While winter temperatures usually drop with the arrival of northeastern winds that sweep across western Taiwan, people may have also noticed worsened air quality, or even experienced mild symptoms of eye irritation, sneezing or coughing in the past months.
The Environmental Protection Administration’s (EPA) Department of Environmental Monitoring and Information Management Director Chu Yu-chi (朱雨其) said the department’s data showed that there have been seven haze and dust storms since December last year.
According to data from the EPA’s air quality monitoring network, the concentration levels of particles under 2.5 micrometers in diameter (PM2.5) detected at nearly all of the nation’s 76 monitoring stations rose drastically as air pollutants were brought in from China by strong winds.
On Dec. 10 last year, PM2.5 levels detected at 72 stations surpassed 80 micrograms per cubic meter (μg/m3).
The nation’s daily average and annual average PM2.5 concentration standards are set at 35μg/m3 and 15μg/m3 respectively.
When obscured by cross-border haze, the pollution standards index (PSI) readings — which are based on the highest concentration value of five major air pollutants PM10 (particulate matter 10 micrometers or less in diameter), sulfur dioxide, nitrogen dioxide, carbon monoxide and ground-level ozone — at most stations reached unhealthy levels and a few in central and southern Taiwan reached hazardous levels.
The EPA’s data also showed that the nation’s average PM10 level of 64μg/m3 and average maximum readings of 256μg/m3 in December last year were higher than those of the same month in the previous two years — 53μg/m3 and 163μg/m3 in 2012, and 50μg/m3 and 150μg/m3 in 2011.
Currently, the standards for daily average and annual average PM10 concentration levels in Taiwan are set at 125μg/m3 and 65μg/m3 respectively.
“The two main factors considered when determining whether the air pollutants are from cross-border pollution are recent weather phenomena and monitoring data on the air pollutant levels in China’s major cities,” Chu said, adding that “generally speaking, these situations [of worsened air quality caused by air pollutants from China] occur every winter.”
However, he said the department has noticed that the frequency and concentration of elevated pollution levels detected this year have been slightly higher than previous years.
Air pollutant levels detected at stations located in Yunlin, Chiayi and Greater Tainan often topped the list of stations, the EPA department’s Deputy Director Chang Shuenn-chin (張順欽) said, adding that this was because fugitive dust — particles suspended in the air by wind action and human activities — at riverbanks during the low-flow season of winter are swept up by the strong northeastern winds.
“The fugitive dust at Jhuoshuei River (濁水溪) during the northeastern monsoon season is not a new phenomenon,” he said.
He added that the frequency and scale of Choshui River fugitive dust have increased in recent years, clearly worsening air quality in central and southern areas.
Analyzing the readings from various agencies, the department discovered that when strong earthquakes above magnitude 5, such as the magnitude 7.3 921 Earthquake in 1999, shake loose soil on upstream slope areas, which is then washed downstream by torrential rains during the summer, land collapse and mud slides are likely, which creates dust on riverbanks, Chang said.