[Definition of PM]

"PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope (EPA)."

[Classification of Particulate Matter]

Classification of PM 10 & PM 2.5

PM 10

Inhalable particles
Diameters around 10 micrometer

PM 2.5

Fine inhalable particles
Diameters around 2.5 micrometer

[Causes of Particulate Matter]

Particulate matter comes from two different kinds of sources, primary and secondary. The primary sources could be wood stoves or forest fires that cause particulate pollution on their own. The secondary sources are factories, cars, and construction sites that let off gases that can form the particles.

Primary Sources

The primary source of PM is obtained from both human and natural activities. Most of the PM sources are generated from various human (anthropogenic) activities. The activities include agricultural activities, combustion of wood and fossil fuels, dust, and forest fires blown by the wind.

Secondary Sources

Fine dust is generated through chemical reactions in which sulfur oxides emitted during the combustion of fossil fuels such as coal and petroleum combine with water vapor and ammonia in the atmosphere, or nitrogen oxides from automobile exhaust combine with water vapor, ozone, and ammonia in the atmosphere.

Effects of Atmosphere on PM 10

[Climate change]

Climate change causes temperature rise and humidity change. These changes are related to changes in the concentration of PM because they affect the spread and movement of air pollutants. In particular, considering that the increase in ozone concentration is due to photochemical smog in the atmosphere and that the causative substances are nitrogen oxides (NOx) and volatile organic compounds (VOCs), what can be seen through the mechanism of changing gaseous substances into particulate substances is that climate change can affect fine dust concentrations in the atmosphere (Fuzi et al., 2015). In a study by Tai, Mickey, & Jacob (2010), weather variables (temperature, humidity, precipitation, circulation) in the atmosphere can be explained up to 50% of the ultrafine dust concentration variation, and stagnant atmosphere has an average ultrafine dust concentration of 2.5㎍/㎥ higher than circulating atmosphere.

[Temperature Inversion]

The temperature in the atmosphere generally decreases by about 0.6℃ when the altitude rises by 100m. Conversely, however, there is a phenomenon called "Temperature Inversion" in which, the higher the altitude, the higher the temperature rises. Temperature inversion often occurs in seasons with large daily temperature differences or in mountainous basins. Usually, the hotter the air, the lower the density, so the hot air moves up and the cold air moves down. However, when the temperature inversion occurs, heavy air is located on the lower side and light air is located on the higher side, so the air does not move up and down due to the weight difference. Then, air pollutants such as PM, which are mainly generated on the ground, remain in the ground layer and continue to accumulate, increasing their concentration.

[Seasons]

Particulate matter also varies greatly from season to season. First of all, high concentrations of PM accompanied by yellow dust are likely to occur in spring due to the influence of cyclones and dry surfaces. On the other hand, the concentration of PM is likely to decrease in summer when there is a lot of rain. This is because when it rains, air pollutants such as PM are washed away by raindrops and removed, thereby cleaning the atmosphere. In autumn, PM is relatively low because the flow of the barometer is faster and the local atmosphere is well-circulated compared to other seasons. In winter, when fuel usage increases, the concentration of PM may increase again. In the case of Seoul, the concentration of PM10 by season from 2012 to 2014 was 30~60㎍/㎥, which was high in winter and spring, and relatively low in summer and autumn.

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