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EPA \ TAQMN \ Dust Storm

Dust Storm

The Occurrence and Effects of Dust Storm

Aside from being affected by fixed pollution sources (factories, industrial areas) and moving pollution sources (scooters and automobiles), the air quality in Taiwan is also severely affected by factors from foreign areas, mainly from China. These sources are both man-made and from natural environments. From the results of Taiwan's annual air quality, we can see the degree to which foreign pollution affects Taiwan.

On the morning of March 24th, 2000, Taiwan was affected by dust storm originating in China. The result was poor air quality, and as dust storm continued to occur in China, Taiwan's air quality continued to suffer until April 1st, at which point rain in Taiwan caused air quality to finally improve. The affected area and duration of this dust storm was rarely seen in previous years. Since the air quality monitoring network was completed in 1993, Taiwan's analytical ability of pollution sources has greatly improved, especially in cases where foreign air pollution invades Taiwan. This instance of Chinese dust storm has severely affected Taiwan's air quality, and the Environmental Protection Administration has been carefully watching the situation to provide the general public appropriate warning to ensure their health. Below is a description of the characteristics of East Asian dust storm.

1. The source and climate conditions of east Asian dust storm

The desert regions of northwest China totals nearly 600,000 square km and is mainly located at latitude 35 degrees north and longitude 125 degrees west in the regions of northern and western China along with the Mongolian region, which includes Xinjiang, Gansu, Hetao, inner Mongolia, Mongolia, and other regions. The annual rain fall in this region is consistently below 400mm and seasonal division is highly uneven. This is the main source of dust storm that occurs in East Asia. Winter and spring seasons are the main periods when dust storm occurs, especially from the months of March to May which account for 60% of dust storm per year. The numbers of dust storm that occur annually are not uniform.

Studies show that sand from desert regions are the main source of suspended particles on the planet. The Sahara Desert itself accounts for 25% of the suspended micro particles in the atmosphere (Zhao and Yu, 1990). Northwest China resides in the desert region of central Asia which is the runner up in the four major desert regions in the world (ranking is central Africa, central Asia, north America, and Australia); therefore, the influence of northwestern China's desert region greatly impacts the atmospheric environment of east Asia. The conditions for dust storm are:

  • Geographical Conditions: Loose, dry dirt with no vegetation and no snow.
  • Climate Conditions: Strong winds on the ground, vertical and unstable weather conditions and the lack of rain or snow fall.

2. The Global Effect of Dust Storm

After large dust storm occur in winter and spring, the sand blown up causes the atmosphere to be filled with large amounts of sand, obstructing sunlight and at time reducing visibility to zero, which is why super dust storm are also called black storms. According to studies, there have been 48 super dust storms in the northwestern region of China in the past 40 years, causing 11 deaths and great damage to the lives and agriculture industry of the people. Taiwan is not a main region of transport after super dust storm occur in China, only under special weather conditions will it lead to poor air quality. The mud rain phenomena of March 12th and 13th of 1995 are the most severe cases.

Larger particles usually affect the source or neighboring areas after a dust storm, then return to the earth; smaller particles of sand are transported upwards of 850-700 hPa which is approximately 1000-3000 meters, then carried by the west wind belt to the east. During transportation, a portion may be dispersed or diluted causing the transportation distances to be even further; the lower density is caused in part by snow or rain fall which bring the particles back to earth. When moving east, the dust storm of northwestern China can affect Japan, Korea, or even Hawaii which is 10000 km away. They can also affect southern neighbors such as Taiwan, Hong Kong, or even the Philippines; apparently, the affected areas are very wide.

Dust storm that are transported several thousand kilometers to other regions often affect local visibility and causes suspended particles in the atmosphere to increase, affecting local air quality. The duration and scale of affect is usually determined by the scale and duration of the original dust storm coupled with whether local weather conditions are advantageous to the transportation or settlement of sand. According to past records, visibility may be affected for a few hours or muddy rain phenomenons can occur when duration is a week. Therefore, countries that are affected by dust storm monitor weather and air quality to under the affected conditions of local regions, then retroactively study the time of occurrence and scale of the original dust storm.

As dust storm occur in desert regions where the earth is loose, dry, and without vegetation, when the air is unstable in the greater region and ground wind speed is very high, sand is easily blown from the ground into the air to form dust storm. In recent years the desertification of China's northwest region has become more severe causing the frequency and scale of dust storm to increase. This is a problem that must be swiftly addressed to prevent the occurrence of dust storm.

3. The Environmental Protection Administration's Monitoring and Measures for Dust Storm

Dust storm usually need 24 to 36 hours from their time of occurrence in China to affect Taiwan, meaning there is ample time to collect related information. The EPA assesses atmospheric conditions to determine whether dust storm will affect Taiwan as a part of their daily dust storm forecast. Currently, information related to the development of dust storm is determined by the EPA through the methods below:

  • Routine weather reports: According to current regulations of the World Meteorological Organization, international weather stations must announce weather conditions every 3 hours (at 2 AM, 5 AM, 8 AM, 11 AM, and 2 PM, 5 PM, 8 PM, 11 PM). From this information a complete ground weather report can be formed for the east Asia region to determine the strength and scale of dust storm.
  • Observing weather conditions: As east Asian dust storm mainly originate from latitude 35 degrees north and longitude 125 degrees west in the regions of northern and western China along with the Mongolian region, when dust storm occur fine particles of sand are lifted 1000 to 3000 meters into the air and transported east by the west wind to Korea and Japan through Beijing without directly affecting Taiwan. Therefore, observing China's cold front system to determine whether it is advantageous to the transportation of sand is important to assess whether it will affect Taiwan, or lower latitudes.
  • Satellite weather imaging data: A more complete grasp of a dust storm's affected areas can be obtained by using MODIS satellite images to determine the position of dust storm to use along with ground weather reports to see "gray" shadows where dust storm occur. However, this method is restricted by the fact that dust storm must occur in regions with less clouds, and if there are clouds in the path of the dust storm it will become difficult to determine the dust storm's position. Therefore, when east Asian dust storm travel from their point of origin to the eastern sea, it often causes problems in identifying them.
  • Air quality monitoring data: According to historical reports on Taiwan's air quality and related studies, dust storm are transported to Taiwan through China's cold front by the northeastern seasonal winds which is why the EPA has assigned the coastal monitoring stations of Wanli, Guanyin, Yilan, and even the Yang Ming National Park monitoring station to determine the affect of foreign pollutants. The average suspended particle density of these stations are mostly unaffected by local pollution, with micro particle density mostly below 50 micrograms per cubic meter. When these stations are affected by foreign pollutants, their particle density rapidly increases to more than 100 micrograms per cubic meter. This increase in density has characteristics of increasing from north to south, from coastal regions to in land regions. The EPA has established an automatic computerized monitoring system to immediately report related information when the conditions described above occur.

Dust storm are a highly active weather phenomenon in the east Asia desert regions during winter and spring and those that are transported long distances only account for a small portion. Those that can affect Taiwan's air quality are even less, but as they can cause Taiwan's air quality to deteriorate, the EPA has put a considerate amount of importance in this matter. In order to strengthen the certification of long distance transported pollutants, the EPA established the Matsu monitoring station in 1999 to better quickly grasp when dust storm will affect Taiwan. According to this year's monitoring results, when the Matsu station detects an increase of micro particle density due to dust storm, Taiwan is affected in a few hours.

 

last update : 2017/07/31

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