The country’s first ever fine dust alert was issued in Seoul on Thursday, as fine and ultrafine dust particles continued to be blown in from China.

The Seoul city government issued an alert as of 4 p.m., with ultrafine dust levels reaching 93 micrograms per cubic meter of air.

Ultrafine dust is defined as particles that measure less than 2.5 micrometers in diameter, or PM 2.5. Along with the ultrafine dust level, that of fine dust ― particles measuring less than 10 micrometers in diameter ― also reached 166 micrograms per cubic meter.

“High concentrations of fine and ultrafine dust generated in China’s (cities of) Shanghai and Qingdao were brought onto the peninsula by the westerly winds,” said Kang Hee-eun, chief of Seoul city’s climate and atmosphere department.

Under the regulations introduced late last month, an alert is issued when a fine dust concentration of over 85 micrograms per cubic meter is maintained for more than two hours. When the figure surpasses 160 micrograms per cubic meter, a warning is issued.

By Choi he-suk (cheesuk@heraldcorp.com)