Download
slide1 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Fine Atmospheric Particles: Do we need to worry about them?? PowerPoint Presentation
Download Presentation
Fine Atmospheric Particles: Do we need to worry about them??

Fine Atmospheric Particles: Do we need to worry about them??

135 Vues Download Presentation
Télécharger la présentation

Fine Atmospheric Particles: Do we need to worry about them??

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Fine Atmospheric Particles:Do we need to worry about them??

  2. Almost all combustion leads to the formation of fine particles

  3. Mastery of Fire 400,000 years ago in Europe 100,000 years ago in Africa M. N. Cohne, 1977

  4. Ultimately we learned how to use fire to clear land for crops

  5. In China 2000 years ago the Loess Plateau was the cradle of ancient Chinese civilization. Deforestation due to: Firewood collection Charcoal making Creation of farm land Brick making resulted in a much drier and less productive climate

  6. North American Indians used to burn forested areas to promote the growth of food ”sprouts” • In Mexico deforestation often lead to soil erosion and drier climates (800-1400 before present-BP)

  7. When fire was brought inside the home very large smoke exposures resulted: • These exposures are often much higher in the developing world than in the industrialized world • Women tend to spend more time around unvented fires than men

  8. In Nepal females and their very young children receive much higher exposures to indoor fires than males (Kirk Smith, 1983) • Average cooking time is 2.8 hours • Prevalence of chronic bronchitis is related to hours spent near the stove

  9. Exposures are indoors as well as outdoors Picture by Kirk Smith, India, early 1980s

  10. After a few hours

  11. Acute Respiratory Infections/6 month in Rural Nepal Infants vs. time Near Stove (M. R. Panday, 1984)

  12. Acute Respiratory Infections in Rural Nepal Infants vs. time Near Stove (M. R. Panday, 1984)

  13. Acute Respiratory Infections in Rural Nepal Infants vs. time Near Stove (M. R. Panday, 1984)

  14. Comparative ParticulateConcentrations in mg/m3 • U.S. Standard (PM2.5) 65 • Sydney (1996) ~25 • Traffic- Denmark 60 • London Smog (1952) 4,500 • Muese, Belgium 12,500 • Indian village 1,000(Indoors ) 56,000 • Malaysia (1997, PM2.5) 800 • Thailand (1998, PM2.5) 300

  15. Combustion forms a host of toxics that are associated with soot particles • Polynuclear aromatic hydrocarbons (PAH) • Chlorinated dioxins and furans • Aldehydes and carbonyl compounds

  16. Polynuclear Aromatic Hydrocarbons (PAH) as a class of compounds are considered potential carcinogens

  17. Combustion Formation of PAH Badger and Spotswood 1960

  18. Combustion Formation of Dioxins from Polychlorinated phenol O H C l x . OH Flame C l x . O O H + Polychlorinated Phenol C l y O + OH O C l y O C l x O H C l x C l y Chlorinated dibenzo dioxin Shaub & Tsang, ES&T 1983.

  19. Fresh wood soot in outdoor chambers (0.5 mm scale

  20. Many of these compounds exist as a free gas and on particles. This influences: • how they will be deposited on the earth's surface • the types of chemical reactions they can undergo • the route by which they enter the food chain and are sorbed or deposited in the lungs

  21. Gas Particle Partitioning toxic gas particle

  22. Langmuirian Adsorption (1918) gas surface •  = fraction of total sites occupied • Rateon= kon (Pg) (1- ); • Rateoff= koff; • kon/koff= Keq

  23. Langmuirian Isotherm • if Keq Cgas<< 1; = Keq Cgas

  24. Junge (1977) •  = jcj /(Po + jcj) • = fraction in aerosol phase • Po= sat. vapor pressure of the pure compound • j = conc. of aerosol surface (cm2/cm3) • cj =const, bBET, moles of sites/cm2,temp • cj=RTNse(Qi-Ql)/RT

  25. anthracene A vapor pressure calculation for the liquid vapor for anthracene Tb= 198 + S DTb ; C14H18 anthracene has10, =CH- , carbons and each carbon = 26.73oK/carbon It also has 4, =C< at 31.01OK/carbon Tb = 198 + 267.3 + 124.04 = 589; Published boiling point is = 613K At 298K, lnPoL = -12.76; p = 2.87 x10-6atm = 0.0022 torr

