Connecting atmospheric composition with climate variability and change
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Transcript of Connecting atmospheric composition with climate variability and change
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Connecting atmospheric composition with climate variability and change
Seminar in Atmospheric Science, EESC G9910
Diagnosing ENSO from atmospheric composition
(ozone measured from space)Ziemke et al., 2010; Oman et al., 2011
To be discussed Week 4
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Course Information
Two motivating questions:1) How does climate variability (and change) influence
distributions of trace species in the troposphere?2) How do changes in trace species alter climate?
Email me by Monday Sept 10: a) to sign up for presentation:
amfiore @ ldeo.columbia.edub) Credit options:
1 point (discussion only) 2 points (discussion + presentation)
Weekly readings at www.ldeo.columbia.edu/~amfiore/eescG9910.html
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Today’s Outline
1.Overview of composition-climate interactions
2.Intro to key concepts a. Units of atmospheric composition
b. Budgets / Lifetimes c. Radiative Forcing
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Big Issues in Atmospheric Chemistry
LOCAL < 100 km
REGIONAL100-1000 km
GLOBAL > 1000 km
Urban smog
Point source
Disasters Visibility
Regional smog
Acid rain
Ozonelayer
Climate
Biogeochemical cycles
Daniel Jacob
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From Brasseur & Jacob,Ch2, draft chapterJan 2011 version; Text in prep
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Air pollutants affect climate; changes in climate affect global atmospheric chemistry (and regional
air pollution)
NMVOCsCO, CH4
NOx
pollutant sources
+
O3
+OH
H2O
Black carbonSulfate
organic carbon
T T
Aerosols interact with sunlight“direct” + “indirect” effects
Surface of the Earth
Greenhouse gasesabsorb infrared radiation
T
atmospheric cleanser
Smaller droplet sizeclouds last longer increase albedo less precipitation
A.M. Fiore
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Climate (change) affects chemistry (and air quality)
sourcesstrong mixing
(1) Transport / mixing (e.g., distribution of trace species)Exchange with stratosphere
(3) Chemistry responds to changes in temperature, humidityNMVOCsCO, CH4
NOx+ O3+ OHH2O
PAN
(2) Emissions (biogenic, lightning NOx, fires)
VOCs
Planetary boundary layertropopause
A.M. Fiore
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1.1 Mixing ratio or mole fraction CX [mol mol-1]# moles of Xmole of airXC remains constant when air density changes
e robust measure of atmospheric composition
SPECIES MIXING RATIO (dry air)[mol mol-1]
Nitrogen (N2) 0.78
Oxygen (O2) 0.21
Argon (Ar) 0.0093
Carbon dioxide (CO2) 380x10-6
Neon (Ne) 18x10-6
Ozone (O3) (0.01-10)x10-6
Helium (He) 5.2x10-6
Methane (CH4) 1.7x10-6
Krypton (Kr) 1.1x10-6
Tracegases
Air also contains variable H2O vapor (10-6-10-2 mol mol-1) and aerosol particles
Trace gas concentration units: 1 ppmv = 1 µmol mol-1 = 1x10-6 mol mol-1
1 ppbv = 1 nmol mol-1 = 1x10-9 mol mol-1
1 pptv = 1 pmol mol-1 = 1x10-12 mol mol-1Daniel Jacob
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1.2 Number density nX [molecules cm-3]
# molecules of Xunit volume of airXn
Proper measure for• reaction rates• optical properties of atmosphere
0
Column concentration = ( )X Xn z dz
Proper measure for absorption or scattering of radiation by atmosphere
nX and CX are related by the ideal gas law:
vX a X X
A Pn n C CRT
Also define the mass concentration (g cm-3):
mass of Xunit volume of air
X XX
v
M nA
na = air densityAv = Avogadro’s numberP = pressureR = Gas constantT = temperatureMX= molecular mass of X
Daniel Jacob
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ATMOSPHERIC BUDGET TERMS
GLOBAL SOURCE: emissions, in situ production (Tg yr-1) well-known for some (well-documented) synthetic gases
GLOBAL SINK: chemical destruction, photolysis, deposition (Tg yr-1)
ATMOSPHERIC BURDEN: total mass (Tg) integrated over the atmosphere Well known (measurements) for long-lived (well-mixed) gases Poorly constrained for short-lived species
TREND: difference between sources and sinks (Tg yr-1)
More detail: TAR 4.1.3
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Recent trends in well-mixed GHGshttp://www.esrl.noaa.gov/gmd/aggi/
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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] >25% uncertainty in total emissions
ANIMALS90
LANDFILLS +WASTEWATER
50GAS + OIL60
COAL30RICE 40TERMITES
20
WETLANDS180
BIOMASS BURNING + BIOFUEL 30
GLOBAL METHANESOURCES
(Tg CH4 yr-1)
PLANTS?
