SHANGHAI • Air quality in China's smog-hit northern regions, which include the capital Beijing, worsened last month despite overall improvements over the year.
The latest update from the environment ministry came as air quality worsened overnight in Beijing.
The Chinese capital, already hit by four episodes of smog since last month, is forecast to be shrouded in smog from last night until Friday.
The Ministry of Environmental Protection said in a notice late on Monday that concentrations of small pollutant particles in the air known as PM2.5, a key smog indicator, fell 12.5 per cent to an average of 42 micrograms per cubic metre from January to last month.
But last month, smog concentrations in the Beijing-Tianjin-Hebei region, a front line in China's war on pollution, were worse than in the same period last year, it said.
It also said six of the worst-performing cities over the first 10 months were in the industrial province of Hebei, which surrounds Beijing. Xi'an also appeared on the list of the 10 smoggiest cities.
Smog normally worsens in winter as China's largely coal-fired urban heating systems are activated in the northern regions, but the ministry has warned that it could be more challenging this year due to unfavourable weather conditions.
Experts have warned residents in northern China to brace themselves for more smoggy weather in the coming weeks as the La Nina weather conditions coincide with the start of the winter heating season in the middle of this month.
La Nina is a periodic cooling of the surface of the equatorial Pacific Ocean, which causes abnormal weather patterns. This year's winter is expected to be colder, wetter and therefore snowier than normal.
Apart from Beijing, neighbouring cities such as Tianjin and those in Hebei province have issued emergency response alerts.
During several recent smog build-ups, the ministry dispatched inspection teams to establish whether emergency smog alert systems in Beijing and Hebei were being implemented correctly.
It found that local governments were not cracking down hard enough on firms that broke rules.
The alert systems let the authorities limit traffic, suspend construction activities and force firms to cut production during heavy smog.
Beijing has closed down dozens of industrial enterprises, shut down coal-fired power plants and replaced coal heating with natural gas in a bid to tackle smog. Cities in Hebei have also been under pressure to cut coal consumption and impose tougher punishments on firms that exceed emission limits.
Environment group Greenpeace said in a research report published on Monday that Beijing's efforts to cut coal burning have led to a 90.4 per cent fall in arsenic concentration levels since 2013, meaning the city now meets national standards.
Beijing set up an air pollution clean-up fund of 760 billion yuan (S$157 billion) in 2014, with its then-mayor Wang Anshun promising that the city's smog problem will be solved by next year.