Extreme Yellow Dust in Seoul, 2015-Feb-22

A couple weeks ago I had posted about the emergency alert message we in the Seoul area received, warning us of a particularly bad bout of yellow dust (황사). And boy was it bad. The period between February 22-23, 2015 was the worst for yellow dust in five years. I was out and about during that time, and if I'm being honest, it didn't seem all that bad to me. Just another of the occasional hazy yellowdust days. But the numbers sure tell a different story.

Here are just a few interesting images I had saved, that show a little bit, with facts and figures, of just how bad it really was. Take a look. All of these are screenshots taken either Feb. 22 or Feb 23, 2015.

AQICN's air quality map of Seoul region,
as posted by u/torbjorn_bradda

Korea Environment Corporation's "AirKorea" mobile site

My Google Now air quality card, on Feb. 21, 2015

My Google Now air quality card, on Feb 22, 2015

Yellowdust Twitter bot's tweet

KMA's Asian Dust historical tracking chart

A nice, simple introduction to the yellow dust phenomenon can be found here at the KMA's website, including this interesting account of yellow dust in ancient Korea:
The first record of the dust phenomenon in Korea is found in the reign of Silla Dynasty's King Ahdalla (174 A.D.). It was called "Woo-To". At that time, the people believed that the God in the heaven became so angry that they lashed down dirt instead of rain or snow. This is why, whenever the King or his subjects saw a dust phenomenon, they would be frightened.
In the reign of Baekje Dynasty's King Kungusu in 379 A.D., there was the following record in April: "Dust fell all day long." There was a record that the sky of the Baekje's capital was darkened like night by dustfall in march in the reign of King Mu (606 A.D.).
Although these dust phenomena mainly occur during the springtime, there were some records of them occurred in winter as well. During the reign of Goguryeo Dynasty's King Bojang in 644 A.D., it was recorded that there was a red snow that fell from the sky in October. We can guess that Asian Dust was mixed with snow at that time.
The definition of Asian Dust event was introduced in the 「Goryeosa」 as follow: "There was dirt on clothes without getting wet by rain." It was called "Mae () or To-Woo".
In the Joseon Dynasty(1392~1910 A.D.), there was the following record in March 22, 1549: "Dust fell in Seoul. At Jeonju and Namwon in the Jeolla province, located in the southwestern part of Korea, there was a fog that looked like smoke creeping into every corner in all directions. The tiles on the house roofs, grass on the fields and leaves on the trees were entirely covered by yellow-brown and white dusts. When the dust was swept, it wiped away like dirt, and when it was shaken, it dispersed, too. This weather condition lasted until March 25, 1549." This record clearly depicts the characteristics of a dust phenomenon in Korea.
And if you're still here, the Wikipedia article on Asian Dust, and a Google image search of what it looks like.