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: “PM 10, SO 2, 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 SO 2 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 PM 10 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 (SO 2 → SO 4 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 SO 2 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 SO 2 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 SO 2 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 SO 2, 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 SO 2 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 SO 2, and hence should not create so much sulfate on the surface. This effect could be tested.

23. The End Enjoy the workshop!