TROPOSPHERIC CLEANSINGOXIDIZING CYCLES - PowerPoint PPT Presentation

Title: TROPOSPHERIC CLEANSINGOXIDIZING CYCLES


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TROPOSPHERIC CLEANSING/OXIDIZING CYCLES
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THE ATMOSPHERE OXIDIZING MEDIUM IN GLOBAL
BIOGEOCHEMICAL CYCLES
Oxidation
Oxidized gas/ aerosol
Reduced gas
Uptake
EARTH SURFACE
Emission
Reduction
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THE OH RADICAL MAIN TROPOSPHERIC OXIDANT
Primary source
O3 hn g O2 O(1D) (1) O(1D) M g O
M (2) O(1D) H2O g 2OH (3)
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TROPOSPHERIC OH PRODUCTION TAKES PLACEIN A
NARROW UV WINDOW (290-320 nm)
30o equinox midday Solar spectrum
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(No Transcript)
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THE OH RADICAL MAIN TROPOSPHERIC OXIDANT
TROPOSPHERIC HOx CYCLES
OH CO g H CO2 H O2 g HO2
(1) HO2 NO g OH
NO2 CH4 OH g CH3 H2O CH3 O2 g
CH3O CH3O2 NO g NO2 CH3O
(2) CH3O O2 g CH2O H2O CH2O OH, hv g
CO, OH, H2, HO2
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THE OH RADICAL MAIN TROPOSPHERIC OXIDANT
ATMOSPHERIC CLEANSING
CO OH g CO2 H CH4 OH g CH3 H2O HCFC,
VOC, Isop., OH NO2 OH g HNO3
Major OH sinks
g H2O
GLOBAL MEAN OH 1.0x106 molecules cm-3
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So what does all of this Tropospheric Oxidation
have to do with Climate Change?
Lets check with an old friend.
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IPCC AR4 SPM (2007)
Warming ?
? Cooling
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TROPOSPHERIC OZONE PRODUCTION DEPENDS ON NOx,
CO, CH4 AND OTHER ORGANIC COMPOUNDS
Take hydrocarbon RH
O3
HOxfamily cycle
NO
RO2
RO
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O2
RH
4
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PHOx
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O3
OH
HO2
NO
NO2
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HNO3
H2O2
O3
Catalytic Tropospheric O3 Production NO HO2/RO2
-gt NO2 followed by NO2 hv -gt NO O
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Present Day Budget Estimates For Tropospheric
Ozone tg O3
SOURCES 3400-5700 Chemical
production 3000-4600 HO2
NO (70)
CH3O2 NO (20)
RO2 NO (10)
Transport from stratosphere 400-1100 natural
ozone SINKS 3400-5700 Chemical
loss 2900-4200 O(1D)
H2O (40)
HO2 O3 (40)
OH O3 (10)
others (10)
Dry deposition 500-1500 MASS 300
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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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MAPPING OF TROPOSPHERIC NO2FROM THE GOME
SATELLITE INSTRUMENT (July 1996)
Martin et al. 2002
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LIGHTNING FLASHES SEEN FROM SPACE (2000)
DJF
JJA
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NEAR FUTURE 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
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IPPCs Optimistic A1B View of the More Distant
Future An Altenative View Grows to 75 TgN/yr by
2100
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Impacts of O3 precursor reductions on global
surface O3
Steady-state change in 8-hr daily maximum surface
O3 averaged over 3-month O3 season from 20
reductions in global anthropogenic emissions
NOx
NMVOC
CO
CH4
MOZART-2 model (2.8 x 2.8)
West et al., submitted
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Double dividend of methane controls Improved
air quality and reduced greenhouse warming
AIR QUALITY Change in population-weighted mean
8-hr daily max surface O3 in 3-month O3 season
(ppbv)
Steady-state results from MOZART-2
West et al.,submitted
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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
Ozone Climate forcing as sensitive to CH4 and NOx
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• Tropospheric Ozone Issues
• The Future Level is Uncertain
• Air Quality is focused on extreme values
• Climate forcing is driven by overall tropospheric
  column load
• Climate forcing is influenced at least as much by
  mid and upper tropospheric ozone
• Air Quality and Climate Change have the same
  general interest BUT

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GLOBAL BUDGET OF METHANE
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More than half of global methane emissions are
influenced by human activities 300 Tg CH4 yr-1
Anthropogenic EDGAR 3.2 Fast-Track 2000 Olivier
et al., 2005 200 Tg CH4 yr-1 Biogenic sources
Wang et al., 2004
BIOMASS BURNING BIOFUEL 30
ANIMALS 90
WETLANDS 180
LANDFILLS WASTEWATER 50
GLOBAL METHANE SOURCES (Tg CH4 yr-1)
GAS OIL 60
COAL 30
TERMITES 20
RICE 40
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Estimates for Changing Methane Sources in the
1990s
Biogenic adjusted to maintain constant total
source
547
Tg CH4 yr-1
BASE
EDGAR anthropogenic inventory
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GLOBAL DISTRIBUTION OF METHANENOAA/CMDL surface
air measurements
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HISTORICAL TRENDS IN METHANE
Recent methane trend
Historical methane trend
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RECENT TREND IN METHANE
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Observed trend in surface CH4 (ppb) 1990-2004
Global Mean CH4 (ppb)
Hypotheses for leveling off discussed in the
literature 1. Approach to steady-state 2.
Source Changes Anthropogenic Wetlands/pl
ants (Biomass burning) 3. (Transport) 4. Sink
(CH4OH) Humidity Temperature
OH precursor emissions overhead
O3 columns
NOAA GMD Network
Data from 42 GMD stations with 8-yr minimum
record is area-weighted, after averaging in bands
60-90N, 30-60N, 0-30N, 0-30S, 30-90S
Can the model capture the observed trend (and be
used for attribution)?
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A WIN-WIN CASE Methane emission controls
improve air quality and climate
Cost-saving reductions
Decrease in global ozone smog
0.5 ppbv
Cost-effective reductions (lt10/ton CO2 eq.)
1.0 ppbv
All identified reductions
1.5 ppbv
Decrease in global anthropogenic methane emissions
Proposed EPA rule costs 1 billion yr-1 to
reduce U.S. ozone by 1 ppb Cost-effective
reductions avoid 370,000 global premature
mortalities over 20 years decrease climate
forcing avoid other damages to health,
agriculture, forests, valued at 5 billion
West Fiore, 2005 West et al., 2006
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Double dividend of methane controls Improved
air quality and reduced greenhouse warming
AIR QUALITY Change in population-weighted mean
8-hr daily max surface O3 in 3-month O3 season
(ppbv)
Steady-state results from MOZART-2
West et al.,submitted
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CLASSIC GENERAL EXAM QUESTIONS
1. Loss of NOx in the troposphere takes place by
NO2OH, same as in the stratosphere. What is the
effect of this reaction on tropospheric ozone. 2.
Another version of that question. Why does NOx
destroy stratospheric ozone and produce
tropospheric ozone? 3. How might global warming
affect the source of OH in the troposphere? 4.
What would be the feedbacks on global warming
or -?