Presentation on theme: "Presentation Slides for Air Pollution and Global Warming: History, Science, and Solutions Chapter 5: Aerosol Particles in the Polluted and Global Environment."— Presentation transcript:
1 Presentation Slides for Air Pollution and Global Warming: History, Science, and Solutions Chapter 5: Aerosol Particles in the Polluted and Global Environment By Mark Z. Jacobson Cambridge University Press (2012) Last update: February 1, The photographs shown here either appear in the textbook or were obtained from the internet and are provided to facilitate their display during course instruction. Permissions for publication of photographs must be requested from individual copyright holders. The source of each photograph is given below the figure and/or in the back of the textbook.
2 Salt Lake CityRush Spedden; rmcleanair.blogspot.com/2007/01/utah-choking-on-pollution.html
8 Particle Mixing State External mixture Particle composition is the same as that when the particle was emitted.Internal mixtureParticle composition differs from that when it was emitted due to condensation, dissolution, coagulation, and other physical processes affecting composition.
9 Internally- and Externally-Mixed Soot Particles Soot inclusionPósfai et al. (1999)Strawa et al. (1999)
12 Particle Size Distribution Variation of particle concentration (i.e., number, surface area, volume, or mass of particles per unit volume of air) with size.Size distribution usually divided into modesMode Diameter Range (nm)Nucleation < 100Submode 1 <10SubmodeAccumulation 100 – 2500Submode 1 ~ 200Submode 2 ~Coarse > 2500
13 Lognormal Distribution Describes an individual mode of a size distribution
14 Ambient Size Distribution Mode Diameter Range (nm)Nucleation < 100AccumulationSubmode 1 ~ 200Submode 2 ~Coarse > 2500Claremont, California,Aug., 1987Figure 5.2
15 Major Particle Emission Sources Sea spraySoil dustVolcanosBiomass burningFossil-fuel combustionIndustrialMiscellaneous
16 Sea Spray EmissionForm when winds and waves force air bubbles to burst at sea surfaceContain composition of sea waterSpume dropsDrops larger than sea spray form when winds tear off wave crests.Sea-spray acidificationReduction in chloride in sea spray drops as sulfuric acid or nitric acid enter the drops.DehydrationWater loss when drop evaporates in low relative-humidity air
17 Constituents of Sea Water Constituent Mass percentWaterSodium 1.05Chlorine 1.88MagnesiumSulfurCalciumPotassiumCarbonTable 5.3
18 Dust Storm From Africa (Feb. 28, 2000) NASA/Goddard Space Flight Center and ORBIMAGE
19 Soil Dust Emission Soil Natural, unconsolidated mineral and organic matter lying above bedrock on the surface of the Earth. Originates from the breakdown of rocks and decay of dead plants and animals.RocksSedimentary: Cover 75 percent of Earth’s surface and form by deposition and cementation of carbonates, sulfates, chlorides, shell fragments. Example: chalk.Igneous: Form by cooling of magma. Example: Granite.Metamorphic: Form by structure transformation of existing rocks due to high temperatures and pressures. Example: marble.
20 Breakdown of Rocks to Soil Physical weatheringDisintegration of rocks and minerals by processes not involving chemical reactions. Examples: when stress applied to a rock. Stresses arise due to high pressure under soil or when rocks freeze/thaw or when saline solutions enter cracks and cause disintegration/fracture.Chemical weatheringDisintegration of rocks and minerals by chemical reaction. Example: Dissolution of gypsum in water:(5.1)
21 Types of Minerals in Soil Dust Quartz - SiO2(s) - clear, colorless, resistant to chemical weatheringFeldspars - 50 percent of rocks on Earth’s surfacePotassium feldspar - KAlSi3O3(s)Plagioclase feldspar - NaAlSi3O3-CaAl2Si2O8(s)Hematite - Fe2O3(s) - reddish brownCalcite - CaCO3(s) - found in limestoneDolomite - CaMg(CO3)2(s)Gypsum - CaSO4-2H2O(s)- colorless to whiteClays - soft, compact, odorous minerals resulting from weatheringKaolinite - Al4Si4O10(OH)8(s)IlliteSmectiteVermiculiteChloriteOrganic matter - plant litter or animal tissue broken by bacteria
22 Time For Particles to Fall 1 km Diam. (mm) Time to Fall 1 kmyyddhmmOnly particles smaller than 10 mm reach the global atmosphereTable 5.4
23 Sarychev, Kuril Islands (June, 2009) NASA Johnson Space Center
24 Volcanic Emission Over 500 volcanos currently active Magma contains 1-4 percent gas by mass.Water vapor makes up percent of gas massSome other constituents:CO2(g) SO2(g)OCS(g) N2(g)CO(g) H2(g)S2(g) HCl(g)Cl2(g) F2(g)ParticlesMost abundant are silicate minerals.Range in size from <0.1 to 100 mm
25 Savannah Fire, Masai Mara, Kenya EricIsselee/Dreamstime.com.
27 Biomass-Burning Emission Burning of evergreen forests, deciduous forests, woodlands, grasslands, agricultural land either to clear land, stimulate grass growth, manage forest growth, or satisfy a ritual.Gas constituentsCO(g) CO2(g)CH4(g) NOx(g)ROG SO2(g)Particle constituentsAsh, plant fibers, soil dust, organic matter, soot (black carbon plus organic matter)Composition of sootHigh temperatures --> high ratio of BC:OM in soot
28 Fossil FuelsCoalCombustible brown-to-black carbonaceous sedimentary rock formed by compaction of partially decomposed plant material.Stages of coal metamorphosisPeat (unconsolidated, brown-black)Peat coal (consolidated, brown-black)Lignite coal (brown-black)Bituminous (soft) coal (dark brown to black)Anthracite (hard) coal (black)Oil (petroleum)Natural greasy, viscous, combustible hydrocarbon liquid that forms from geological-scale decomposition of plants and animals.
