AEROSOLPROZESSE 1. Sichtbare Bedeutung von Aerosolkonzentrationen 2 PM2.5 levels of 5 μg/m3 (left)...

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AEROSOLPROZESSE 1

Transcript of AEROSOLPROZESSE 1. Sichtbare Bedeutung von Aerosolkonzentrationen 2 PM2.5 levels of 5 μg/m3 (left)...

Page 1: 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.

AEROSOLPROZESSE

1

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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 100-110 micrograms per cubic meter of air in the year of 2000 to 70-80 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

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Definitions

Aerosol: suspension of fine solid or liquid particles in a gas

primary aerosol: emitted directly as particlessecondary aerosol: formed in the atmosphere by gas-to-

particle conversion

fine aerosol: particles < 2.5 µmcoarse aerosol: particles > 2.5 µm

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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)

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Chemical composition

Tropospheric aerosol contains:• sulfate• ammonium• nitrate• sodium• chloride• trace metals• carbonaceous material• crustal elements• water

Urban aerosol composition

C (elem)

C (org)

NH4(+)

NO3(-)

SO4(2-)

Rest

after Seinfeld&Pandis, 1998

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Chemical composition (2)

6http://www.esrl.noaa.gov/research/themes/aerosols/

Schiffbasierte Messungen von Aerosolen in verschiedenen Weltregionen

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Chemical composition (3)

7Mayol-Bocero, 2000

Filterproben aus Messflügen über dem Indischen Ozean

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Aerosoltypen und Größenverteilung

8Heintzenberg et al., in „Atmospheric Chemistry in a Changing World“, Springer, 2003

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Aerosol size distribution

Consider only spherical shape ...

number density distribution

surface distribution

volume distribution

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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 0.1-0.5%; minimum particle diameter is 50-140 nm

• CCN number concentrations: < 100 cm-3 in remote marine areas to > 10000 cm-3 in polluted areas

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Cloud condensation

Liquid Water Content (LWC): L = 0.05-3 gH2O/m3

Droplet size: r = 1 µm - 50 µm

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Bedeutung von Aerosolen: Strahlung

13

Direkter Effekt

Indirekte Effekte

http://www.wmo.int/pages/prog/arep/gaw/aerosol.html

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14http://www.gfdl.noaa.gov/atmospheric-physics-and-chemistry_aerosol_cloud

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Processes simulated in an atmospheric chemistry transport model

15

Gas photochemistryGas-to-particle conversion

Gas processes

Optical depth of gases/ aerosols/cloud dropsSolar radiative transferInfrared radiative transfer(Visibility)

Radiative processes

NucleationCoagulationCondensation/evaporationDissolution/evaporationDeposition/sublimation

Freezing/meltingReversible chemistryIrreversible chemistryHeterogeneous chemistry

Aerosol/cloud processes

Wind speed & directionAir pressureAir densityAir temperatureSoil temperature & humidityTurbulence…

Dynamical/thermodynamical processes

EmissionsTransport of gases/aerosols/ cloud drops/energyDry deposition of gases/ aerosols/cloud dropsSedimentation of aerosols/ cloud drops/rain drops

Transport processes

nach

Jac

obso

n, 1

999

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Sources of aerosol (emissions)

• windborne dust• sea spray• volcanoes• fossil fuel combustion• road transport• pollen and plant fragments

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Nucelation – Coagulation - Condensation

17http://www.realclimate.org/images/aerosol1.jpg

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Nucleation

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

Cluster Particles

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

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Absorption equilibrium

A(g) A(aq)

for dilute solutions:[A(aq)] = HA · pA

aqueous-phaseconcentration(mol L-1)

Henry coefficient(mol L-1 atm-1)

partial pressure ofA in gas-phase(atm)

Gas/Aqueous phase partitioning

LTRHc

cf A

g

aqA 610

Aaq fx

1

1

solu

ble

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Gas/Aqueous-phase partitioning

very soluble gases: H2O2, HNO3, NO3

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Coagulation

22http://www.chm.bris.ac.uk/pt/aerosol.htm

Beobachtung des Zusammenwachsens von Wolkentropfen mit gepulster Laserspektroskopie

