The nation recorded the lowest level of ultra fine dust since 2012 last year thanks to fewer old diesel vehicles, according to a recent study.

Conducted by the National Institute of Environmental Research, the study showed that ultra fine dust in South Korea peaked in 2014, recording over 37 micrograms per cubic meter, then gradually declined to around 23 micrograms in 2018 and slightly over 21 micrograms in 2020.

The concentration of particles less than 100 nanometer also dropped by nearly 27 percent between 2018 and 2020. These particles are known to be emitted mostly from diesel vehicles.

The institute analyzed that the lower level of ultra fine dust and smaller dust particles can be attributed mainly to the reduced number of old diesel autos. 

The number of diesel cars dropped from roughly 930-thousand in 2018 to around 546-thousand last year.