Sensitivity of Surface Ozone to Nitrogen Oxides and Volatile Organic Compounds

1
Sensitivity of Surface Ozone to Nitrogen Oxides
andVolatile Organic Compounds

Arlene Fiore
Randall Martin Aaron Van Donkelaar
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Surface Ozone Remains a Major Issue Half of All
Canadians and Half of All Americans Live In
Regions that Fail to Achieve their Ozone Air
Quality Standards(Ozone impairs respiration,
reduces crop yields, oxidizes materials)
Observed Peak Surface Ozone Concentration For a
Typical Episode
1-hour Average Peak Concentration 1-hour Average Peak Concentration
           0-60 ppb
           61-79 ppb
           80-99 ppb
           100-110 ppb
           111-124 ppb
           125 ppb
3
Surface Ozone is Highly Sensitive to Climate
ChangeOzone-Temperature Relationship Observed
over 1980-1998
Probability of max 8-h O3 gt 84 ppbv vs. daily
max. T
1988, hottest on record!
Lin et al. Atm. Env. 2001
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Tropospheric Ozone

• Primary constituent of smog
• Major greenhouse gas
• Largely controls atmospheric oxidation

Global Budget of Tropospheric Ozone
Global sources and sinks, Tg O3 yr-1 (GEOS-CHEM
model)
Chem prod in troposphere 4900 Chem loss in troposphere 4200
Transport from stratosphere 500 Deposition 1200
?
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Simplified Tropospheric Ozone (O3) Chemistry
hv
OH
HNO3
NO
NO2
NOx
O3
HO2
OH
H2O2
HOx
hv, H2O
CO, VOCs
CO, VOCs, NOx
VOCs OH ? HCHO HCHO h? ? 2HO2 CO HCHO
OH ? HO2 CO H2O
Role of Formaldehyde (HCHO)
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Insignificant Trend (1980-1995) in Observed
Summer Afternoon Ozone Over Most of the United
States despite 12 decrease in VOC emissions (no
change in NOx emissions)Decreasing trend in
major metropolitan centers
Fiore et al., JGR, 1998
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Dependence of Ozone Production on NOx and VOCs
O3
HOx family OH HO2 RO RO2
NO
HCHO
RO2
RO
2
VOC
O2
1
3
PHOx
4
O3
OH
HO2
NO
NO2
6
5
HNO3
H2O2
O3
NOx- saturated or VOC-limited regime
NOx-limited regime
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Ozone Control Strategies Require Independent
Information on Effectiveness of Reducing NOx or
VOCs
Sillman introduced the concept of NOx-VOC
indicators, i.e. H2O2/HNO3 and HCHO/NOy (NOy
total reactive nitrogen)
NOx-saturated
NOx-limited
HCHO strongly correlated with HOx source VOC
oxidation
Predicted reduction in peak (afternoon) ozone for
a 35 decrease in NOx and VOC emissions
VOC
Sillman, JGR, 1995

• Would like to observe this transition from space
• Can observe tropospheric NO2 and HCHO columns . .
  .

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Diagnose Indicators with GEOS-CHEM Model

• Assimilated Meteorology (GEOS)
• 4ox5o horizontal resolution, 20 layers in
  vertical
• O3-NOx-VOC chemistry
• Radiative and chemical effects of aerosols
• Anthropogenic and natural emissions
• Cross-tropopause transport
• Deposition

Bey et al., JGR, 1999 Martin et al., JGR, 2002a
Calculated Mean Surface Ozone for August 1997
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Conduct Three Simulations

• Base Case
• Reduce Anthropogenic NOx Emissions by 50
• Reduce Anthropogenic VOC Emissions by 50

Fiore et al., JGR, 2002
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Tropospheric HCHO/NO2 Column Ratio Is an
Indicator of the Sensitivity of Afternoon Surface
Ozone to NOx and VOC EmissionsGEOS-CHEM Model
Calculation For Polluted Regions, Mar-Nov
NOx Saturated
NOx Titration
NOx Limited
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Tropospheric NO2 and HCHO Columns Largely
Confined Near the SurfaceAlso Closely Related to
NOx and VOC Emissions
Tropospheric NO2 column ENOx Tropospheric HCHO
column EVOC
Boundary Layer
CO
NO2
NO
HCHO
hours
NO/NO2 ? ? W ALTITUDE
OH
HO2
hours
VOC
hours
HNO3
Emission
Emission
Nitrogen Oxides (NOx)
Volatile Organic Compounds (VOC)
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Surface ozone concentrations are sensitive to the
ratio of NOx emissions to VOC emissions
(ppbv)
Sillman and He, 2002
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Retrieve Tropospheric NO2 and HCHO From the GOME
Satellite Instrument