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Aerosol processes in clouds

23C. Hoose et al., 2008

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Condensation / Evaporation

24

Modelliertes Wolkentröpfchenmit Sulfatmolekülen als Kondensationskeimen

http://www.pnl.gov/science/highlights/highlight.asp?id=976

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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).

http://www.tlc2.uh.edu/uhaero/Applications/ImageGallery/acp9b/view

Ammonium/Nitrate/Sulfate30% SO4, T=298 K

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Modellierung von Aerosolen

26

• Bulk-Schema• Bin-Schema• Modales Schema

• Interne Mischung• Externe Mischung

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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

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Comparison bin and modal scheme

28K. Carslaw and D. Spracklen, U. Leeds

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Concept of M7 (modal aerosol model)

29E. Zubler, ETH-Zürich

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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 N1, MSO4

5 N5, MBC, MOC

6 N6, MDU

7 N7, MDU

2 N2, MSO4, MBC, MOC

3 N3, MSO4, MBC, MOC , MSS , MDU

4 N4, MSO4, MBC, MOC , MSS , MDU

NUCLEATION(r < 0.005 µm)

MODES IN M7

Aerosol Representation in ECHAM-HAMMOZ

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Aerosol Mixing State

P. Stier, U. Oxford

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Evaluation of ECHAM6-HAMMOZ

32

Jan

Jul

AOD @ 550 nm

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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

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Global SO2/SO4 annual budgetecham6-hammozunits: Tg (S)

SO4 gas

SO2 SO4 aero

2.3

4.921.8

15.5

6.0 19.2

690.047 0.032

1.7

1.5 59.1 2.2

43.1

23.80.23

DMS-OH

DMS-OHDMS-NO3

SO2-OH

wetdep drydepemi

wetdep drydep wetdep drydepsedi

emi

condensationnucleation

wetchemistry

G. Frontoso, ETH-Zürich

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Multi-Modell Vergleich (AEROCOM)

35

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Ruß (Black carbon)

36

Ruß entsteht bei der unvollständigen Verbrennung von fossilen Brennstoffen, Holz oder Kohle

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EXTRA MATERIAL

37

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pH

Upon dissolution in water, several species will form ions, e.g. H2O, and CO2.Water:H2O H+ + OH- ; equilibrium constant K = [H+][OH-](at 298K, only 2 µmol/L ions versus 55.5 mol/L H2O)

pH = -log10[H+]

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Dissolution

Generally: K = [X+][Y-] / [X•Y]

TABLE6.4

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CO2 uptake by the oceans

CO2(g)

CO2•H2OCO2(aq) = H+ + HCO3-

Kc1

H+ + CO32-

Kc2

carbonate bicarbonate

Khc

2

2

CO

22CO

OHCO

pHKhc

OHCO

HCOH

22

-3

1

cK

-3

-23

2 HCO

COH

cK

total dissolved carbon:

22 CO2211

CO

-23

-322

HH1

COHCOOHCO

pKKK

H ccc

effective Henry coefficient

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CO2 uptake by the oceans (2)

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SO2 uptake by droplets

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Acidity of (clean) rainwater

This can be rearranged to:

The atmospheric CO2 concentration has an influence on theacidity of rain water:Electro neutrality demands that

-23-3 COHCOOHH

2CO21COCO1COOH

H

2

HHH 22222

pKKHpKHK ccc

With given temperature and pCO2, [H+] can be computed, fromwhich all other ion concentrations can be deduced.For T=298K and pCO2 = 350 ppm, pH = 5.6

Other species of interest: SO2 HSO3- SO3

2-, NH3 NH4+, HNO3 NO3

-

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S(IV) S(VI) oxidation

The conversion of dissolved SO2 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 SO2•H2O, HSO3

-, and SO32- is

established very fast (milliseconds), and because the dissociation of dissolved SO2 enhances its solubility.

Pathways for S(IV) to S(VI) conversion include reaction with O3, H2O2, O2 (catalized by Mn(II) and Fe(III)), OH, NO3, ...

Examples: S(IV) + O3 S(VI) + O2 (slow in gas-phase, rapid in aqueous-phase)

HSO3- + H2O2 SO2OOH- + H2O , followed by

SO2OOH- + H+ H2SO4