Beijing issued this year’s first air pollution warning on Wednesday night as pollution readings reached “beyond index” levels.

The Air Quality Index (AQI) measured at all six Beijing downtown districts and every southern suburban region on Thursday morning far surpassed 300, the threshold for the worst level in a six-scale table, according to data from Beijing Environmental Protection Monitoring Centre.

Most of these regions have readings measured at the 400 to 500 range. The environmental protection authority does not differentiate between pollution levels after it they pass 300 – all of which fall under the “severe pollution” range.

The AQI indicates the amount of PM2.5 particles in the air which measure less than 2.5 micrometres in diameter. The tiny inhalable particles are believed to pose more risks to human health than bigger particles like PM10 because they can travel deeper into the lung and cause more severe health issues.

The International Agency for Research on Cancer, the specialised cancer agency of the World Health Organisation, last year for the first time linked outdoor air pollution with cancer deaths. It said PM2.5 contributed to 223,000 deaths from lung cancer worldwide.

The US Embassy in Beijing, which also measures AQI in the form of PM2.5 concentration, put the number at the upper 400 range or “hazardous level” on Thursday morning, according to a Twitter account that publicises the readings every hour. At 4am it reached 671.

The air pollution level began to surge at around 9pm on Wednesday night, according to the Beijing Municipal Environmental Protection Bureau, prompting the authority to issue a “blue” heavy pollution warning.

The pollution is expected to slowly disperse as early as Friday midday, the authority predicted.

Air pollution has been on the rise in recent years in cities across China as pollution monitors have observed staggering amounts of serious air pollution. Experts say the primary sources of pollutants are emissions from motor vehicles, coal burning, and scattered construction sites.

The eastern coastal city and economic hub of Shanghai experienced pollution for more than a third of last year, the city’s environmental protection bureau said on Wednesday. Just 52 days were considered “good” in terms of air quality.

via Beijing hit by first bout of ‘off the charts’ air pollution of 2014 | South China Morning Post.