TROPOSPHERIC OZONE AND OXIDANT CHEMISTRY

1
TROPOSPHERIC OZONE AND OXIDANT CHEMISTRY
The many faces of atmospheric ozone
In stratosphere UV shield
Stratosphere 90 of total
In middle/upper troposphere greenhouse gas
Troposphere
In lower/middle troposphere precursor of OH,
main atmospheric oxidant
In surface air toxic to humans and vegetation
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OZONE CHEMISTRY IN STRATOSPHERE

• By contrast, in troposphere
• no photons lt 240 nm
• no oxygen photolysis
• neglible O atom conc.
• gno XO O loss

3
CONSTRAINT ON CROSS-TROPOPAUSE OZONE FLUXFROM
OBSERVED OZONE-NOy CORRELATION IN LOWER STRAT
NOy chemical family
Oxidation products (HNO3, etc.)
FN2O EN2O
tropopause
EN2O 13 Tg N yr-1 (17)
4
OZONE LOSS IN TROPOSPHERE
tropopause
Chemical loss
deposition
Ozone chemical loss is driven by photolysis
frequency J(O3 gO(1D)) at 300-320 nm
Closing the tropospheric ozone budget requires a
tropospheric chemical source gtgt FO3
dJ/dl, 10-6 s-1 nm-1
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OZONE PRODUCTION IN TROPOSPHERE
Photochemical oxidation of CO and volatile
organic compounds (VOCs) catalyzed by hydrogen
oxide radicals (HOx) in the presence of nitrogen
oxide radicals (NOx)
HOx H OH HO2 RO RO2 NOx NO NO2
OH can also add to double bonds of unsaturated
VOCs
Oxidation of VOC
Oxidation of CO
RO can also decompose or isomerize range of
carbonyl products
Carbonyl products can react with OH to produce
additional ozone, or photolyze to generate more
HOx radicals (branching reaction)
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General rules for atmospheric oxidation of
hydrocarbons

• Attack by OH is by H abstraction for saturated
  HCs, by addition for unsaturated HCs
• Reactivity increases with number of C-H bonds,
  number of unsaturated bonds
• Organic radicals other than peroxy react with O2
  (if they are small) or decompose (if they are
  large) O2 addition produces peroxy radicals.
• Organic peroxy radicals (RO2) react with NO and
  HO2 (dominant), other RO2 (minor) they also
  react with NO2 but the products decompose rapidly
  (except in the case of peroxyacyl radicals which
  produce peroxyacylnitrates or PANs)
• RO2HO2 produces organic hydroperoxides ROOH,
  RO2NO produces carbonyls (aldehydes RCHO and
  ketones RC(O)R) and also organic nitrates by a
  minor branch
• Carbonyls and hydroperoxides can photolyze
  (radical source) as well as react with OH
• Unsaturated HCs can also react with ozone,
  producing carbonyls and carboxylic acids
• RO2RO2 reactions produce a range of oxygenated
  organic compounds including carbonyls, carboxylic
  acids, alcohols, esters