• Operational since 1995
• Nadir-viewing solar backscatter instrument
  (237-794 nm)
• Low-elevation polar sun-synchronous orbit, 1030
  a.m. observation time
• Spatial resolution 320x40 km2, three cross-track
  scenes
• Complete global coverage in 3 days

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Perform a Spectral Fit of Solar Backscatter
Observations
absorption
Solar Io
l1
l2
Backscattered intensity IB
wavelength
Slant optical depth
Slant column
Scattering by Earth surface and by atmosphere
EARTH SURFACE
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Perform a Radiative Transfer Calculation to
Account for Viewing Geometry and
ScatteringRemove Scenes with IB,c gt IB,o
IB,c
IB,o
q

• LIDORT Radiative Transfer Model Spurr et al.,
  2002
• GOME Clouds Fields Kurosu et al., 1999
• GOME Surface Reflectivity Koelemeijer et al.,
  2001

Rc
Ro
Pc
t
Rs
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HCHO Columns Retrieved from GOME (July 1996)
2.5x1016 molecules cm-2
2
1.5
1
detection limit
0.5
South Atlantic Anomaly (disregard)
0
-0.5
High HCHO regions reflect VOC emissions from
fires, biosphere, human activity
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Tropospheric NO2 Columns Retrieved from GOME
(July 1996)
6x1015 molecules cm-2
4
2
detection limit
0
Martin et al., 2002b
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GOME Observations Generally Consistent With
In Situ Measurements from Aircraft
Houston Area
Houston Area
Latitude (degrees)
Tennessee
In Situ NO2 Measurements by Tom Ryerson In Situ
HCHO Measurements by Alan Fried
Latitude (degrees)
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GOME Observations Show NOx-Limited Conditions
Over Most Polluted Regions During AugustMajor
Industrial Areas are Clear Exceptions
White areas indicate clouds or data below the
GOME detection limit
August
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Dependence of Ozone Production on NOx and VOCs
O3
HOx family OH HO2 RO RO2
NO
HCHO
RO2
RO
2
VOC
O2
1
3
PHOx
4
O3
OH
HO2
NO
NO2
6
Lots of sunlight or little NOx
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Little sunlight or high NOx
HNO3
H2O2
O3
NOx- saturated or VOC-limited regime
NOx-limited regime
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Seasonal Evolution from NOx-Limited to
NOx-Saturated Conditions in Fall
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GOME Observations Provide Confidence in a Recent
Model Prediction NOx-Limited in the South and
NOx-Saturated in the North in Fall
GOME
Model
Luo et al., JGR, 2000
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Seasonal Maximum in Surface Ozone in Urban China
Occurs in Fall (More High-Pressure Systems)
In-situ Surface Ozone Measurements
Fall NOx-saturated conditions noteworthy
Luo et al., JGR, 2000
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Biomass Burning Emissions are Clearly
NOx-Limited, In Contrast with NOx-Saturated
Conditions Over the Industrial Highveld
Also observe plume evolution
August
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Present and Future Satellite Observations of
Tropospheric Composition
Platform multiple multiple ERS-2 Terra Terra ENVISAT ENVISAT Aura Aura Aura CloudSat TBD
Sensor TOMS AVHRR/SeaWIFS GOME MOPITT MODIS/MISR SCIAMACHY MIPAS TES OMI MLS CALIPSO OCO
Launch 1979 1995 1999 1999 2002 2002 2004 2004 2004 2004 2007
O3 N N/L L N/L N L
CO N N/L L N/L
CO2 N/L N
NO L
NO2 N N/L N
HNO3 L L
CH4 N/L N
HCHO N N/L N
SO2 N N/L N
BrO N N/L N
HCN L
aerosol N N N N N N
Increasing spatial resolution
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Conclusions

• Satellite remote-sensing of tropospheric NO2 and
  HCHO enables global characterization of
  ozone-NOx-VOC sensitivity
• Most of the world is NOx-limited, especially
  during summer
• NOx-saturated (VOC-limited) conditions occur
  under decreased sunlight or in major industrial
  centers