The number of days showing poor air quality in capital Seoul have jumped threefold since regulations on fine dust levels were tightened to match the standards of other advanced nations one month ago.

According to the National Institute of Environmental Research on Saturday, ultrafine dust particles measuring under two-point-five micrometers in diameter indicated a level of "bad" on seven days between March 27th and April 26th.

"Bad" implies fine dust concentration ranging between 36 and 75 micrograms per cubic meter (㎍/㎥).

Applying the previous looser standard of 51 to 100 micrograms per cubic meter, the number of "bad" days drops to just two.

An enforcement ordinance for a revised Framework Act on Environmental Policy was approved by the Cabinet on March 20th and took effect on the 27th. 

The revised law calls for tightening standards on fine dust levels.

Under the changes, the daily limit on PM2.5, which is fine dust with diameters smaller than two-point-five micrometers, has been lowered from 50 to 35 micrograms per cubic meter. For the annual average, the standard has been tightened from 25 to 15 micrograms per cubic meter.