29 Fossil-Fuel Combustion Emission GasesNOx(g), ROG(g), CO(g), CO2(g), CH4(g), SO2(g)ParticlesSoot (BC+OM), OM alone, SO42-, metals, fly ashFly ashContains O, Si, Al, Fe, Ca, Mg.
35 CoagulationOccurs when two particles collide and stick together (coalesce).Reduces number concentration but conserves volume concentrationClassic coagulation mechanismsBrownian motionConvective Brownian diffusion enhancementGravitational collectionTurbulent inertial motionTurbulent shearAdditional mechanismsDiffusiophoresisThermophoresisElectric chargevan der Waals forcesFractal geometry effects
38 Condensing GasesCondensation occurs primarily on accumulation mode since it contains the largest surface area concentration of all modes.Water vaporCondenses on accumulation and coarse-mode particles to form cloud dropsSulfuric acidCondensation onto accumulation mode affects visibilityHigh-molecular weight organic gasesProducts of toluene, xylene, alkylbenzene, alkane, alkene, biogenic hydrocarbon oxidation condense onto accumulation mode primarily.
40 Saturation Vapor Pressure of Water Over Liquid Water/Ice Surfaces Figure 5.12
41 Dissolution Dissolution Process by which a gas diffuses to and dissolves in a liquid on a particle surface.SolventA liquid in which a gas dissolvesSoluteGas, liquid, or solid that dissolves in a solventSolutionOne or more solutes plus the solvent.Common dissolving gasesHCl(g), HNO3(g), NH3 (g), SO2(g)
42 Dissociation Dissociation Breakdown of dissolved molecules into ions. CationsPositively-charged ions (e.g., H+, Na+, K+, Ca2+)AnionsNegatively-charged ions (e.g., OH-, Cl-, NO3-, HSO4-, SO42-)ElectrolyteSubstance that undergoes partial or complete dissociation(e.g., NH4NO3, Na2SO4, HCl)
43 Dissolution/Dissociation Addition of acid to solution increases [H+], decreasing pHHydrochloric acidNitric acid(5.6) - (5.8)
44 AcidityMeasure of the concentration of hydrogen ions (H+) in solutionpH = -log10[H+](5.4)[H+] = molarity (M, moles of H+ per liter of solution)Higher [H+] --> lower pH --> more acidic solution
45 Acidity In dilute water, the only source of H+ is (5.5) [H+][OH-] = M2 --> [H+]=[OH-]=10-7 M--> pH = -log10[10-7M] = 7
46 Acid/BaseAcidSubstance that, when added to a solution, dissociates, increasing [H+], decreasing pHStrong acid: Substance that dissociate readily(e.g., H2SO4, HCl, HNO3)Weak acid: Substance that dissociate less readily(e.g., H2CO3)Base (alkali)Substances that, when added to a solution, reduce [H+], increasing pH. (e.g., NH3, Ca(OH)2)
49 Soil-Particle Acidification Addition of acid to calcite-containing soil dust removes carbonate ion(5.9)
50 HydrationBonding of liquid water to solute (anions, cations, or undissociated molecules).The higher the relative humidity and greater the quantity of solute, the greater the liquid water uptake due to hydration.Hydration responsible for swelling of particles sufficiently to cause a haze when the relative humidity is below 100 percent.
51 Sulfuric Acid Condensation/Dissociation Condensation occurs primarily on accumulation mode(5.10)
53 Solid PrecipitationWhen the relative humidity decreases, ions in solutions may combine (crystallize) to form solids (solid precipitation). Solids may also form by chemical reaction on the surface of particles.Common solid formation reactionsNH4+ + NO3- <=> NH4NO3(s) ammonium nitrate2NH4+ + SO42- <=> (NH4)2SO4(s) ammonium sulfateCa2+ + SO H2O(aq) <=> CaSO4-2H2O(s) gypsum
54 Particle Health Effects Hazardous compounds in particlesBenzene, PAHs, metals, sulfur compoundsMetalsLung injury, bronchioconstriction, increased infectionPM10Asthma, chronic obstructive pulmonary disease, increased mortality, higher hospitalization and health-care visits for respiratory and cardiovascular disease. May be no low threshold for health-related problems due to PM10.PM2.5More respiratory illness and premature death than larger particles. Long-term city exposure may reduce life by two years.Total air pollution mortality (due mostly due to particles)2.5-3 million deaths/yr worldwide from air pollution; 1.6 million in due to indoor burning of biomass, coal.
55 Aerosol Particle Composition vs. Size Figure 5.15
56 Lungs of Teenage non-smoking Teenager in Los Angeles, 1970s SCAQMDFigure 5.18