Beijing slashed levels of a major airborne pollutant by over a third in five years, reaching a target set in 2013, and also recorded 226 "blue sky" days in 2017, the city's environmental authority said on Wednesday.?

In 2017, the annual average concentration of PM2.5 — hazardous fine particles — was lowered to 58 micrograms per cubic meter, reducing the 2013 level of 90 micrograms by 35.6 percent, said Liu Baoxian, deputy director of the Beijing Municipal Environmental Monitoring Center.?

"It means Beijing reached the target set by the State Council of lowering it to 60 by the end of 2017," he said.?

Residents also have seen blue skies frequently despite the arrival of cold weather, with only five days with severe air pollution recorded from October through December, the bureau said. It's a big drop from previous winters, when heavy haze led to alerts, including top-level red alerts.?

"In 2017, Beijing had 226 days of good air quality, increasing from 176 in 2013," Liu said. A day with an average Air Quality Index of 100 or below is considered to have good air quality.

The year also saw large reductions in other pollutants, especially sulfur dioxide.?

"The average annual concentration of sulfur dioxide saw a historical low of only 8 micrograms per cubic meter," Liu said, adding that the national standard is 60.?

"The dramatic improvement in air quality mainly resulted from effective and extra-strict controls on emissions and advantageous weather to disperse pollutants," said Li Xiang, director of air quality management at the capital's Environmental Protection Bureau.

Restrictions covered many sources, such as factories, vehicles and burning of coal, she said, adding that over 11,000 polluting companies were closed or moved.?

Wang Shuxiao, professor of environmental studies at Tsinghua University, said preliminary results showed the restrictions worked better than favorable weather like winds on air quality.

By 2020, PM2.5 is forecast to be lowered to 56 micrograms, Li said, adding that the air quality will see "essential improvement" by 2035.

The national standard for PM2.5 is 35 micrograms per cubic meter.