New data finds that South Korea and China both saw a clear decline in ultra fine dust levels last year.

The environment ministries of the two countries unveiled the data on Wednesday as they jointly announced plans to address fine dust and ways to cooperate on lowering dust levels. 

It marked the first time the two countries have disclosed joint government data on air quality. 

South Korea’s ultra fine dust levels in 2020 reached 19 micrograms per cubic meter, or down nearly 27 percent compared to 2015 when the government began to compile related data. 

In particular, the number of “bad” days, or periods when the levels are 36 micrograms per cubic meter or higher, dropped by roughly 56 percent to 27 days compared to 2015. 

The number of “good” days last year amounted to 154, or the largest figure to be recorded since observation for fine dust began. “Good” days refer to periods when levels of particles smaller than two-point-five micrometers in diameter drop below 15 micrograms per cubic meter.

China’s ultra fine dust levels in 337 cities amounted to 33 micrograms per cubic meter on average, down more than 28 percent from 2015.