  26. Percent in the Aerosol Phase at Different Aerosol Concentrations (25oC) Phen Pyrene BaP 8x10-4 6x10-5 2x10-7 10g/m3 0.2 2 91 100g/m3 3.1 23 99 500g/m3 18 68 100 rural= 0.5m, high urban 0.35m, Bangkok =0.25m

  27. Yamasaki et al.(1982) • Langmuirian adsorption • Assumes total # sites  TSP (particle conc) • log Ky = -a(1/T)+ b

  28. filter BaA log Ky PUF 1/Tx1000 Yamasaki (1982) • Collects Hi-vol filters+PUF • Analyzes for PAHs

  29. Yamasaki’s relationship • This gives a log Ky = -a(1/T)+ bwhich is compound specific • Ideally from the regression values of a and b, one can estimate the partitioning of a given compound in any atmosphere at a given temp. and TSP

  30. Comparison of Yamasaki predicted vs measured

  31. Application of this theory

  32. A number of years ago we conducted two wood smoke experiments in our Teflon film chambers to evaluate the stability of 9,10 anthraquinone. The average chamber temperature for one experiment was 20oC and the other was 38oC. A third experiment was conducted at 30oC, but only filters were analyzed. Data from these experiments are given below.

  33. UNC 25m3Teflon Film Chambers

  34. Three years later it became very important to know the PUF (gas phase) and particle phase distribution of anthraquinone at the 30oC experiment. It costs, however, 10,000 USD to re-run experiments.

  35. 9,10-anthraquinone data in the gas (PUF) and particle (filter) phases Temp gas (PUF) particle (filter) TSP ng/m3 ng/m3 mg/m3 38oC 228 105 0.512 20oC 38 381 0.366 30oC ? 440 0.832 So what do we do?? lnKy = -a(1/T)+ bTemp is in Kelven

  36. PAHGas PAHpart lnKy = -a(1/T)+ b

  37. log Kp = -log Po(L) + const. Kp= part/(gasxTSP) slope = -1 log Kp • Ambient data of Pankow and Bidleman • PAHs, alkanes • chlorinated organics log Po(L)

  38. For liquid like particles partitioning coefficient, Kp, is: • Kip = 760 RT fomx10-6/{iPLtorrig MWavg} log Kip= - log iPo(L) +C -log ig • C= log [fom (7.501 RT)/ (106Mwom)] • fom = fraction of particle organic mass • Mwom = avg. Mw of om in the particle

  39. Calculating Activity Coefs, ig • RT lnigom= iV[(omdd - idd)2 +ib(omdp - idp)2+ ib(omdh - idh)2] + RT [ln(iV/Vom) +1- iV/Vom] • Vom is the molar volume of the mix • ds are solubility parameters • dd = S Fd,j / iV

  40. Partitioning & uptake by the lungs • Nicotine (Pankow’s group)

  41. Uptake by the lungs (Nicotine) • Under normal circumstances Nicotine can exist as a neutral “free base” or as a protonated mono or di-acid and will appear predominately in the particle phase. • Typically cigarette smoke has pH values ³3 and much of the nicotine exists in the acidified form on particles.

  42. Nicotine • The acidified form can not partition between the gas and particle phase. • If ammonia is added to the tobacco smoke, “as a flavor enhancement”, the pH increases moving the equilibrium on the particles from the mono-acid to the neutral form.

  43. Impact and “advantages” of ammonia “flavor enhancement” on partitioning • In the neutral form nicotine can partition to the gas phase. • neutral nicotine can then be readily absorbed by the wet surface of the inner lung (Pankow’s group) • loss of nicotine to the lungs “pulls” more nicotine off the particles

  44. What are aerosols? • Aerosols are simply airborne particles • They can be solids or liquids or both • They can be generated from some of the following sources:

  45. What are aerosols? • Aerosols are simply airborne particles • They can be solids or liquids or both • They can be generated from some of the following sources: 1. combustion emissions 2. atmospheric reactions 3. re-entrainment

  46. What are some of the terms used to describe aerosols?

  47. What are some of the terms used to describe aerosols? • Diameters are usually used to describe aerosol sizes, but aerosols have different shapes.

  48. Often particles are sized by their aerodynamic diameter • The aerodynamic diameter of a particle is defined as the diameter of an equivalent spherical particle (of unit density) which has the same settling velocity. • It is possible to calculate the settling velocity of a spherical particle with a density =1

  49. Density = mass/volume DensityH20 = 1gram/cm3= 1 • Terminal Settling velocity (Vs ) is the rate that a particle falls due to gravity