The city of Seoul says the mass concentration of fine particles in the air recorded its lowest total in 13 years.

It said that Tuesday's measure of fine particles posted 55-micrograms per cubic meter of air. The daily average in the first half was 62-micrograms, down ten micrograms compared to the same period last year. The first-half average was the lowest since the nation began measuring the air quality in 1995.

The number of days with more than 100 micrograms of fine particles per cubic meter of air decreased to 17 days in the first half from 32 days in the same period last year.

Also, the number of days with less than 30 micrograms per cubic meter increased to 23 days from ten days.

Seoul attributed the air quality improvement to the introduction of eco-friendly transit buses and other continued environmental initiatives. Also, it noted that less drivers were on the road due to high oil prices.