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? me by Monday Sept 10: a) to sign up for presentation: ldeo.columbia.edu b) Credit options: 1 point (discussion only) 2 points (discussion + presentation) Weekly readings at

Today’s Outline 1.Overview of composition-climate interactions 1.Intro to key concepts a. Units of atmospheric composition b. Budgets / Lifetimes c. Radiative Forcing

Big Issues in Atmospheric Chemistry LOCAL < 100 km REGIONAL km GLOBAL > 1000 km Urban smog Point source Disasters Visibility Regional smog Acid rain Ozone layer Climate Biogeochemical cycles Daniel Jacob

From Brasseur & Jacob, Ch2, draft chapter Jan 2011 version; Text in prep

Air pollutants affect climate; changes in climate affect global atmospheric chemistry (and regional air pollution) NMVOCs CO, CH 4 NO x pollutant sources + O3 O3 + OH H2OH2O Black carbon Sulfate organic carbon T T Aerosols interact with sunlight “direct” + “indirect” effects Surface of the Earth Greenhouse gases absorb infrared radiation T atmospheric cleanser Smaller droplet size  clouds last longer  increase albedo  less precipitation A.M. Fiore

Climate (change) affects chemistry (and air quality) sources strong mixing (1) Transport / mixing (e.g., distribution of trace species) Exchange with stratosphere (3) Chemistry responds to changes in temperature, humidity NMVOCs CO, CH 4 NO x + O3 O3 + OH H2OH2O PAN (2) Emissions (biogenic, lightning NO x, fires) VOCs Planetary boundary layer tropopause A.M. Fiore

1.1 Mixing ratio or mole fraction C X [mol mol -1 ] remains constant when air density changes  robust measure of atmospheric composition SPECIESMIXING RATIO (dry air) [mol mol -1 ] Nitrogen (N 2 )0.78 Oxygen (O 2 )0.21 Argon (Ar) Carbon dioxide (CO 2 )380x10 -6 Neon (Ne)18x10 -6 Ozone (O 3 )( )x10 -6 Helium (He)5.2x10 -6 Methane (CH 4 )1.7x10 -6 Krypton (Kr)1.1x10 -6 Trace gases Air also contains variable H 2 O vapor ( 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 = 1x mol mol -1 Daniel Jacob

1.2 Number density n X [molecules cm -3 ] Proper measure for reaction rates optical properties of atmosphere Proper measure for absorption or scattering of radiation by atmosphere n X and C X are related by the ideal gas law: Also define the mass concentration (g cm -3 ): n a = air density A v = Avogadro’s number P = pressure R = Gas constant T = temperature M X = 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 GHGs

More than half of global methane emissions are influenced by human activities ~300 Tg CH 4 yr -1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005] ~200 Tg CH 4 yr -1 Biogenic sources [Wang et al., 2004] >25% uncertainty in total emissions ANIMALS 90 LANDFILLS + WASTEWATER 50 GAS + OIL 60 COAL 30 RICE 40 TERMITES 20 WETLANDS 180 BIOMASS BURNING + BIOFUEL 30 GLOBAL METHANE SOURCES (Tg CH 4 yr -1 ) PLANTS? Keppler et al., Sanderson et al., Kirschbaum et al., Ferretti et al., 2006 Clathrates? Melting permafrost? A.M. Fiore

Lifetimes Atmospheric Lifetime: Amount of time to replace burden (turnover time)  (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 weeks 1-2 months 1 year c/o Daniel Jacob

TYPICAL TIME SCALES FOR VERTICAL MIXING 0 km 2 km 1 day planetary boundary layer tropopause 5 km (10 km) 1 week 1 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  T s =  RF Climate sensitivity parameter Global, annual mean change in surface T in response to 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:

uvvis near-ir longwave Methane Nitrous oxide Oxygen; Ozone Carbon dioxide Water vapor Solar blackbody fn. Earth’s “effective” blackbody fn. CFCs Clouds, Aerosols active throughout 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 6.2

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-CO 2 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 (NO 2 ) observed by satellite in the UV Daniel Jacob