Asian Dust Cloud Information

Washington State Department of Ecology

FOR IMMEDIATE RELEASE

April 30, 1998

98-071

Contact: Larry Altose, Public Information Officer, 425-649-7192

Asian Dust Cloud Information

Ecology now considers dust from a major storm last week in China--trapped by a high pressure weather system--to be the major source of haze and elevated particulate matter air pollution levels throughout Washington and adjoining parts of North America. Reasons for this include:

Satellite photos show the dust cloud has been over our region since Sunday.
Particulate levels rose almost simultaneously at similar rates and intensity in Washington, British Columbia, Idaho, Oregon and California. The levels began going up Monday, soon after the cloud arrived Sunday.
The high particulate levels recorded are not consistent with other emissions in the region.
The dust cloud is in the lower atmosphere:
- Airplane pilot reports place the dust cloud top at 10,000 feet with clear air above. This is consistent with where the temperature inversion would be occurring within the present high pressure system that has been established over the region.
- The rate at which the cloud traveled from China to America is consistent with lower atmosphere winds.
- The dust originated at the ground.
- Heavier particles would have fallen out within several hundred miles of the source, leaving very fine matter diffused fairly evenly from the ground to the top of the inversion layer, as has been observed.

Questions and Answers:

Is it the dust cloud that has been making the sky look hazy?
Yes, and this is true in Eastern and Western Washington and in fact over much of North America this week.

Why is the dust cloud staying around so long?
The storm in Northwestern China was massive, taking lives, damaging crops and property and generating millions of tons of dust. The air mass containing the dust drifted along fairly normal patterns across the Northern Pacific and became part of a high pressure system that was becoming established over Western North America. This weather system is very stable and is not likely to move until a fairly turbulent storm develops that can break it up or move it. As a result, the dusty air mass from China is "parked" over this region for the time being.

Are the air pollution effects confined to Eastern Washington?
No. Particulate levels have trended up at monitoring stations in all parts of Washington. Our colleagues in BC, Oregon and Idaho report the same trends.

If this is affecting the whole region, why is the burn ban only in Eastern Washington?
The air pollution levels have been highest East of the Cascades. This is due to a complex set of climatological factors. The bottom line is that Eastern Washington gets less relief from stable air conditions, while the coastal parts of the state do get some low-level circulation.

How does a burn ban help the situation?
Pollution levels have been moving toward the poor air quality stage, based on national health standards for particulate air pollution. Forest slash burns and farm field fires can each contribute hundreds of additional tons of particulate matter into the air. These emissions can spread over large areas and worsen pollution levels. Even though the dust cloud is a natural event, the burn ban helps prevent a bad situation from becoming even worse.

Why not restrict other emission sources?
Legally, Ecology has authority only to control outdoor burning under the present circumstances. Some local air authorities have added temporary restrictions on indoor burning, as well.

How much dust is over Washington?
Ecology has roughly calculated the mass of dust over the state as on the order of 20 to 40 million tons.

What are some good Internet sites for more information?

Ecology's Air Program Home Page has links to several useful sites:

http://www.wa.gov/ecology/air/airhome.html

National Weather Service Seattle Forecast Office:

http://www.seawfo.noaa.gov/#clickable_map

Washington University at St. Louis has an informative page on the dust cloud episode:

http://capita.wustl.edu/Asia-FarEast/