History of dust storm monitoring
On March 12, 1995, many citizens reported to environmental protection authority, saying that their cars were covered in a layer of reddish-brown mud powder and the water ponds on roadsides had reddish-brown slurry after a rain in Northern Taiwan, including Keelung, Yilan, Xizhi, and Ruifang. Some people speculated that the mud was spattered because of passing mining dump trucks or some intentional mischief, and some people thought it was caused by pollution from Taipower's Hsieh-ho Power Plant. The newspaper reported that the official vehicle of Liao Hsueh-Kuang, the head of Xizhi then, was also covered by mud in the afternoon on that day. For some time it was thought to be a hostile gesture caused by opponents. Neither environmental protection nor meteorological authorities could provide a reasonable explanation to the cause of the "red muddy rain." Later, with the assistance of several experts in environmental engineering and meteorology, the EPA found that the red muddy rain might caused by a long-range transport of dust storm originated from East Asia (such as mainland China and Mongolia). Since then, people started to pay more attention to how the dust storms in East Asia might affect air quality in Taiwan.
Dust storm is a very active weather phenomenon in desserts of East Asia in spring. Dust storms that travel a long distance are only a small part of the dust storm phenomenon every year, so the chance of them causing serious influence on air quality in Taiwan is low. But when they do hit, they hit hard, causing air quality in Taiwan to deteriorate at a large scale in a short period time, so the EPA attaches great importance on them. To validate the causal relation between the dust storms traveled from afar and the pollution in Taiwan, EPA has been conducting related studies, and established a monitoring station in Matsu since 1999, so to know better about when dust storms might affect Taiwan ahead of time. According to the observation in some cases, it was found that when the concentration of suspended particulates at Matsu station rises because of the dust storms, Taiwan island can be affected in several hours.
Dust storms mostly occur in desertification areas, where the soil is soft and the surface is dry and without vegetation. Therefore, when the air in a larger space is unstable and the surface wind speed is strong, the wind can easily lift the dust on the surface into the air and form a dust storm. In recent years, the desertification in Northwestern China is becoming more serious, leading to stronger and more frequent dust storms. Taiwan might continue to be affected by them in the future, unless mainland China can resolve the desertification problem to prevent dust storms from happening.
Formation of Dust Storm
Read data to predict behaviors of dust storms
To determine whether a dust storm will affect Taiwan's air quality, the EPA collected and organized data on paths by which dust storms hit Taiwan in the past, including atmospheric conditions and air quality during dust storms, and established the following procedure to determine whether a dust storm would affect air quality in Taiwan.：
Determine whether there is a dust storm in East Asia
The determination is mostly based on an analysis of regular weather reports.According to current regulations of the World Meteorological Organization (WMO), international weather stations must announce weather conditions every 3 or 6 hours (at 2 AM, 5 AM...8 PM, and 11 PM). Therefore, with a more comprehensive ground weather report of East Asia region, we can determine the strength, scale and area to be affected of a dust storm.
During the time period when dust storms are active (November to May next year), weather forecasters at EPA access WINS, a system of Central Weather Bureau that provides data to the EPA, at 9AM every day to read weather reports published by weather stations in East Asia every 3 hours. With these reports, they can determine whether there was a dust storm in Northwest and North China and Mongolia from 5AM yesterday until 8AM today.
Mainland China has established a web page on dust storm in China. Thanks to the convenience of the internet, forecasters can access this web page to examine observations, forecasts and related reports concerning dust storms, in addition to the aforementioned meteorological data, to determine whether a dust storm is coming. In recent years, environmental protection authorities in different areas of mainland China continue to establish air quality monitoring stations. Therefore, the analysis of the strength, transport paths and influence of dust storms can also include air quality monitoring data of each city in mainland China collected and organized by the Ministry of Ecology and Environment, China.
Evaluate the probability of dust storms transporting to Taiwan
After it is confirmed that a dust storm has been formed in Mongolia or mainland China, we need to closely observe whether it is going to affect Taiwan by paying attention to a variety of meteorological conditions. The main source region of dust storms in East Asia is north of 35 degree North latitude and west of 125 degree East longitude, mostly Northwest and North China, and Mongolia. When a dust storm occurs, fine aeolian dusts are raised 3000 meters into the air and sent eastward along with the west wind, normally from Beijing in mainland China to Korea and Japan, and usually do not affect Taiwan directly. Therefore, the meteorological conditions we need to observe include the North-South cold high-pressure system in mainland China, which is conducive to a shift of the travel direction of the dust, originally west-to-east at an upper atmospheric level, to a southward transport along with the northeast monsoon prevail at a lower height. Thus the dust storm will affect Taiwan or even areas at a lower latitude.
