The Asian Dust Event of April 1998 A preliminary report prepared by an Ad Hoc Virtual Workgroup May 11, 1998 Draft - Please use the Feedback page for commentsFeedback

This preliminary account of the extreme Asian dust event of April 1998 is the result of a collaboration (sharing of resources) by a virtual web- based community that was created spontaneously during the dust event. The shared workspace of the community was the Dust Event website, Virtually all of the forty registered and many non-registered participants have contributed observations, monitoring data, interpretation or helped the creation of the virtual community. The institutions of the participants included state air quality management agencies, government laboratories, universities, and private citizens. This is an evolving document, subject to changes based on the feedback from the community.feedback

The Dust Storm in Western China and its Transport Across the Pacific Ocean

On April 15th, 1998 an unusually intense dust storm began in the western Chinese Province of Xinjiang, just in time for the east Asian dust season. CNN reported that 12 people were missing from that singular event. Area Map of Xinjiang ProvinceCNN Video Clip of Dust Storm

On April 16th, routine examination by Washington University of SeaWiFS satellite images first detected a distinct yellow dust cloud over central China. SeaWiFS SeaWiFS Image of Dust Cloud over China on April 16 Animation of the Dust Cloud from GMS-5 (Geostationary Satellite on April 19

On April 19th another dust front moved across China. By April 20th, the elongated dust cloud covered a 1000 mile stretch of the east coast of China. The Chinese Academy of Sciences reported a yellow rain in Beijing. SeaWiFS Image of Dust Cloud on April 19SeaWiFS Image of Elongated Cloud on April 20

On April 23rd and 24th, the dust storm was rapidly moving across the Pacific Ocean. The dust cloud appeared as a yellow dye and visualized its own path across the Pacific. Approximate path of the dust cloud as it transited the Pacific Ocean SeaWiFS Image of Cloud Approaching North America on April 24

During the trans-Pacific transit the dust plume was also tracked independently by Washington University and University of Wisconsin using GMS-5 and GOES-9 geostationary satellites, respectively.University of WisconsinGOES-9 geostationary GMS-5 Image of Dust over the Central Pacific on April 24 GOES-9 images of Dust over the Central Pacific on April 24

Observations of the Asian Dust Event Over the Pacific Coast of North America

By April 27th, the dust cloud rolled into North America. Goes-10 and SeaWiFS images indicate that the dust plume split once it reached land - one branch heading southward along the California coast and another branch continued eastward across the Canadian Rockies.Goes-10 SeaWiFS GOES-10 Image of Dust Cloud on April 27SeaWiFS Image of Dust Cloud on April 27

The normally blue sky was observed to be notably milky and washed out over much of the West on April 27th. University of Nevada monitored the aerosol optical depth prior and during the event.University of Nevada Milky Appearance of Sky at Sunset in Reno on April 27 Aerosol Optical Depth Monitoring at Reno Show AOT in Excess of 0.5 During Dust Event

By serendipity, the size distribution of the Asian dust was measured by the University of Washington aircraft. The State of Washington Dept. of Ecology conducted routine monitoring of PM10 and PM2.5 concentrations. University of Washington Size distribution data of the dust indicate that most of the mass is above 2.5umin diameter. Surface based monitoring of PM10 and PM2.5 indicates that during the dust event 2/3 of the PM10 mass was above 2.5um

LIDAR aerosol data by the Jet Propulsion Laboratory reveals that height of the dust layer on April 27 at Pasadena, CA was in the range of km above sea level.Jet Propulsion Laboratory

Air Quality Management Activities

The Activities of AQ Management Agencies Based on public complaints and monitoring data, the State of Washington Department of Ecology issued a ban on open burning on April 29th. On April 29th, the ‘PM alarm’ went off at several continuous monitoring stations around Vancouver, BC, because the concentration exceeded 50 ug/m3. The British Columbia Ministry of the Environment has investigated the underlying causes of the particulate matter event. California Air Resources Board scientist have explored whether the cause of the high PM10 concentrations (. 50ug/m3) at many sites could be attributed to large prescribed burns in Oregon, Idaho, and Washington. At the South Coast Air Quality Management District in Los Angeles, reduced visibility and elevated PM10 measurements were initially attributed to large scale prescribed burns in Idaho and later to the Asian dust. United States Department of Agriculture - Forest Service in Idaho was concerned about intense haze around Salmon and Challis National Forests and the possibility of smoke impact from prescribed fires. By April 29th, the Idaho Department of Environmental Quality has advised that the haze may be due to the Asian dust event.

The Role of the Virtual Community Virtually all the Air Quality management agencies have participated in creating an instant virtual community and have benefited from the information resources on the Website in making their quick decisions. On April 30, the State has issued an explanation to the public that “…now seems fairly certain that the Eastern Washington air stagnation event is due mostly to Chinese dust rather than locally generated pollutants”. In the press release, the Dust Event Website address was given to the public for further information on the event. It could be said that the community and its shared web resources have contributed certain amount of JITERS (Just In Time Environmentally Relevant Science) to the AQ managers. Evidently, the trust of the managers in the available science support arose from the multiplicity of independent observations, and from weight of the evidence. (Managers, is this true?)

Acknowledgements Anderson, T. Arimoto, R. Bachmeier, s. Brock, C. Chavez, P. Conel, J. Dubois, D. Durkee, K. Falke, S. Gasso’, S. Gill, T. Hansen, T. Helmlinger, M. Hennessey, J. Holben, B. Huebert, B. Husar, R. Husar, M. Jackson, G. Jaffe, D. Johnson, B. Juric, S. Li, F. Lyle, K. Lyons, W. Merrill, J. Miller, R. Mims, F. Porter, J. Redmond, K. Reheis, M. Reynolds, R. Rogers, W. Sakiyama, S. Schichtel, B. Schnell, R. Tratt, D Van Hook, B. VanArsdale, A. …and many others