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Aerosol Composition and Radiative Properties Urs Baltensperger Laboratory of Atmospheric Chemistry Paul Scherrer Institut, 5232 Villigen PSI, Switzerland WMO-BIPM Workshop Geneva, 30 March – 1 April 2010

Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

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Page 1: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Aerosol Composition and Radiative PropertiesUrs Baltensperger

Laboratory of Atmospheric ChemistryPaul Scherrer Institut, 5232 Villigen PSI, Switzerland

WMO-BIPM Workshop Geneva, 30 March – 1 April 2010

Page 2: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Aerosols particles: Solid or liquid particles suspended in the atmosphere

Examples:

Pollen: 10 - 100 m

Diesel soot: ca. 0.1 m

Ammonium sulfate: ca. 0.1 m

Sea salt: 0.2 - 10 m Mineral dust: 0.2 - 10 m

PM10 = Particles with aerodynamic diameter <10m

Page 3: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Aerosols affect our health and have an impact on climate

Source: www.ecocouncil.dk http://saga.pmel.noaa.gov/aceasia/

Page 4: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Direct and indirect aerosol effect on climate

Direct effect:Scattering and absorption of incoming sunlight by aerosol particles

Indirect effect:The number concentration of cloud condensation nuclei (CCN) influences the cloud droplet size and thereby changes the cloud albedo and lifetime

Page 5: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Indirect aerosol effect

Large dropletsWeak reflection

Small droplets Strong reflection

Indirect effectNumber of CCN influences the dropletnumber and size(Twomey-Effect) and thereby the cloudalbedo and lifetime.

Page 6: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Some of the major issues of aerosol particles• Aerosol particles have a very wide variety of sources• Many emission inventories have large uncertainties• A large fraction of aerosol mass is secondary (i.e., they are formed in the

atmosphere from gaseous precursors)• Many emission inventories of precursors have large uncertainties as well

(e.g. VOC‘s)• The aerosol yield from gaseous precursors has uncertainties of up to a

factor of 10• Impact is not only defined by mass, but also by size distribution and

morphology of particles• Short residence time (~1 week) results in high spatial variability, which

asks for many stations• Many of the components are semivolatile, resulting in measurement

issues (temperature dependence) • Aerosols cannot be packed into a bottle and sent around for certification

Page 7: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Uncertainty in the radiative forcing of black carbon (BC)

()

For comparison: CO2 forcing is 1.6 W m-2 Chung and Seinfeld (JGR 2002)

IPCC value forforcing by BC

Page 8: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

The uncertainty in the aerosol forcingis a major reason for our limited

understanding of the total radiative forcing

IPCC (2007)

Page 9: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

WMO GAW SAG:Scientific Advisory Group For Aerosols

Continuous Measurement 1. Multiwavelength optical depth 2. Mass in two size fractions 3. Major chemical components in two size fractions 4. Light absorption coefficient 5. Light scattering coefficient at various wavelengths 6. Hemispheric backscattering coefficient at various

wavelengths 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation

Intermittent Measurement 1. Aerosol size distribution 2. Detailed size fractionated chemical composition 3. Dependence on relative humidity 4. CCN spectra (various supersaturations) 5. Vertical distribution of aerosol properties

GAW Report # 153. WMO/GAW Aerosol Measurement procedures guidelines and recommendations (September 2003)

List of comprehensive aerosol measurements with a subset of core variables (identified in bold) that are recommended by the GAW Scientific Advisory Group on Aerosols for long-term measurements in the global network.ftp://ftp.wmo.int/Documents/PublicWeb/arep/gaw/gaw153.pdf

Page 10: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

In an ideal world

• There is an agreed method• Instruments of different institutions have successfully

been intercompared• There is a hierarchy of standards

Page 11: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

In an ideal world

• There is an agreed method• Instruments of different institutions have successfully

been intercompared• There is a hierarchy of standards

The ideal world does not exist for any of the aerosolvariables

Page 12: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Closest to the ideal world: Aerosol optical depth(i.e., aerosol extinction coefficient integrated over full column)

Aeronet

Different instruments,Different calibrationprocedures, but:AOD usually showsexcellent agreementbetween proper instrumentsCan also be measuredfrom satellites

Plus many othernational networks(Russia, ……)

