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AEROSOLPROZESSE 1. Sichtbare Bedeutung von Aerosolkonzentrationen 2 PM2.5 levels of 5 μg/m3 (left) and 35 μg/m3 (right)"The average annual PM2.5 density.

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Presentation on theme: "AEROSOLPROZESSE 1. Sichtbare Bedeutung von Aerosolkonzentrationen 2 PM2.5 levels of 5 μg/m3 (left) and 35 μg/m3 (right)"The average annual PM2.5 density."— Presentation transcript:

1 AEROSOLPROZESSE 1

2 Sichtbare Bedeutung von Aerosolkonzentrationen 2 PM2.5 levels of 5 μg/m3 (left) and 35 μg/m3 (right)"The average annual PM2.5 density in Beijing has reduced from micrograms per cubic meter of air in the year of 2000 to micrograms per cubic meter in 2010, said Yu Jianhua, an official with Beijing's Municipal Environmental Protection Bureau." EU Direktive zur Luftreinhaltung: Maximalwert 20µg m -3 EU Direktive zur Luftreinhaltung: Maximalwert 20µg m -3

3 Definitions Aerosol: suspension of fine solid or liquid particles in a gas primary aerosol: emitted directly as particles secondary aerosol: formed in the atmosphere by gas-to-particle conversion fine aerosol: particles < 2.5 µm coarse aerosol: particles > 2.5 µm

4 More Definitions dust: solid particles produced by mechanical disintegration of material (D > 1 µm) smoke: small gas-borne particles from incomplete combustion (D > 0.01 µm) fume: solid particles generated from vapour state (usually after volatilization from melted substances) (D < 1 µm) haze: water droplets, pollutants, and dust (D < 1 µm)

5 Chemical composition Tropospheric aerosol contains: sulfate ammonium nitrate sodium chloride trace metals carbonaceous material crustal elements water after Seinfeld&Pandis, 1998

6 Chemical composition (2) 6 Schiffbasierte Messungen von Aerosolen in verschiedenen Weltregionen

7 Chemical composition (3) 7 Mayol-Bocero, 2000 Filterproben aus Messflügen über dem Indischen Ozean

8 Aerosoltypen und Größenverteilung 8 Heintzenberg et al., in Atmospheric Chemistry in a Changing World, Springer, 2003

9 Aerosol size distribution Consider only spherical shape... number density distribution surface distribution volume distribution

10

11 Bedeutung von Aerosolen: Wolken Without particles, no clouds would form! Cloud Condensation Nuclei (CCN): particles that become activated and grow to droplets in the presence of supersaturated water vapour for marine stratiform clouds, the supersaturation is %; minimum particle diameter is nm CCN number concentrations: cm -3 in polluted areas

12 Cloud condensation Liquid Water Content (LWC): L = g H2O /m 3 Droplet size: r = 1 µm - 50 µm

13 Bedeutung von Aerosolen: Strahlung 13 Direkter Effekt Indirekte Effekte

14 14

15 Processes simulated in an atmospheric chemistry transport model 15 Gas photochemistry Gas-to-particle conversion Gas photochemistry Gas-to-particle conversion Gas processes Optical depth of gases/ aerosols/cloud drops Solar radiative transfer Infrared radiative transfer (Visibility) Optical depth of gases/ aerosols/cloud drops Solar radiative transfer Infrared radiative transfer (Visibility) Radiative processes Nucleation Coagulation Condensation/evaporation Dissolution/evaporation Deposition/sublimation Freezing/melting Reversible chemistry Irreversible chemistry Heterogeneous chemistry Nucleation Coagulation Condensation/evaporation Dissolution/evaporation Deposition/sublimation Freezing/melting Reversible chemistry Irreversible chemistry Heterogeneous chemistry Aerosol/cloud processes Wind speed & direction Air pressure Air density Air temperature Soil temperature & humidity Turbulence … Wind speed & direction Air pressure Air density Air temperature Soil temperature & humidity Turbulence … Dynamical/thermodynamical processes Emissions Transport of gases/aerosols/ cloud drops/energy Dry deposition of gases/ aerosols/cloud drops Sedimentation of aerosols/ cloud drops/rain drops Emissions Transport of gases/aerosols/ cloud drops/energy Dry deposition of gases/ aerosols/cloud drops Sedimentation of aerosols/ cloud drops/rain drops Transport processes nach Jacobson, 1999

16 Sources of aerosol (emissions) windborne dust sea spray volcanoes fossil fuel combustion road transport pollen and plant fragments

17 Nucelation – Coagulation - Condensation 17

18 Nucleation 18 J. Pierce, Nature Geoscience 4, 665–666 (2011) Cluster Particles

19 19 P. McMurry (U. Minnesota), Nucleation and Cloud Condensation Nuclei Experiment 2009

20 Absorption equilibrium A(g) A(aq) for dilute solutions: [A(aq)] = H A · p A aqueous-phase concentration (mol L -1 ) Henry coefficient (mol L -1 atm -1 ) partial pressure of A in gas-phase (atm) Gas/Aqueous phase partitioning soluble

