Prof. V. Faye McNeill Department of Chemical Engineering. Columbia University Summer. Teachers August 19, 2009

Transcription

1 Atmospheric Particles, Clouds, and Climate Prof. V. Faye McNeill Department of Chemical Engineering Columbia University Summer Research hprogram for Science Si Teachers August 19, 2009 Image from NASA MODIS sattelite

2 Atmospheric composition: what, and how much? GASES: mostly N 2, O 2 N 2 78% (p N2 = 0.78 atm) O 2 21% (p O2 = 021atm) 0.21 Ar 0.93% (p Ar = atm) Ar interesting gases present at other trace levels p 4 CO2 = 3x10 4 atm N 2 p O3 = 5x10 8 atm many, many more. O 2 N 2 2

3 Atmospheric composition: Condensed phase Clouds/fog Water droplets orsolid (ice) ~5 μm < D p < 50 μm (1 μm = 1 millionth of a meter = 1/100 th the thickness of a human hair!) Particles aerosols 2 nm < D p < 20 μm Highly varied composition Phase: Solid, liquid, or complex ~10 3 particles/cc Lifetime in atmosphere ~ 7 days Leck and Bigg, GRL 2005 Aerosol definition: suspension of condensed phase particles in gas 2

4 Atmospheric particles: Impact Air quality Health effects Visibility Atmospheric chemistry CLIMATE

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6 Atmospheric aerosols: sources Primary Direct emission Examples: dust, sea salt Often larger in size Secondary Formed via chemical or physicalprocesses processes in situ Freshly nucleated new particles: smallest size fraction Leads to mixed inorganicorganic composition Local Regional Long range Man made vs. Natural? 5

7 Air Quality, Air Pollution and Atmospheric Chemistry Goal: improve Air Quality reducenegativehealth effects (e.g. respiratory, toxics exposure) other concerns (visibility, increased UV, global warming) typical metrics: p O3, PM10, PM2.5 What do we have control over? emissions from human activities ( Air Pollution ) provides indirect control of air quality (Example: Secondary Organic Aerosol) Atmospheric chemistry describes the network of chemical processes that links human activities to atmospheric composition and air quality. 6

8 The role of Atmospheric Chemistry Human activities IN Atmospheric Chemistry and Physics OUT Air Quality How healthy is the air we breathe? Climate Important factors for AQ: conc. of small particles (PM2.5) ozone (O3) concentration 8 3

9 from D. Jacob

10 Greenhouse gases 9

11 Millenial NH temperature trend [IPCC, 2001] 10

12 GLOBAL CLIMATE CHANGE SINCE 1850 [IPCC, 2007] c.ch 11

13 Arctic sea ice melt

14 .ch ww.ipcc. ww Aerosols probably have a net cooling effect on climate. Large error bars!

15 Aerosol direct effects Aerosols scatter solar radiation increase the Earth s albedo negative climate forcing (cooling) global dimming e.g. haze particles Some aerosols also absorb radiation Positive climate forcing (warming) e.g. Black carbon (smoke), dust, Absorbance (A AU) Initial glyoxal concentration 2.21 M 175M M 0.70 M 0.22 M 0 M some organic aerosols Wavelength (nm)

16 SCATTERING vs. ABSORBING AEROSOLS S Scattering sulfate and organic aerosol over Massachusetts Partly absorbing dust aerosol downwind d of Sahara Absorbing aerosols (black carbon, dust) warm the climate by absorbing solar radiation 14

17 Aerosols and clouds: the indirect effects 15 Clouds form when water vapor in the air condenses to make small droplets or ice particles. Clouds form more easily when there are particles in the air to act as condensation nuclei

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19 The aerosol indirect effects Aerosol particles act as cloud condensation nuclei. more aerosols more cloud droplets more growing droplets compete for same water vapor smaller cloud droplets brighter clouds suppressed precipitation 16

