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A clear day with high dust level

Posted April. 26, 2016 07:24,   

Updated April. 26, 2016 07:30

한국어

South Koreans who had planned a weekend trip last week were hit by the worst air pollution of the year. At first sight, the weather over the last weekend seemed completely different. Saturday’s skies were hazy, let alone the high level of fine dust. On the contrary, the sky seemed cleared up the next day, providing a 6.20-km vision. People were happy that the worst fine dust has gone within a day. Tens of thousands ran at a half-marathon in Seoul, and more than 4,000 joined bike riding and walking festival in Daegu.

However, the figures maintained “very bad” on both days across the nation. An average of 150μg per㎥of 10μm particles is equivalent to “bad,” while an average of 151μg per㎥or more of the particles is “very bad.” On Saturday, 13 out of 16 cities and provinces had “very bad” levels of fine dust, and the number was 8.

High level of ultra fine dust (PM2.5), particles with diameter of 2.5μm and smaller, makes the day hazy. This is because PM2.5 has bigger light-dispersion effect than fine dust. On Saturday, yellow dust also played a role in making the hazy day in addition to fog. On the other hand, Sunday was rarely a clear day despite yellow dust, thanks to low fog and humidity level. The National Institute of Environmental Research announced that there was almost no ultra fine dust during last weekend, which most people finds it hard to understand.

An average of 300μg fine dust level for more than 2 hours will lead to a warning, posing limitations on vehicles on the roads, and working hours. In Gangnam area, one of the busiest districts of Seoul, the fine dust levels exceeded 300μg from 9 p.m. Saturday to 4 a.m. on Sunday, hitting the highest of 479μg. Staying outside for an hour at this level of air pollution is like breathing four hours in a room full of cigarette smoke. Fine dust and tobacco smoke are both first-level carcinogens. However, it would be rare for Seoul City to announce such a warning, because the entire city is bound as a single district for the warning. A warning is likely to be place in Seoul only after a number of respiratory cases have been seen.