Heavy smog has returned to the skies of Beijing after a two-month break, with authorities predicting the pollution will linger due to unfavorable conditions.

The density of PM2.5, or particulate matter with a diameter of less than 2.5 micrometers that can harm the heart and lungs, reached 400 micrograms per cubic meter early on Monday, well above national and international standards, the Beijing Municipal Environmental Monitoring Center said.

The center said due to rising temperatures, lack of wind and other unfavorable conditions, the pollution is unlikely to disperse in the next few days.