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
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
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
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
From Brasseur & Jacob,Ch2, draft chapterJan 2011 version; Text in prep
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
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
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
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
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
Recent trends in well-mixed GHGshttp://www.esrl.noaa.gov/gmd/aggi/
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
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)
TIME SCALES FOR HORIZONTAL TRANSPORT(TROPOSPHERE)
2 weeks1-2 months
1-2 months
1 year
c/o Daniel Jacob
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
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:
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
IR Transmission/Absorption in/near atmospheric window
From Jan 2012 version Ch 5 of Brasseur & Jacob textbook in prep
Radiative Forcing: Analytical expressions for Well-mixed GHGs
From IPCC TAR CH6, Table 6.2http://www.esrl.noaa.gov/gmd/aggi/
Radiative Forcing (RF): comparison of calculation methodologies
Figure 2.2, WG1 IPCC AR-4 Chapter 2, Section 2.2
Radiative forcing of climate (1750 to present):Important contributions from non-CO2 species
IPCC, 2007
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.
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
ATMOSPHERIC GASES ARE “VISIBLE” TOO…IF YOU LOOK IN THE UV OR IR
Nitrogen dioxide (NO2 ) observed by satellite in the UV
Daniel Jacob