With Taiwan's dust storm forecast model, forecasters at the EPA can make a prediction 5 days ahead of the dust storm. When a dust storm occurs and it might affect Taiwan in the future, forecaster would, additionally, refer to dust storm forecast models of Japan and the US to determine its strength and the time period that its influence may last.
However, if the dust storm is affected by cloud and rain of a front during the transport process, it is conducive to scouring and depositing the suspended particulates. The EPA refers to weather forecast models of Central Weather Bureau, Japan and the US to analyze whether the dust storm will be affected by the precipitation of a front and determine how the dust storm might affect Taiwan.
Supplementary assessment in determining behaviors of dust storms
Using the data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite, the EPA analyzes graphical data in their full color or aerosol versions, and their optical depths to map the dust storm. However, this method is inherently restricted by the moving course of the satellite and influence of clouds. Dust storm areas tend to be cloudy and the transport paths of dust storms are often obstructed by clouds, making it hard to pinpoint the location of the storms. Therefore, it is very difficult to identify dust storms when they move out of their source region and arrive around the East China Sea. This is a technical challenge that needs to be conquered.
Confirm air quality monitoring results
From past reports and related studies on how dust storms affected our air quality monitoring data, it is evident that dust storms have been riding on the northeast monsoon brought by mainland China's cold high-pressure system going southward. Therefore, the EPA established monitoring stations in Wanli on northeastern coast, Guanyin on the northwestern coast, and Yilan in the East. Even Yang Ming monitoring station in the national park and Matsu monitoring station, established in 1999, can serve as indicating stations to determine the amount of pollution brought by foreign sources. The average concentration of suspended particulates at these stations, normally not directly affected by local pollution sources in Taiwan, is usually below 50 mcg/m3. Once they are affected by foreign pollution sources, the concentration of suspended particulates will raise sharply to more than 100 mcg/m3, starting from northern and coastal areas, and gradually moving to southern and inland areas.
The forecasters at the EPA use the air quality monitoring central system of EPA to read the hourly data of suspended particulate concentration today and the day before, so to determine whether Taiwan's air quality will be affected by the dust storm from East Asia. Using the data gathered from these super monitoring stations, in addition to analyzing concentration of suspended particles (PM10 and PM2.5), we can also analyze the concentration of sulfate, nitrate, organic carbon and inorganic carbon in the fine suspended particulates (PM2.5), along with the amount and diameter of submicron particles to understand the characteristics of the microparticles in the dust storm.
Confirm LIDAR monitoring data
When dust storms affect Taiwan, they increase the concentration of aerosol in the air. Therefore, the EPA installed a light detection and ranging (LIDAR) equipment in National Central University, Zhongli. The equipment can monitor the vertical section of aerosol in the air, which can help us understand the dispersion and strength of the dust storm in a vertical space.
Determine contents after dust storms
The aforementioned process preliminary confirmed that dust particles from East Asia affected Taiwan, but it was, after all, an indirect affirmation. To further confirm that the increased concentration of suspended particulates was due to dust storms in the East Asia, a qualitative research was done by observing the microparticles collected on filter papers. During storm seasons, the PM10 particle samples from most of EPA's monitoring stations were yellowish-brown, which was evidently different from the gray to grayish-black particles collected during non-storm seasons, meaning that the source of PM10 particles was different.
A qualitative research was also done to analyze the incident on March 12, 1995. PM10 particle samples were collected from monitoring stations and analyzed. Comparing to particles in non-storm seasons, the collected particles had significant increase in Al and Ca, and small increase in elements from alkali group and alkali earth group, which is similar to the characteristics of dust particles from East Asia. The result of content analysis further confirmed that the rapid concentration increase of PM10 was indeed due to dust storms in East Asia.
Impacts on people's health and how to prevent them
The negative impacts of East Asia dust storms on Taiwan include deteriorated air quality and lowered visibility. In recent years, the frequency, scale, and strength of East Asia dust storms have been on the rise, leading to an increase in the frequency that Taiwan is affected. Increased particles in the air often trigger allergic rhinitis, causing coughing, asthma, irritation in the eyes, skin allergies or itching. According to statistics from EPA studies, a drastic increase in respiratory syndromes, student absence due to respiratory syndromes, and hospital visits made by people suffered from respiratory syndromes are the three most telling impacts on people's health caused by suspended particulates.
As dust storms bring a tremendous amount of suspended particulates and deteriorates the air quality, it is suggested that people with respiratory or cardiovascular diseases, especially the elderly and children, should avoid going outdoors. If going outdoors is needed, it is strongly suggested that one should wear masks and goggles to filter the polluted air and to avoid direct contact.