fertilizers
Fossil fuel Biomass Soils
+ biofuel burning
Anthropogenic activity 3-6 fold increase in NOx emissions
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Distribution of surface NOx emissions
Lightning flashes seen from space
Jun-Jul-Aug 1999
Dec-Jan-Feb 1999 NOx source
~3-6 TgN/yr
http://thunder.nsstc.nasa.gov/data/otdbrowse.html
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Chemistry of nitrogen oxides in the troposphere
Sources from fossil fuel combustion, biomass burning, soils, lightning
(emitted as NO)
Rapid cycling between NO and NO2:
NO + O3 NO2 + O2
NO2 + h (+O2) NO + O3
Sink by formation of HNO3, during daytime:
NO2 + OH + M HNO3 + M
at night:
NO2 + O3 NO3 + O2
NO3 + NO2 + M N2O5 + M
N2O5 + aerosol (+H2O) 2 HNO3
HNO3 scavenged by precipitation in the lower troposphere within a
few days (wet deposition). NO, NO2 and HNO3 taken up by plants
over continents (dry deposition). In the upper troposphere, HNO3 is
recycled back to NOx by photolysis or reaction with OH.
Lifetime of NOx: ~hours near the surface, but 1-2 weeks in upper
troposphere.
Lower
stratosphere Stratosphere Stratosphere
HNO4
HO2 h
NOx
Lightning HO2/O3 NO3 aerosols
NO NO2 N2O5 HNO3
h h
Aircraft
h
h OH CH3CO3 h
OH
HNO2 PAN NO3 aerosols,
clouds
Surface Emissions
(Fossil Fuels, Biomass burning, Soils)
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NOx chemical lifetime (in days)
[1] NO + O3 NO2 + O2
[2] NO2 + hv NO + O
[3] NO2 + OH + M HNO3 + M
NOx = [NOx]/(k3[NO2][OH])
winter
=(1 + [NO]/[NO2])/k3[OH]
with [NO]/[NO2] = J2/(k1[O3])
In UT k1 ~5 times smaller than in BL
[k1 = 2 10-12 exp(-1400/T) molec/cm3/s]
And OH much smaller in UT than in BL
summer longer lifetime of NOx in the UT.
Levy II, H., et al., J. Geophys. Res., 104,
26279-26306, 1999
Mapping of Tropospheric NO2 columns from space: 2000
GOME GEOS-CHEM FIRE (VIRS/ATSR)
JANUARY
APRIL
JUNE
AUGUST
Jaegl et al. [2005]
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Long range transport of
anthropogenic NOx: formation of PAN
Peroxyacetyl nitrate (PAN, CH3C(O)OONO2) is produced by
photooxidation of hydrocarbons in the presence of NOx. Case of
acetaldehyde (CH3CHO):
CH3CHO+OH CH3CO+H2O
CH3CO+O2+M CH3C(O)OO+M
CH3C(O)OO+NO2+M PAN+M
PAN not soluble in water and is not removed by deposition.
Main loss by thermal decomposition:
PAN (+heat) CH3C(O)OO + NO2
Strong dependence of PAN decomposition on temperature:
PAN(295 K)~1 hour, PAN(250 K)~1-2 months
in the middle and upper troposphere PAN can be transported
over long distances and decompose to release NOx far from its
source.
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Global distribution of NOx (model-calculated) at the surface and at 5 km altitude
January July
Surface
5 km
Global distribution of HNO3 (model-calculated) at the surface and at 5 km altitude
January July
Surface
5 km
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Global distribution of PAN (model-calculated) at the surface and at 5 km altitude
January July
Surface
5 km
Sources of O3 precursors
Contribution from ~ 70% ~ 85% ~ 20% ~ 70%
anthropogenic sources
WMO, Scientific Assessment of Ozone Depletion, 1998
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Change in tropospheric ozone since pre-
industrial era
O3 is reactive: no ice core record.
Surface measurements in 19th and early 20th century
in Europe: much lower O3 (10-20 ppbv) than today
(40-50 ppbv), and different seasonal cycle. But
relationship to Northern Hemisphere concentrations
not obvious.
Global chemical transport models imply a 50%
increase in Northern Hemisphere O3 since pre-
industrial era due to increases in emissions of NOx,
CO, CH4 and hydrocarbons.
Ozone observations at the Montsouris
Observatory (outside Paris)
Voltz and Kley, 1988. Anfossi et al., 1991.
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Ozone observations at the Pic du Midi
(3000 m altitude, France)
Increase is important from
Marenco et al., JGR, 16617- pollution and climate perspectives
16632, 1994.
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