According to Tuesday's news report, the Seoul Metropolitan Office of Education has "banned outdoor classes and activities at all elementary and secondary schools in the capital all day." We also get warning messages on our phones, and there is a free app that lets users know of the air quality.
Fine dust is one of South Korea’s greatest enemies. Fine dust particles are about less than ten micrometers in diameter (i.e., very very tiny!) and due to this size, they can enter our lungs as we inhale. It has been said that these fine dust particles cause respiratory problems and are carcinogens. In addition, they are especially harmful for chronically ill patients, children and the elderly, whose immune systems are not as strong. The fine dust can come from factory smoke, or internal-combustion engines. Sometimes it mixes with the so-called “yellow dust” that is blown from the deserts of Mongolia. When the air is bad, I make sure to limit being outside, close my windows and wear a fine-dust-specific mask when I step out, and I take a long shower once I get home. I did some personal research on my own and found a study that says B vitamins provide protection against air pollution, so I make sure my immune system is well fed and well kept.
Here are readings if you want further information:
http://www.koreaherald.com/view.php?ud=20190305000654
https://www.bbc.com/news/science-environment-39231896