BEIJING — Beijing on Aug 21 reported the lowest record for a major air pollution indicator for January-July period since 2013.

The PM2.5 density averaged 64 micrograms per cubic meter in the first seven months of 2017, down 34.7 percent from the same period in 2013, according to Beijing Environmental Protection Bureau.

PM2.5 density measures the concentration of small, breathable particles in the air and is often used as a gauge for smog.

Smog has become a frequent occurrence in North China in recent years, particularly in winter, due to the high concentration of industry, excessive use of coal, climate change and the explosive growth of private vehicles among other reasons.

Beijing has been one of the cities which suffered the most from smog.

The government said PM2.5 levels have been lowered as the city progresses in its 2017 “clean air” targets of replacing coal with clean energy in 4,000 furnaces, removing 300,000 polluting vehicles from roads, and relocating 500 rudimentary manufacturers.

Beijing aims to lower its PM2.5 yearly average from 73 micrograms per cubic meter in 2016 to 60 in 2017. It will be a challenging target as PM2.5 usually increases in winter when the atmosphere is more static and households turn on coal-burning heaters.