It’s yellow sand season in Japan right now. You’re easily forgiven if you have no idea what I’m talking about. I didn’t either until just a few years ago. But in a world where awareness of the potential for ecological catastrophe is increasing every day, it’s worth considering the implications of this unusual phenomenon.
“Yellow sand” in this context refers to the fine yellow colored dust residing on the surface of the great deserts of Kazakhstan, Mongolia and central and western China, the best known of which is probably the Gobi. Often during the year, especially in the spring months (March, April and May), dust storms and desert winds stir up the sand, which rises upward where it is carried along eastward by the prevailing winds. How far eastward? As you might guess, it tends to blow all the way across the Sea of Japan and into Japan itself.
But not infrequently, it manages to hitch a ride on the higher altitude winds and land as far away as the US West Coast in a trans-Pacific journey of around 13 days. The most extreme case in recent memory seems to have occurred in April of 2001, when a persistent haze was observed in Southern California that limited visibility to a little as 10 miles, even under the usually clear skies of Death Valley.
The yellow sand phenomenon is not new. It was reported in China as early as 1150 BC, and in Korea as early as 174 AD. Generally, Korea does seem to get a heavier dusting of the particles than Japan. But since the advent of the 21st century, yellow sand episodes have become longer and more frequent, as industrialization and water diversion programs have increased the square area that these deserts occupy. One analysis from Korea reports that the average number of days in which yellow sand episodes occurred increased from 2 in the 1960’s to 11 in the 2000’s.
The dust particles that make up yellow sand are so fine that you often can’t see them in the air, or sense them when you breathe. Their most visible manifestation is as a thin yellow layer coating cars that are parked overnight.
But that doesn’t mean the yellow sand isn’t dangerous. These days, thanks to industrial pollution and aggressive use of agricultural chemicals, yellow sand contains a mixture of toxins that include heavy metals such as mercury and cadmium, pesticides and herbicides, asbestos, and even biotoxins such as viruses and bacteria.
Yellow sand particles are also dangerous because they can be very small. I’ve found that you can’t simply rely on the air quality index (AQI) reported on your cell phone’s weather app. You have to look more closely. The AQI is constructed as a weighted composite of several pollutants, including sulfur dioxide, carbon monoxide, ozone, and particulate matter.
Concentrations of particulate matter are typically measured in terms of large (PM10 — less than 10 micro-meters in diameter) and small (PM2.5 — less than 2.5 micro-meters). Yellow sand tends to consist of a mixture of PM2.5 and PM10 particles, so it helps to look at both.
PM2.5 particles, which qualify as ultrafine particulate matter, are the most dangerous. Ultrafine particles can actually be absorbed through the skin, or if they are inhaled, penetrate unresisted into the bloodstream and lymph systems, piling up in organs and even possibly the brain.
If you click on your weather app’s air quality box (at least it works this way on my iPhone), it will show you the current AQI details, in terms of the concentration of various components. The breakpoints between moderate (but still generally acceptable) and unhealthy levels of pollution are around 35 for PM2.5 and 150 for PM10 (measured in micro-grams / cubic meter). This makes a certain amount of sense because the PM10 particles, being larger, will tend to weigh more.
At the time of this writing, April 22, 2026 at 11:45am Japan time, the concentrations for Kyoto read 13 for PM10 and 7 for PM2.5, well below the danger zone. However, I noticed that about an hour ago, the figures were both 7. In other words, PM10 is increasing, but PM2.5 appears relatively stable for the time being.
If you want more information, the Japanese Meteorological Agency (www.data.jma.go.jp) has some maps and pages available in English. Or you can try accessing the many Japanese websites that provide lots of maps and numbers. You don’t have to know much Japanese to do this. Simply type “こうさじょうほう” or even just its Roman alphabet equivalent, “kousa jouhou” into the Japanese version of Google, and previews of several such sites will appear.
If you are visiting Japan or Korea during the yellow sand season, you are well-advised to take the warnings seriously. Wear long pants and long-sleeved shirts, high-quality (N95, KN95 or similar) masks, glasses or goggles, and of course a hat. Keep your windows closed and run your air purifier. Avoid outdoor exertion. And when you do come back inside, be sure to wash your exposed skin areas (hands, arms, face, etc.) thoroughly.
Or maybe consider a different destination for your next vacation trip 😊.