Upload
taya
View
24
Download
1
Tags:
Embed Size (px)
DESCRIPTION
THE ATMOSPHERE: OXIDIZING MEDIUM IN GLOBAL BIOGEOCHEMICAL CYCLES. Atmospheric oxidation is critical for removal of many pollutants, e.g. methane (major greenhouse gas) CO (toxic pollutant) HCFCs (Cl x sources in stratosphere). Oxidation. Oxidized gas/ aerosol. Reduced gas. Uptake. - PowerPoint PPT Presentation
Citation preview
THE ATMOSPHERE: OXIDIZING MEDIUM THE ATMOSPHERE: OXIDIZING MEDIUM IN GLOBAL BIOGEOCHEMICAL CYCLESIN GLOBAL BIOGEOCHEMICAL CYCLES
EARTHSURFACE
Emission
Reduced gasOxidized gas/aerosol
Oxidation
Uptake
Reduction
Atmospheric oxidation is critical for removal of many pollutants, e.g.• methane (major greenhouse gas)• CO (toxic pollutant)• HCFCs (Clx sources in stratosphere)
THE TROPOSPHERE WAS VIEWED AS THE TROPOSPHERE WAS VIEWED AS CHEMICALLY INERT UNTIL 1970CHEMICALLY INERT UNTIL 1970
• “The chemistry of the troposphere is mainly that of of a large number of atmospheric constituents and of their reactions with molecular oxygen…Methane and CO are chemically quite inert in the troposphere” [Cadle and Allen, Atmospheric Photochemistry, Science, 1970]
• Lifetime of CO estimated at 2.7 years (removal by soil) leads to concern about global CO pollution from increasing car emissions [Robbins and Robbins, Sources, Abundance, and Fate of Gaseous Atmospheric Pollutants, SRI report, 1967]
FIRST BREAKTHROUGH:
• Measurements of cosmogenic 14CO place a constraint of ~ 0.1 yr on the tropospheric lifetime of CO [Weinstock, Science, 1969]
SECOND BREAKTHROUGH:
• Tropospheric OH ~1x106 cm-3 predicted from O(1D)+H2O, results in tropospheric lifetimes of ~0.1 yr for CO and ~2 yr for CH4 [Levy, Science, 1971, J. Geophys. Res. 1973]
THIRD BREAKTHROUGH:
• Methylchlroform observations provide indirect evidence for OH at levels of 2-5x105 cm-3 [Singh, Geophys. Res. Lett. 1977]
…but direct measurements of tropospheric OH had to wait until the 1990s
WHY WAS TROPOSPHERIC OH SO DIFFICULT TO FIGURE OUT?WHY WAS TROPOSPHERIC OH SO DIFFICULT TO FIGURE OUT?
Production of O(Production of O(11D) in troposphere takes place in narrow band [290-320 nm]D) in troposphere takes place in narrow band [290-320 nm]
solar flux I
ozone absorptioncross-section
O(1D)quantumyield
I
~tropopause
10 ppmv
40 ppbv
TYPICAL OZONE PROFILE: ~10% OF OZONE COLUMN TYPICAL OZONE PROFILE: ~10% OF OZONE COLUMN GLOBALLY IS IN THE TROPOSPHEREGLOBALLY IS IN THE TROPOSPHERE
• Estimate ozone flux FO3 across tropopause (strat-trop exchange)
– Total O3 col = 5x1013 moles
– 10% of that is in troposphere
– Res. time of air in strat = 0.7 yr
• Estimate CH4 source SCH4:
– Mean concentration = 1.7 ppmv
– Lifetime = 9 years
• Estimate CO source SCO:
– Mean concentration = 100 ppbv
– Lifetime = 2 months
UNTIL ~1990, PREVAILING VIEW WAS THAT UNTIL ~1990, PREVAILING VIEW WAS THAT TROPOSPHERIC OZONE ORIGINATED MAINLY TROPOSPHERIC OZONE ORIGINATED MAINLY FROM STRATOSPHERE…but that cannot work.FROM STRATOSPHERE…but that cannot work.
FO3 = 3x1013 moles yr-1
SCH4 = 3x1013 moles yr-1
SCO = 8x1013moles yr-1
SCO+ SCH4 > 2FO3 OH would be titrated!
Recycling of OH involving NOx is critical, and this recycling drives tropospheric ozone production
RADICAL CYCLE CONTROLLING TROPOSPHERIC OH RADICAL CYCLE CONTROLLING TROPOSPHERIC OH AND OZONE CONCENTRATIONSAND OZONE CONCENTRATIONS
O3
O2 h
O3
OH HO2
h, H2O
Deposition
NO
H2O2
CO, CH4
NO2
h
STRATOSPHERE
TROPOSPHERE
8-18 km
SURFACE
GLOBAL BUDGET OF TROPOSPHERIC OZONE (MODEL)GLOBAL BUDGET OF TROPOSPHERIC OZONE (MODEL)
O3
O2 h
O3
OH HO2
h, H2O
Deposition
NO
H2O2
CO, VOC
NO2
h
STRATOSPHERE
TROPOSPHERE
8-18 km
Chem prod in troposphere,
Tg y-1
4300
1600
Chem loss in troposphere,
Tg y-1
4000
1600Transport from stratosphere,
Tg y-1
400
400
Deposition,
Tg y-1700
400Burden, Tg 360
230
Lifetime, days 28
42
Present-day Preindustrial
CARBON MONOXIDE IN ATMOSPHERECARBON MONOXIDE IN ATMOSPHERE
Source: incomplete combustionSink: oxidation by OH (lifetime of 2 months)
SATELLITE OBSERVATION OF CARBON MONOXIDESATELLITE OBSERVATION OF CARBON MONOXIDE
MOPITT CO columns(Mar-Apr 01)
SATELLITE OBSERVATIONS OF BIOMASS FIRES SATELLITE OBSERVATIONS OF BIOMASS FIRES (1997)(1997)
SHORT QUESTIONSSHORT QUESTIONS
1. How does a thinning of the stratospheric ozone layer affect tropospheric OH concentrations?
2. 2. If the CO source to the atmosphere were to double, would the CO concentration (a) double, (b) less than double, (c) more than double?