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GLOBAL BUDGET OF TROPOSPHERIC OZONE (Tg O3 yr-1)
IPCC (2007) average of 12 models
O2
hn
O3
Ozone lifetime 24 4 days
STRATOSPHERE
8-18 km
TROPOSPHERE
hn
NO2
NO
O3
hn, H2O
OH
HO2
H2O2
Deposition
CO, VOC
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CARBON MONOXIDE IN ATMOSPHERE
Source incomplete combustion Sink oxidation by
OH (lifetime of 2 months)
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SATELLITE OBSERVATIONS OF BIOMASS FIRES (1997)
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SATELLITE OBSERVATION OF CARBON MONOXIDE
MOPITT CO columns (Mar-Apr 01)
11
ATMOSPHERIC SOUNDING IN THE THERMAL IR
Satellite measures
z
B(l,T(z))dt
dz
absorbing gas
B(l,To)
Measurement over a range of wavelengths with
different s(l,z) provides constraints on
retrieval of vertical profile n(z) problem is
generally underconstrained gmust solve the
inverse problem with Bayesian optimization
Lo
1
atmospheric transmittance L
12
GLOBAL METHANE SOURCES, Tg y-1 IPCC, 2007
BIOMASS BURNING 10-90
ANIMALS 80-90
WETLANDS 100-230
LANDFILLS 40-70
GAS 50-70
TERMITES 20-30
COAL 30-50
RICE 30-110
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GLOBAL DISTRIBUTION OF METHANENOAA/CMDL surface
air measurements
Sink oxidation by OH (lifetime of 10 years)
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SPACE-BASED METHANE COLUMN OBSERVATIONS
by solar backscatter at 2360-2385 nm
15
SPACE-BASED MEASUREMENTS OF ATMOSPHERIC COLUMNS
BY SOLAR BACKSCATTER
Examples TOMS, GOME, SCIAMACHY, MODIS, MISR,
OMI, OCO Applications to retrievals of O3, NO2,
HCHO, BrO, CO, CO2, aerosols
absorption
Backscattered intensity IB
l1
l2
wavelength
Slant optical depth
Scattering by Earth surface and by atmosphere
Slant column
Vertical column
The air mass factor (AMF) depends on viewing
geometry and radiative transfer
16
AIR MASS FACTOR (AMF) CONVERTS SLANT COLUMN WS
TO VERTICAL COLUMN W
Geometric AMF (AMFG) for non-scattering
atmosphere
EARTH SURFACE
17
IN SCATTERING ATMOSPHERE, AMF DEPENDS ON VERTICAL
DISTRIBUTION OF ABSORBER
340 nm
HCHO
EARTH SURFACE
Need additional information on the shape of the
vertical profile for any given scene this can
come from a model or from climatological
observations
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HISTORICAL TRENDS IN METHANE
The last 20 years
The last 1000 years
IPCC 2007
19
IPCC 2001 Projections of Future CH4 Emissions
(Tg CH4) to 2050
Scenarios
900
A1B A1T A1F1 A2 B1 B2 IS92a
800
700
600
2020
2040
2000
Year
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NON-METHANE VOC EMISSIONS
Alkanes, alkenes, aromatics
Isoprene, terpenes, oxygenates
Alkenes, aromatics, oxygenates
600 Tg C yr-1
200 Tg C yr-1
50 Tg C yr-1
Industry
Vegetation
Biomass burning
Largest global flux is from isoprene (300-500 Tg
C yr-1)
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Global Distribution of Isoprene Emissions
E f (T, h?)
MEGAN biogenic emission model (Guenther et al.,
2006)
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CONSTRAINT ON VOC EMISSIONS FROM SPACE
OBSERVATIONS OF FORMALDEHYDE
GOME satellite observations (July 1996)
2.5x1016 molecules cm-2
2
1.5
1
detection limit
0.5
South Atlantic Anomaly (disregard)
0
-0.5
High values are associated with biogenic
emissions (eastern US), anthropogenic emissions
(China), fires (Africa, Siberia)
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FORMALDEHYDE COLUMNS FROM OMI (Jun-Aug 2006)
high values are due to biogenic isoprene (main
reactive VOC)
GEOS-Chem model w/best prior (MEGAN) biogenic
VOC emissions
OMI
MEGAN emission hot spots not substantiated by the
OMI data
Millet et al. 2007
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NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE
STRATOSPHERE 0.2
LIGHTNING 5.8
SOILS 5.1
FOSSIL FUEL 23.1
BIOMASS BURNING 5.2
BIOFUEL 2.2
AIRCRAFT 0.5
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SATELLITE OBSERVATIONS OF TROPOSPHERIC NO2
SCIAMACHY data. May-Oct 2004 (R.V. Martin,
Dalhousie U.)
detection limit
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TROPOSPHERIC NO2 FROM THE OMI SATELLITE
INSTRUMENT (MARCH 2006)
March 2006
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LIGHTNING FLASHES SEEN FROM SPACE (2000)
DJF
JJA
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PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR
LONG-RANGE TRANSPORT OF NOx
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NOAA/ITCT-2K2 AIRCRAFT CAMPAIGN IN APRIL-MAY 2002
Monterey, CA
Asian pollution plumes transported to California
May 5 plume at 6 km High CO and PAN, no O3
enhancement
CO
PAN
O3
HNO3
NOx
PAN
May 17 subsiding plume at 2.5 km High CO and
O3, PAN gNOxgHNO3
O3
HNO3
CO
NOx
Hudman et al. 2004
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INTEX-B Aircraft Measured Transpacific Plume on
May 9th
GEOS-Chem CO at 680 hPa on May 9
A-north branch
Solid observations Dot GEOS-Chem
A
PAN
B
O3
CO
B-south branch
Simulated net ozone production at 680 hPa
PAN
A
B
O3
CO
NO
HNO3
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Ozone Production in Transpacific Plumes
L
H