21 Gas/Aqueous-phase partitioning very soluble gases: H 2 O 2, HNO 3, NO 3

22 Coagulation 22 Beobachtung des Zusammenwachsens von Wolkentropfen mit gepulster Laserspektroskopie

23 Aerosol processes in clouds 23 C. Hoose et al., 2008

24 Condensation / Evaporation 24 Modelliertes Wolkentröpfchen mit Sulfatmolekülen als Kondensationskeimen

25 Deliquescence and (re)cristallisation The thermodynamic phase of an aerosol particle depends on the humidity. Dry particles will remain solid until the relative humidity reaches a threshold. The, the particle spontaneously absorbs water and grows (deliquescence). Subsequent drying leads to recristallisation, but at much lower relative humidities (Hysteresis effect). Ammonium/Nitrate/Sulfate 30% SO 4, T=298 K

26 Modellierung von Aerosolen 26 Bulk-Schema Bin-Schema Modales Schema Interne Mischung Externe Mischung

27 1.Discretize aerosol distribution in bins and calculate their temporal development: 2. Prescribe aerosol distribution function and calculate the temporal development of its moments: Aerosol Modelling - Methods P. Stier, U. Oxford

28 Comparison bin and modal scheme 28 K. Carslaw and D. Spracklen, U. Leeds

29 Concept of M7 (modal aerosol model) 29 E. Zubler, ETH-Zürich

30 Mixing State of the compounds: Sulfate Black Carbon Organic Carbon Sea Salt Dust Resolve aerosol distribution by 7 log-normal modes Each mode is described by three moments: Number, Median Radius Mass, Standard Deviation (fixed) Reduction of the number of transported tracers to 28 AITKEN (0.005 µm < r < 0.05 µm) ACCUMULATION (0.05 µm < r < 0.5 µm) SOLUBLE / MIXED COARSE (0.5 µm < r ) INSOLUBLE 1 N 1, M SO 4 5 N 5, M BC, M OC 6 N 6, M DU 7 N 7, M DU 2 N 2, M SO 4, M BC, M OC 3 N 3, M SO 4, M BC, M OC, M SS, M DU 4 N 4, M SO 4, M BC, M OC, M SS, M DU NUCLEATION (r < µm) MODES IN M7 Aerosol Representation in ECHAM-HAMMOZ

31 Aerosol Mixing State P. Stier, U. Oxford

32 Evaluation of ECHAM6-HAMMOZ 32 Jan Jul 550 nm

33 Pacific measurement composite (From Clarke and Kapustin; JAS; 2002) 70 S – 20 S Total aerosol number annual mean Pacific profile; Averaged over 70S - 20S and 130 E - 90 W Evaluation of number concentrations P. Stier, U. Oxford

34 Global SO2/SO4 annual budget echam6-hammoz units: Tg (S) SO4 gas SO2SO4 aero DMS-OH DMS-NO3 SO2-OH wetdep drydep emi wetdep drydep wetdep drydep sedi emi condensation nucleation wet chemistry G. Frontoso, ETH-Zürich

35 Multi-Modell Vergleich (AEROCOM) 35

36 Ruß (Black carbon) 36 Ruß entsteht bei der unvollständigen Verbrennung von fossilen Brennstoffen, Holz oder Kohle

37 EXTRA MATERIAL 37

38 Wegener-Bergeron-Findeisen Process 38 Jacobson, p.35

39 pH Upon dissolution in water, several species will form ions, e.g. H 2 O, and CO 2. Water: H 2 O H + + OH - ; equilibrium constant K = [H + ][OH - ] (at 298K, only 2 µmol/L ions versus 55.5 mol/L H 2 O) pH = -log 10 [H + ]

40 Dissolution Generally: K = [X + ][Y - ] / [XY] TABLE6.4

41 CO 2 uptake by the oceans CO 2 (g) CO 2H 2 O CO 2 (aq) = H + + HCO 3 - K c1 H + + CO 3 2- K c2 carbonate bicarbonate K hc total dissolved carbon: effective Henry coefficient

42 CO 2 uptake by the oceans (2)

43 SO 2 uptake by droplets

44 Acidity of (clean) rainwater This can be rearranged to: The atmospheric CO 2 concentration has an influence on the acidity of rain water: Electro neutrality demands that With given temperature and p CO2, [H+] can be computed, from which all other ion concentrations can be deduced. For T=298K and p CO2 = 350 ppm, pH = 5.6 Other species of interest: SO 2 HSO 3 - SO 3 2-, NH 3 NH 4 +, HNO 3 NO 3 -

45 S(IV) S(VI) oxidation The conversion of dissolved SO 2 to sulfate is the most important chemical transformation in cloud water. If one S(IV) ion is consumed in a reaction, it will quickly be replaced, because the equilibrium between SO 2H 2 O, HSO 3 -, and SO 3 2- is established very fast (milliseconds), and because the dissociation of dissolved SO 2 enhances its solubility. Pathways for S(IV) to S(VI) conversion include reaction with O 3, H 2 O 2, O 2 (catalized by Mn(II) and Fe(III)), OH, NO 3,... Examples: S(IV) + O 3 S(VI) + O 2 (slow in gas-phase, rapid in aqueous-phase) HSO H 2 O 2 SO 2 OOH - + H 2 O, followed by SO 2 OOH - + H + H 2 SO 4


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