3. Methylperoxy radicals produced from methane oxidation can self-react to form methanol: CH3O2 + CH3O2 CH3OH + CH2O + O2
What is the effect of this reaction on OH levels?
METHANE: #2 ANTHROPOGENIC GREENHOUSE GASMETHANE: #2 ANTHROPOGENIC GREENHOUSE GASGreenhouse radiative forcing of climate between 1750 and 2005 [IPCC, 2007]
Referenced to concentration Referenced to emission
GLOBAL METHANE SOURCES, Tg a-1 [IPCC, 2007]
ANIMALS80-90
LANDFILLS40-70
GAS50-70
COAL30-50RICE
30-110
TERMITES20-30
WETLANDS100-230
BIOMASSBURNING10-90
GLOBAL DISTRIBUTION OF METHANEGLOBAL DISTRIBUTION OF METHANENOAA/CMDL surface air measurementsNOAA/CMDL surface air measurements
Sink: oxidation by OH (lifetime of 10 years)
HISTORICAL TRENDS IN METHANEHISTORICAL TRENDS IN METHANE
The last 1000 years
The last 20 years
IPCC [2007]
600
800
700
Scenarios
A1BA1TA1F1A2B1B2IS92a
900
Year
IPCCIPCC [2001] Projections of Future [2001] Projections of Future CHCH44 Emissions (Tg CH Emissions (Tg CH44) to 2050) to 2050
2000 2020 2040
NONOxx EMISSIONS (Tg N a EMISSIONS (Tg N a-1-1) TO TROPOSPHERE) TO TROPOSPHERE
FOSSIL FUEL 23.1
AIRCRAFT 0.5
BIOFUEL 2.2
BIOMASSBURNING 5.2
SOILS 5.1
LIGHTNING 5.8
STRATOSPHERE 0.2
USING SATELLITE OBSERVATIONS OF NOUSING SATELLITE OBSERVATIONS OF NO22 TO MONITOR NO TO MONITOR NOxx EMISSIONS EMISSIONS
SCIAMACHY data. May-Oct 2004
(R.V. Martin, Dalhousie U.)
detectionlimit
NITROGEN DIOXIDE FROM THE OMI SATELLITE (MARCH 2006)NITROGEN DIOXIDE FROM THE OMI SATELLITE (MARCH 2006)
March 2006
LIGHTNING FLASHES SEEN FROM SPACE (2000)LIGHTNING FLASHES SEEN FROM SPACE (2000)
DJF
JJA
PEROXYACETYLNITRATE (PAN) AS RESERVOIR PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NOFOR LONG-RANGE TRANSPORT OF NOxx
NOAA/ITCT-2K2 AIRCRAFT CAMPAIGN IN APRIL-MAY 2002 NOAA/ITCT-2K2 AIRCRAFT CAMPAIGN IN APRIL-MAY 2002 Monterey, CAMonterey, CA
Asian pollution plumes transported to California
CO
O3
PAN
HNO3
May 5 plume at 6 km:High CO and PAN,no O3 enhancement
May 17 subsidingplume at 2.5 km:High CO and O3,PAN NOxHNO3
Hudman et al. [2004]
NOx
NOx
HNO3
PAN
O3
CO
TROPOSPHERIC OZONE COLUMN DATA FROM SPACETROPOSPHERIC OZONE COLUMN DATA FROM SPACE
June-August 2006 observations
TROPOSPHERIC OZONE: TROPOSPHERIC OZONE: #3 ANTHROPOGENIC GREENHOUSE GAS#3 ANTHROPOGENIC GREENHOUSE GAS
Greenhouse radiative forcing of climate between 1750 and 2005 [IPCC, 2007]
Referenced to concentration Referenced to emission
IPCC RADIATIVE FORCING ESTIMATE FOR TROPOSPHERIC IPCC RADIATIVE FORCING ESTIMATE FOR TROPOSPHERIC OZONE (0.35 W mOZONE (0.35 W m-2-2) RELIES ON GLOBAL MODELS) RELIES ON GLOBAL MODELS
Preindustrialozone models
}
Observations at mountain sites in Europe [Marenco et al., 1994]
…but these underestimate the observed rise in ozone over the 20th century
Fitting to observations would imply a radiative forcing of 0.8 W m-2
1996-2005 NO1996-2005 NOxx EMISSION TREND SEEN FROM SPACE EMISSION TREND SEEN FROM SPACE
Van der A et al., 2008
RECENT TRENDS IN TROPOSPHERIC OHRECENT TRENDS IN TROPOSPHERIC OHinferred from methylchloroform observationsinferred from methylchloroform observations