The level of ultrafine dust was bad or worse only on 17 days last year, the lowest on record, thanks to lower dust levels in China, the environment ministry said Monday.

South Korea categorizes concentrations of ultrafine dust -- particles smaller than 2.5 micrometers in diameter, also known as PM 2.5 -- into four levels. PM 2.5 between 36 and 75 micrograms per cubic meter is categorized as "bad," while density higher than 76 micrograms per cubic meter is "very bad."

During 2022, the ultrafine dust level reached bad or worse on 17 days, six days fewer than in 2021 and the fewest since the ministry began ultrafine dust observation nationwide in 2015.

The number of days the ultrafine dust level went up to bad or higher in 2015 was 62.

In 2022, in particular, the dust level did not once go higher than bad.

Of last year, the ultrafine dust level remained "good" on 180 days and "normal" on 168 days.

The average ultrafine dust density last year stood at 18 micrograms per cubic meter, the all-time low on record and the same as a year before. In 2015, the figure was 26 micrograms per cubic meter.

The environment ministry attributed the fall last year to lower ultrafine dust levels in China, and increased precipitation in Seoul and central areas in South Korea. (Yonhap)