Page 13: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

A WMO/GAW Experts Workshop“A Global Surface-Based Network for Long Term Observations of

Column Aerosol Optical Properties”March 2004, WORCC Davos, GAW Report # 162

ftp://ftp.wmo.int/Documents/PublicWeb/arep/gaw/gaw162.pdf

There is still a lack of coordination between networks, but there is an agreement for further harmonization under the lead of the SAG

Page 14: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Vertical profiles

In addition:- MPLNET, a global network

- Satellites

Different instruments, different procedures, much less agreementbetween data than for AOD

Page 15: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Distribution of stations

ALINE, Latin America

AD-Net, East Asia

CIS-LINET, Commonwealth of Independent States

EARLINET, Europe

NDACC, Global Stratosphere

REALM, Eastern North America

MPLNET, Global, Micropulse Lidar

Page 16: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Plan for the implementation of the GAW Aerosol Lidar Observation Network

GALION, WMO/GAW Report No. 178http://www.wmo.int/pages/prog/arep/gaw/documents/gaw178-galion-27-Oct.pdf

Page 17: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

PM10, PM2.5 and/or PM1 and chemistryLargely separated networks, Within individual networks: regular quality control, but mostly no formally established intercomparison between networks

EUSAAR

Page 18: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

The worst of all possible situations:Organic and elemental carbon

Schmid et al., 2001: Factor of 10 difference between individual methods;Today: Factor of ~2

Until recently two competingprocedures in the US, from whichthe IMPROVE procedure survived

Today, intercomparison betweenIMPROVE, ENV-CANADA and EUSAAR (Europe): still large discrepancies.

We do not even have decent reference samples: reference material NIST 8785 was shown to have drifts and inhomogeneities in their samples.

A possible way out: use advanced optical methods (e.g., SP2) to determineblack carbon, rather than chemical determination of EC.

Page 19: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

More promising:Physical and optical properties

‘Advantage‘: no established network when SAG started in 1997 (except NOAA) Adoption of guidelines by SAG (GAW Report # 153, 2003) by most stationsFurther development involved all major players, under the lead of the Aerosol SAG (ftp://ftp.wmo.int/Documents/PublicWeb/arep/gaw/gaw153.pdf)

Page 20: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

EUSAAR: a Blueprint for harmonizationExample: Stations reporting physical or optical properties inEurope:

in 2002 in 2008

Stations are using the same protocol,Instruments are regularly intercompared,Data are stored in agreed format in World Data Center for Aerosols,Some recommendations were transferred to the German UBA, the German DWD, and to the British National Physical Laboratory, NPL

Page 21: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Long-term trends are becoming possibleExample: Jungfraujoch, Switzerland, 3580 m asl

10 years of data are necessary

June - August: no significant trend ofbs, babs, and CN

September - December: significant positive trend of 2 - 4% per year (for bs, babs, and CN)

Collaud-Coen et al. JGR 2007

Page 22: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Capacity building is an important issue

• On-site audits (mainly done by World Calibration Center for Aerosol Physics)

• Instrument intercomparisons• Traveling standards (size distribution, PFR for AOD

measurement)• Training courses• Twinning activities

Page 23: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Towards an integrated aerosol approach

Page 24: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

An important issue for this integrationin situ variables are measured ‘dry‘ (<40%RH),

for comparison e.g. with satellite products these need to beconverted to ambient conditions

Example: Enhancement of scattering coefficient with increasing RH

Page 25: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Summary

• Aerosol observations have made great progress in the last decade, in method development, standardization, harmonization between networks, capacity building, and data availability (at new World data center for aerosols, http://ebas.nilu.no/

• Challenges remain, in all above aspects• We need to work together towards an Integrated observing

system building on satellite, ground-based remote sensing and in situ data

Page 26: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Where could BIPM contribute?

• Formulating SOPs• Supporting intercomparisons• Providing suitable reference maetrials• Develop standards for aerosol number concentration• Develop standards for sampling inlets and sample

conditioning• Transferring knowledge to instrument manufacturers etc.• ….• A representative of BIPM in the Aerosol SAG could be useful

Page 27: Aerosol Composition and Radiative Properties · 7. Aerosol number concentration 8. Cloud condensation nuclei at 0.5% supersaturation Intermittent Measurement 1. Aerosol size distribution

Thank you for your attention