• Direct transport of Asian ozone produced in the
  boundary layer and continuous ozone formation
  over the Pacific
• Splitting of transpacific plumes over the
  northeast Pacific

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Transport of Asian Ozone and its Precursors
The mean Asian ozone, CO, NOx, and PAN
enhancements at 800 hPa for INTEX-B
CO
Ozone
NOx
PAN
Latitudinal distribution of NO2 and PAN at 1.5 -5
km
NO2
PAN
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GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE
Climatology of observed ozone at 400 hPa in July
from ozonesondes and MOZAIC aircraft (circles)
and corresponding GEOS-Chem model results for
1997 (contours).
GEOS-Chem tropospheric ozone columns for July
1997.
Li et al., JGR 2001
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TES SATELLITE OBSERVATIONS IN MIDDLE TROPOSPHERE
(July 2005)
averaging kernels
Zhang et al. 2006
35
TES ozone and CO observations in July 2005 at 618
hPa
North America
Asia
TES observations of ozone-CO correlations test
GEOS-Chem simulation of ozone continental outflow


Zhang et al., 2006
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GEOS-Chem GLOBAL BUDGET OF TROPOSPHERIC OZONE
Present-day Preindustrial
O2
hn
O3
STRATOSPHERE
8-18 km
TROPOSPHERE
hn
NO2
NO
O3
hn, H2O
OH
HO2
H2O2
Deposition
CO, VOC
37
IPCC RADIATIVE FORCING ESTIMATE FOR TROPOSPHERIC
OZONE (0.35 W m-2) RELIES ON GLOBAL MODELS
but these underestimate the observed rise in
ozone over the 20th century
Preindustrial ozone models