60-240 Keppler et al., 2006 85 Sanderson et al., 200610-60 Kirschbaum et al., 2006 0-46 Ferretti et al., 2006
Clathrates?Melting permafrost?
A.M. Fiore
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Lifetimes
Atmospheric Lifetime: Amount of time to replace burden (turnover time)
t (yr) = burden (Tg) / mean global sink (Tg yr-1) for a gas in steady-state (unchanging burden; sources = sinks
Convenient scale factor: (1) constant emissions (Tg/yr) steady-state burden (Tg)(2) emission pulse (Tg) time integrated burden of that pulse (Tg/yr)
Perturbation (e-folding) Time – can differ from the atmospheric steady-state lifetime only equal to atmospheric lifetime for gases with constant chemical lifetime
(e.g., Rn, radioactive decay) Chemical feedbacks
(e.g., CH4: more CH4, longer CH4 lifetime; N2O: more N2O, shorter lifetime
Lifetimes can vary spatially and temporally-- species with lifetimes shorter than mixing time scales (< 1 year)
(TAR 4.1.4)
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TIME SCALES FOR HORIZONTAL TRANSPORT(TROPOSPHERE)
2 weeks1-2 months
1-2 months
1 year
c/o Daniel Jacob
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TYPICAL TIME SCALES FOR VERTICAL MIXING
0 km
2 km1 day
planetaryboundary layer
tropopause
5 km
(10 km)
1 week1 month
10 years
c/o Daniel Jacob
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Radiative Forcing (RF): A convenient metric for comparing climate responses
to various forcing agents
RF = Change in net (down-up) irradiance (radiative flux) at the tropopause due to a perturbation to an atmospheric constituent
DTs = l * RF
Climate sensitivityparameter
Global, annual mean change in surface T in responseto RF (equilibrium)
Why is this convenient/useful ? First order estimate, best for LLGHGs Relatively easy to calculate (as opposed to climate response) Related to global mean equilibrium T change at surface:
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uv visnear-ir longwave
Methane
Nitrous oxide
Oxygen; Ozone
Carbon dioxide
Water vapor
Solarblackbody
fn.
Earth’s “effective”
blackbody fn.
CFCs
Clouds,Aerosols
activethroughout
spectra
c/o V. Ramaswamy
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IR Transmission/Absorption in/near atmospheric window
From Jan 2012 version Ch 5 of Brasseur & Jacob textbook in prep
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Radiative Forcing: Analytical expressions for Well-mixed GHGs
From IPCC TAR CH6, Table 6.2http://www.esrl.noaa.gov/gmd/aggi/
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Radiative Forcing (RF): comparison of calculation methodologies
Figure 2.2, WG1 IPCC AR-4 Chapter 2, Section 2.2
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Radiative forcing of climate (1750 to present):Important contributions from non-CO2 species
IPCC, 2007
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Global Warming Potentials
• Radiative forcing does not account for different atmospheric lifetimes of forcing agents
• GWP attempts to account for this by comparing the integrated RF over a specified period (e.g. 100 years) from a unit mass pulse emission, relative to CO2.
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WHAT IS THE ATMOSPHERE?
• Gaesous envelope surrounding the Earth
• Mixture of gases, also contains suspended solid and liquid particles (aerosols)
Aerosol = dispersed condensed phase suspended in a gas
Aerosols are the “visible” components of the atmosphere
The atmosphere seen from space
Pollution off U.S. east coast Dust off West AfricaCalifornia fire plumes
Daniel Jacob
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ATMOSPHERIC GASES ARE “VISIBLE” TOO…IF YOU LOOK IN THE UV OR IR
Nitrogen dioxide (NO2 ) observed by satellite in the UV
Daniel Jacob