The First Meeting of the Dust Club

1
The First Meeting of the Dust Club

• 45 April 2005
• SEPA, Beijing

2
Welcome!
3
Goals of the Dust Club

• Bring like-minded scientists together for regular
  discussions.
• Provide a friendly, relaxed environment for
  friends to meet.
• Promote free and open exchange of information and
  ideas on dust storms.
• Promote dust-storm research.
• Stimulate collaborative research.

4
Goals of This First Meeting

• Allow dust-storm scientists in Beijing to get
  better acquainted.
• Bring each other up to date on recent research.
• Introduce students to the field.
• Discuss new findings.
• Address new problems.
• Search for clear answers.

5
Overview of Sessions

• Monday morning Sources and Transport
• Monday afternoon Areas of contention effects
  and mitigation
• Tuesday Planning cooperative research

6
Topics to Consider

• History of dust storms.
• Sources of dust storms
• From surface networks
• From meteorology
• From chemistry
• From satellites
• Transport
• From surface networks
• From meteorology
• From chemistry
• From satellites
• Mitigation
• Areas of current debate
• Gaps in knowledge
• Next steps
• Potential collaboration

7
Speakers

• Zhang Kebin, Beijing Forestry Univ. Dust storms
  and desertification.
• Gao Qingxian, SEPA General comments on
  dust-storm research.
• Gao Xiang, Fudan U. Dust storms in Tibet.
• Zhao Linna, Nat. Meteor. Ctr., CMA Integrated
  dust storm numerical system and its application.
• Zhang Shihuang, Inst. of Geog. Sci. and Nat. Res.
  Resarch Fluctation of desertification of China
  and Mongolia from the fraction of vegetation
  cover.
• Kenneth A. Rahn, BNU New chemical information
  on sources of dust storms.
• Guo Jinghua, BNU PM10, SO2, and dust storms.
• Cai Xuhui, PKU Numerical simulation of dust
  particle dispersion from surface to the
  atmosphere
• Zhang Xiaoling, Beijing Inst. of Urban Meteor.,
  CMA Dust weather in Beijing and model
  simulations.
• Shi Zongbo, TU The chemical and mineralogical
  compositions of Asian dust-storm particles.

8
Suggestions for Speakers

• Omit introductory material that everybody knows.
• Go directly to the new material of greatest
  interest.
• Present the findings, their possible
  explanations, and their implications.
• Keep the explanations simple.
• Allow plenty of time for discussion.
• Do not worry about vigorous give-and-take.

9
Suggestions for the Audience

• Question everything that you dont understand.
• Dont be afraid to interrupt the presentations.
• Express your open and honest opinions.
• Try to be constructive and helpful.

10
Some Areas of Current Debate

• Adequacy of surface observational networks.
• Small-scale sources of dust storms?
• Chemistry vs. meteorology
• Pollution storms?
• Sources of S in dust stormsadsorption of
  pollution SO2 or just mineral sulfate?
• Mixing with pollution during transport.
• Temporal trends in dust storms.
• Human desertification vs. climatic changes.
• Effectiveness of mitigation measures.

11
Adequacy of surface observational networks

• Many conclusions about the origins of dust storms
  are based on the appearance of dust at
  meteorological observation stations.
• Guo Jinghuas daily maps of PM10 during dust
  storms reveal that dust storms jump around both
  near the source and far from it.
• This seems to indicate that stations are missing
  in critical places.

12
Are critical stations missing?

• Prospero (2002) has noted that stations are often
  sited by practical considerations.
• They tend to be near cities or towns, not in
  barren areas.
• Dust near cities can be influenced by urban
  activities such as roads and traffic.
• The real sources of dust may be outside the
  cities.
• They may also be small-scale hot spots that are
  still incompletely understood, especially in
  Chinese deserts.

13
Hot spots

• Deserts are not uniform sources of dust.
• SeaWiFS observations in Africa and the Gobi
  reveal that large dust clouds begin as multiple
  small plumes from hot spots, then diffuse into
  larger clouds.
• These hot spots are often fixed places that
  reappear regularly.
• They are commonly local depressions that
  accumulate fresh soil or salt.

14
Hot spots, contd

• They can be dried lake beds, ephemeral river
  channels (wadis), or entire basins.
• Their common feature is fresh fine-grained soil.
• This soil often comes from nearby mountains or
  hills, via rivers that drain into the depressions
  and evaporate.
• This makes the fresh soil salty.

15
Hot spots, contd

• The chemical composition of the fine soil can
  differ from that of the older surrounding soil.
• This could make desert dust differ from the
  deserts as a whole.
• Hot spots in the Gobi and the Takla Makan should
  be identified and studied.
• They may explain the chemical signatures of the
  two important sources.

16
Pollution storms?

• Are dust storms also pollution storms?
• We have heard this idea proposed lately.
• If dust storms mean unusually high
  concentrations of dust, pollution storms must
  mean unusually high concentrations of pollutants.

17
Mechanisms for pollution storms

• Only two that I can think of
• (1) Resuspension of contaminated soils during
  dust storms.
• This would produce coarse-particle pollutants.
• Wind speeds usually too low, especially for
  floating dust or falling dust.
• (2) Adsorption of pollution gases to surfaces of
  dust particles (SO2 ? SO4 in particular).
• This rate is too slow in the dry, cold air of
  dust storms.
• Not enough time within Beijing (2 hours?).
• Could work if the SO2 was introduced early, say
  over Lanzhou.
• But no real evidence for this process.

18
Mechanisms for pollution storms

• No other mechanism to enrich primary pollutants
  in dust-storm aerosol.
• In fact, the opposite should happenthe northern
  air with the dust should contain minimal
  pollution.
• That is what most of the data show.
• The idea of pollution storms appears to have
  originated with a single flawed data point in a
  dust storm from 2000.
• It is time to let pollution storms die.

19
Mixing of dust and pollution during transport

• As dust is transported, its air mass will pick up
  pollutants.
• This is especially true for air near the surface.
• The air without the dust would have picked up the
  same amount of pollution.
• The pollution particles will not coagulate much
  with the dust particles, however
• Fine particles dont coagulate with coarse
  particles.
• Coarse particles dont coagulate with other
  coarse particles.
• But the pollution aerosol will travel with the
  dust aerosol.

20
The importance of dust signatures

• Allows the sources of dust to be distinguished.
• Allows the effects of added pollution to be
  identified.
• This can say something about the trajectory and
  the altitude of transport.

21
Adsorption of SO2 on dust particles

• Several articles show that most dust particles in
  Japan and Korea are coated with sulfate and
  nitrate.
• BUT, Zhang et al. (2003) have shown that only a
  small fraction of dust-storm particles at Qingdao
  are coated in this way.
• Song et al. (2005) found similar results for dust
  particles off Qingdao.
• This result is consistent with the known slow
  rates of conversion of SO2 to sulfate on surfaces
  of dust (several days required for full
  conversion).
• BUT, why is there such a difference in the
  coatings over such a short distance?

22
Adsorption of SO2, contd

• Maybe it is related to the humidity of the
  airlow over the continent but higher over the
  water.
• Particles over the sea may quickly develop a thin
  coating of water into which the SO2 can dissolve
  and become oxidized.
• But this should happen only near the sea surface.
• Dust above the marine boundary layer should not
  adsorb so much water and SO2, and hence should
  not create so much sulfate on the surface.
• This effect could be tested.

23
The End

• Enjoy the workshop!