1. ATMOSPHERIC CHEMISTRY MOPITT and aircraft pictures from http://www.ncar.ucar.edu/ncar/, cloud and surface T figures from http://earthobservatory.nasa.gov/, Hurricaine Alberto (Aug. 2000) and Europe’shttp://www.ncar.ucar.edu/ncar/http://earthobservatory.nasa.gov/ lights from http://eospso.gsfc.nasa.gov/, haze off of Eastern US, TOMS Ozone hole (Oct 2001) courtesy http://visibleearth.nasa.gov/, smokestack from http://www.plantexpansion.orghttp://eospso.gsfc.nasa.gov/http://visibleearth.nasa.gov/http://www.plantexpansion.org

2. ATS 621: ATMOSPHERIC CHEMISTRY Fall 2008 Instructor: Colette L. Heald (heald@atmos.colostate.edu), Rm. 107heald@atmos.colostate.edu TA: Mandy Holden (aholden@atmos.colostate.edu), Rm. 111aholden@atmos.colostate.edu Class Hours: Tues/Thurs 10-10:50am Text: Introduction to Atmospheric Chemistry (D.J. Jacob) Complementary Text: Atmospheric Chemistry and Physics: from Air Pollution to Climate Change (Seinfeld and Pandis) Acknowledgements for class materials: Daniel Jacob and Lyatt Jaegle

3. IMPORTANCE OF ATMOSPHERIC CHEMISTRY Climate Change (…1990s…) Regional Air Pollution (…1950s…) Acid rain (1970s…) Stratospheric Ozone depletion (1985…) Atmospheric CHEMISTRY

4. URBAN/REGIONAL AIR POLLUTION Global air pollution Tropospheric ozone column: Jun-Aug 1948 – noontime (PA) LA

5. ACID RAIN Tropospheric ozone column: Jun-Aug 1989-19911997-1999 Wet sulfate deposition Getting better in the U.S. … but worsening in Asia

6. STRATOSPHERIC OZONE DEPLETION Tropospheric ozone column: Jun-Aug  Downward trends in stratospheric ozone column on a global scale

7. Large increases in greenhouse gases and aerosols since pre-industrial times CLIMATE CHANGE

8. IMPACTS OF ATMOSPHERIC CHEMISTRY GO BACK EVEN FURTHER…. [Zerefos et al., 2007] Paintings by J.M.W. Turner show light scattering from volcanic aerosol Non-volcanic sunset (1828)Volcanic sunset (1833  Babuyan 1831)

9. BUT REMAINS A CONTEMPORARY ISSUE…

10. 1. MEASURES OF ATMOSPHERIC COMPOSITION (CHAPTER 1)

11. 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 We will use “species” as a generic term to describe a constituent of the atmosphere Aerosols are the “visible” components of the atmosphere Pollution haze over East Coast Dust off West Africa

12. BUT ATMOSPHERIC GASES ARE “VISIBLE” TOO… IF YOU LOOK IN THE UV OR IR NO 2 Columns Observed from the SCIAMACHY Satellite Instrument

13. Fundamental quantities of physics MKScgs(  ) Timess1 Lengthmcm100 Masskgg1000 MKS units = "SI" (standard international units) Once we have defined units (standard measures) for these quantities we can derive for all other quantities of physics.

14. Derived quantities: important combinations of fundamental quantities The relationships between fundamental and derived quantities are intimately tied to the laws of physics. For example, Newton's laws relate familiar quantities (force, energy) to the fundamental quantities. vector

15. PREDICTING ATMOSPHERIC CONCENTRATION OF SPECIES X: solve mass balance (or “continuity”) equation for [X](x,t) local change in concentration with time transport (flux divergence; U is wind vector) chemical production and loss (depends on concentrations of other species) [ ] is our general notation for concentration, but “concentration” is an ambiguous word – we will use three different measures: 1. Mixing ratio (or mole fraction) 2. Number density, mass concentration 3. Partial pressure emission deposition

16. 1.1 Mixing ratio or mole fraction C X [mol mol -1 ] remains constant when air density changes  robust measure of atmospheric composition GASMIXING RATIO (dry air) [mol mol -1 ] Nitrogen (N 2 )0.78 Oxygen (O 2 )0.21 Argon (Ar)0.0093 Carbon dioxide (CO 2 )365x10 -6 Neon (Ne)18x10 -6 Ozone (O 3 )(0.01-10)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 (10 -6 -10 -2 mol mol -1 ) and aerosol particles Trace gas concentration units: 1 ppmv = 1x10 -6 mol mol -1 1 ppbv = 1x10 -9 mol mol -1 1 pptv = 1x10 -12 mol mol -1

17. ATMOSPHERIC CO 2 INCREASE OVER PAST 1000 YEARS Intergovernmental Panel on Climate Change (IPCC) document, 2005 Concentration units: parts per million (ppm) number of CO 2 molecules per 10 6 molecules of air CO 2 CONCENTRATION IS MEASURED AS MIXING RATIO

18. ATMOSPHERIC CO 2 TREND OVER PAST 25 YEARS IPCC [2005]  mol mol -1 is the proper SI unit; ppm, ppmv are customary units