20 Aerosols and Climate 17 From the IPCC report,

21 EVIDENCE OF INDIRECT EFFECT: SHIP TRACKS N ~ 40 cm -3 N ~ 100 cm -3 W ~ 0.30 g m -3 W ~ 0.75 g m -3 r r e ~ 10.5 µm e ~ 11.2 µm from D. Rosenfeld Particles emitted by ships increase concentration of cloud condensation nuclei (CCN) Increased CCN increase concentration of cloud droplets and reduce their avg. size Increased concentration and smaller particles reduce production of drizzle Liquid water content increases because loss of drizzle particles is suppressed Clouds are optically thicker and brighter along ship track 18

22 SATELLITE IMAGES OF SHIP TRACKS NASA, 2002 NASA Atlantic, France, Spain AVHRR, 27. Sept. 1987, 22:45 GMT US-west coast 19

23 EVIDENCE OF AEROSOL EFFECTS ON CLIMATE: Temperature decrease following large volcanic eruptions erature ge ( o C) Tempe Chang Observations NASA/GISS general circulation model Mt. Pinatubo eruption 20

24 .ch ww.ipcc. ww Aerosols probably have a net cooling effect on climate. Large error bars!

25 Response to climate change: What do we do now? LONG TERM Paradigm shift to drastically reduce CO 2 emissions NEAR TERM Carbon capture and sequestration Emergency measures? Geoengineering: Inject extra aerosols into stratosphere, induce cooling via the aerosol direct effect (but what about aerosols roles in atmospheric chemistry and air quality?) 21

26 Aerosol Characterization: What do we want to know? Total number or mass of particles (loading) Size distribution Smallerparticles pose greater health risk Particle composition Toxicology (e.g. PAHs) Optical properties 22 Num mber of particles per cm Particle diameter, Dp (nm) Measured outside Mudd, June Max PM2.5 this day: 49 μg/m 3 3

27 Measuring particle composition Offline (e.g. filter sampling, denuder, impactor) Relatively easy, cheap, low tech Long sampling times means low time resolution Loss of semivolatile compounds High size cutoff Online (real time data) Aerodyne Mass Spectrometer Single Particle Mass Spectrometers Aerosol CIMS impactor 23 3

28 Chemical Ionization Mass Spectrometry (CIMS) Gas (& particle) )p phase detection 14x10 4 ppt level sensitivity Near real time (0.1 Hz) sampling Versatile but selective Used in a variety of laboratory & field settings Signal (cps) 1.4x Mass (amu)

29 Detection of particle-phase organics using Aerosol CIMS Continuous Heated Flow 3, OH, NO Volatilization Inlet O 3, H 2 O 3 CH 3 I/N 2 Flow Photocell tube Aerosols 210 Po To DMA, CPC I - (H 2 O) + RCOOH I - (RCOOH) + H 2 O Turbo pump 2.0x10 5 ps) Signal (c Turbo pump I amu Chemical Ionization Region To pumps 4000 I - H 2 O 145 amu Sig gnal (cps) I - oleic acid 409 amu 410 Mass (amu) Detection limit ~1 μg m amu Sensitivity ~300 μg 1 m Low fragmentation Mass (amu) 25

30 AC-CIMS: Aerosol Concentrating Mass Spectrometry CIMS sensitivity to aerosol components limited by low total aerosol number, variety of species in ambient air (10 (~10 3 cm 33 ) Solution: Aerosol concentration prior to volatilization (theoretical detection limit: 1.3 ng m 3 ) Method: Aerodynamic & electrostatic focusing, separation 26

31 McNeill Columbia: Techniques for studying Atmospheric Aerosol Chemistry Aerosol Chemistry N 2 O 5 Aerosol Flow Tube Aerosol reactors + Aerosol CIMS ab initio Quantum Mechanics simulations Surface analysis: Ellipsometry, Pendant tdrop tensiometry t VFT SMPS Ozone Scrubber Teflon Prechamber 27

32 McNeill Group Aerosol Chamber Observe gasaerosol interactions Test for changes in aerosol properties Residence time of several hours 30

33 Resources The Earth Institute at Columbia University Lenfest Center for Sustainable Energy NASA GISS gov Lamont Doherty Earth Observatory 33

34 Information about air quality online A B C 34

35 Acknowledgements Daniel Jacob (Harvard) McNeill group (Columbia): Neha, Allie, Min, Julia, Coty, Erica, Erin, Michael, Sophie, Wayne NASA NSF DHS