Observations at mountain sites in Europe
Marenco et al., 1994
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RADIATIVE FORCING BY TROPOSPHERIC OZONE COULD BE
MUCH LARGER THAN IPCC VALUE
Global simulation of late 19th century ozone
observations Mickley et al., 2001
Standard model DF 0.44 W m-2 Adjusted
model (lightning and soil NOx decreased, biogenic
hydrocarbons increased) DF 0.80 W m-2
39
IPCC 2007
40
RECENT TRENDS IN TROPOSPHERIC OHinferred from
methylchloroform observations
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OZONE AND PARTICULATE MATTER (PM) THE TOP TWO
AIR POLLUTANTS IN THE U.S.
millions of people living in areas exceeding
national ambient air quality standards (NAAQS) in
2006
84 ppbv
15 mg m-3 (day), 65 (annual)
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U.S. CONTIES EXCEEDING THE OZONE AIR QUALITY
STANDARD (2003)
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OZONE CONCENTRATIONS vs. NOx AND VOC
EMISSIONSAir pollution model calculation for a
typical urban airshed
NOx-limited
Ridge
NOx- saturated
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LARGE SUPPLY OF BIOGENIC VOCs unrecognized
until the 1990s
Switches polluted areas in U.S. from
NOx-saturated to NOx-limited regime! recognized
in Revised Clean Air Act of 1999
Isoprene (biogenic VOC)
Anthropogenic VOCs
Jacob et al., J. Geophys. Res. 1993
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LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC
VOCs
notice difference in scale!
Millet et al. 2007
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U.S. ANTHROPOGENIC NOx AND VOC EMISSIONS (2003)
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OZONE TRENDS IN U.S. http//www.epa.gov/airtrends
/
National trend
Boston trend
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TREND IN 4th-HIGHEST 8-HOUR OZONE,1992-2001
EPA, 2003
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EVEN IN NOx-LIMITED REGIME,THE TOTAL O3 PRODUCED
IS VOC-DEPENDENTAND O3 f(ENOx) IS STRONGLY
NONLINEAR
P(O3)
L(NOx)
HO2,RO2,O3
OH, O3
NO
NO2
HNO3
hv
Emission
Deposition
Define ozone production efficiency (OPE) as the
total number of O3 molecules produced per unit
NOx emitted.
Assuming NOx steady state, efficient HOx cycling,
and loss of NO2 by reaction with OH
OPE m as NOx k e strong nonlinearity in models,
decreasing NOx emissions by 50 reduces ozone
only by 15
50
1999-2004 NOx EMISSION REDUCTIONSAND SIMULATED
EFFECTS ON SURFACE OZONE
50 decrease in power plant emissions 20
decrease in total U.S. emissions
Hudman et al. 2007
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TRENDS IN 4th-HIGHEST 8-HOUR OZONEAT NATIONAL
PARKS, 1992-2001 EPA, 2003
52
OBSERVED TREND IN OZONE BACKGROUND OVER
CALIFORNIA IN SPRING SUGGESTS 10-15 ppbv
INCREASEOVER PAST 20 YEARS
Trend 0.5-0.8 ppbv yr-1
Jaffe et al. 2003
Background concentration that would be present
in absence of local anthropogenic emissions
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RISING OZONE BACKGROUND IN EUROPE
Hohenpeissenberg/ Payerne
3-5 km
polluted
Naja et al. 2003
background
Changes in anthrop. NOx emissions
Mace Head, 1987-2004 Simmonds et al., 2004
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HEMISPHERIC OZONE POLLUTIONIMPLICATIONS OF
ENHANCED OZONE BACKGROUND FOR MEETING AIR
QUALITY STANDARDS (AQS)
Europe AQS (8-h avg.)
Europe AQS (seasonal)
U.S. AQS (8-h avg.)
U.S. AQS (1-h avg.)
0 20 40
60 80 100
120 ppbv
Preindustrial ozone background
Present-day ozone background at northern
midlatitudes
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GLOBAL OZONE BACKGROUNDMETHANE AND NOx ARE THE
LIMITING PRECURSORS
Sensitivity of global tropospheric ozone
inventory (Tg) to 50 global reductions In
anthropogenic precursor emissions
GEOS-Chem model Fiore et al., 2002
Anthropogenic methane enhances surface ozone by
4-6 ppbv worldwide
56
PROJECTIONS OF GLOBAL NOx EMISSIONS
Anthropogenic NOx emissions IPCC, 2001
2000
Optimistic IPCC scenario OECD, U.S. m20,
Asia k 50
2020
109 atoms N cm-2 s-1
57
EFFECT OF INCREASING SIBERIAN FOREST FIRES ON
SUMMER SURFACE OZONE IN PACIFIC NORTHWEST
GEOS-CHEM ozone enhancements
Observations
Siberian fires
CO
Ozone
Mean summer 2003 enhancement of 5-9 ppbv (9-17
ppbv in events)
Jaffe et al. 2004
58
EMEP/IPCC REPORT (Jan 05)
The future ozone level in Europe is closely
linked to global warming
Methane (and CO) emission control is an
effective way of simultaneously meeting air
quality standards and abating global warming
59
EFFECT OF CLIMATE CHANGE ON OZONE AIR QUALITY
Probability of max 8-h O3 gt 84 ppbv vs. daily
max. T
Ozone exceedances of 90 ppbv, summer 2003
Lin et al. Atm. Env. 2001

• Correlation of high ozone with temperature is
  driven by
• stagnation, (2) biogenic hydrocarbon emissions,
  (3) chemistry

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EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION
GISS GCM simulations for 2050 vs. present-day
climate using pollution tracers with constant
emissions
weather map illustrating cyclonic ventilation of
the eastern U.S.
2045-2052
summer
1995-2002
Pollution episodes double in duration in 2050
due to decreasing frequency of cyclones
ventilating the eastern U.S expected result of
greenhouse warming.
Mickley et al. GRL 2004