19. EPA SURFACE OZONE AIR QUALITY STANDARD “ 8-hour average of 0.08 ppmv not to be exceeded more than 3x/year”

20. "Perfect Gas" Law PV = N' kT or PV = N RT N' = number of molecules in the air parcel N = number of moles; N' = N x A v k = Boltzmann constant R = Universal Gas Constant; R = k x A v ================================= (In meteorology texts: P =  RT - different "R“ = 287 J/kg/K) k = 1.3806503 × 10 -23 m 2 kg s -2 K -1 R = 8.31 J mole -1 K -1

21. 1.2 Number density n X [molecules cm -3 ] Proper measure for reaction rates optical properties of atmosphere Proper measure for absorption 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 [Pa] R = Universal gas constant = A v k k=Boltzmann cnst T = temperature [K] M X = molecular weight of X [g/mol]

22. LAST WEEK’S STRATOSPHERIC OZONE LAYER Method: UV solar backscatter Scattering by Earth surface and atmosphere   Ozone layer Ozone absorption spectrum   http://jwocky.gsfc.nasa.gov/ 1 “Dobson Unit (DU)” = 0.01 mm ozone at STP = 2.69x10 16 molecules cm -2 THICKNESS OF OZONE LAYER IS MEASURED AS A COLUMN CONCENTRATION

23. ANNUAL MEAN PARTICULATE MATTER (PM) CONCENTRATIONS AT U.S. SITES, 1995-2000 EPA particulate matter assessment document (NARSTO), 2003 PM2.5 (aerosol particles < 2.5  m diameter) U.S. air quality standard: PM2.5 = 15  g m -3 (annual mean) Red circles indicate sites in violation of the standard STANDARD IS EXPRESSED AS A MASS CONCENTRATION PER UNIT VOLUME

24. SPECIFIC ISSUES FOR AEROSOL CONCENTRATIONS A given aerosol particle is characterized by its size, shape, phase, and chemical composition – large number of variables! Measures of aerosol concentrations must be given in some integral form, by summing over all particles present in a given air volume that have a certain property The aerosol size distribution must be treated as a continuous function Typical U.S. aerosol size distributions by volume URBAN RURAL

25. 1.3 Partial pressure P x [Pa] Dalton’s law:Proper measure for phase change (such as condensation of water vapour) Evaporation of liquid water from a pan: Add a lid: escaping water molecules collide on lid and return to surface; collision rate measures P H2O eventually, flux escaping = flux returning : saturation (P H2O,SAT ) cloud formation in atmosphere requires P H2O > P H2O,SAT T  P H2O,SAT No lid: water molecules escape from pan to atmosphere (evaporation)

26. Evaporation and condensation are dynamic processes always taking place at the liquid-air interface. When the rate of evaporation equals the rate of condensation, the air and water are in equilibrium, and the air is said to be saturated with water vapour. The relationship between water vapour pressure and temperature is the Clausius-Clapeyron equation. Δ H vap = molar enthalpy of vaporization Vapour Pressure of Water: The pressure of H 2 O vapour in equilibrium with liquid water. Clausius-Clapeyron relation:  Vapour pressure increases sharply with temperature, due to the large latent heat. A=6.11 mbar (= P vap at 0C) B=5308 K

27. PHASE DIAGRAM FOR WATER Dew point: Temperature T d such that P H2O = P H2O,SAT (T d ) gas-liquid metastable equilibrium Latest Observation for Fort Collins, CO (80523) Site: on CSU campus Time: 9 AM MST 25 AUG 08 Temp: 72.6 F (22.5 C) Dewpt: 54.4 F (12.4 C) Rel Hum: 53% Winds: 1 m/s (from W) Pressure: 849.4 mb triple point of water (n=0)

28. RUNAWAY GREENHOUSE EFFECT ON VENUS EARTHVENUS due to accumulation of water vapor from volcanic outgassing early in its history …did not happen on Earth because farther from Sun; as water accumulated it reached saturation and precipitated, forming the oceans

29. WHY CAN YOU SEE YOUR BREATH ON COLD MORNINGS? Draw mixing lines (dashed) to describe dilution of your breath plume w/outside air Your breath 37 o C, ≈ 100%RH warm outside air cold outside air P H2O is plotted on linear scale (vs. log on previous plots) to draw the mixing lines ICE LIQ GAS

30. CONVERTING BETWEEN DIFFERENT MEASURES OF CONCENTRATION CxCx PxPx nxnx

31. RAOULT’S LAW water saturation vapor pressure over pure liquid water surface water saturation vapor pressure over aqueous solution of water mixing ratio x H2O An atmosphere of relative humidity RH can contain at equilibrium aqueous solution particles of water mixing ratio solute molecules in green

32. AIR POLLUTION HAZE “clean” day “moderately polluted” day http://www.hazecam.net/ Views of Acadia National Park Visibility is limited by high concentrations of aerosol particles that have swollen to large sizes due to high relative humidity

33. water droplet, p water = p 0 water lower humidity evaporates water+salt droplet, p water < p 0 water lower humidity gets smaller higher concentration of salt, lower concentration of water The water+salt droplet will shrink when RH declines, but there is a limit…

34. HOWEVER, AEROSOL PARTICLES MUST ALSO SATISFY SOLUBILITY EQUILIBRIA Consider an aqueous sea salt (NaCl) particle: it must satisfy This requires: At lower RH, the particle is dry.

35. UPTAKE OF WATER BY AEROSOLS: HAZE Deliquescence RH; depends on particle composition