The First Meeting of the Dust Club

1. The First Meeting of the Dust Club 4–5 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 don’t understand. • Don’t 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 storms—adsorption 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 Jinghua’s 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, cont’d • 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, cont’d • 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→ SO4in 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 happen—the 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 don’t coagulate with coarse particles. • Coarse particles don’t 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, cont’d • Maybe it is related to the humidity of the air—low 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!