Expatriates living in Beijing were pleased when the levels of air pollution in the city were improved ahead of the Olympics in 2008, but the situation is getting worse again.
It is becoming so bad that some foreigners who have lived in the capital city are thinking of moving to another part of China or a new country all together, reports the South China Morning Post.
The World Health Organization suggests that levels of PM2.5 respirable particles be kept below 25 micrograms per cubic metre.
In Beijing, however, these levels regularly get as high as 100 or 200 with even readings of 900 micrograms per cubic metre recorded last weekend.
Joshua Dyer, a translator from the US, moved to China in 2008 when the situation was very different. He told the news provider: "It was surprisingly good. Many blue skies [back then]. But what happened over the weekend was really shocking.
"The air pollution is one reason I know I can't stay much longer here. I feel the bad air affects me psychologically as well. I feel sluggish on heavily polluted days."
Last year the American Chamber of Commerce in China carried out a study into the issue and how it affects businesses operating in the city.
It found that 36 per cent of the 244 companies surveyed had experienced problems recruiting senior executives, as many were put off by the quality of the air in Beijing.
This is up from 19 per cent in 2010, showing that the economy may start to suffer as a result of the pollution in China's capital city.
A number of other cities in China, including Shanghai, experience pollution problems, but Beijing tends to be the worst.
As a result, many of those who live in cities can be seen walking the streets wearing masks over their mouths in an attempt to limit the amount of pollution they breathe in.
Unless a similar effort to that which was made in the run up to the 2008 Olympics is undertaken again then China may find that it loses some of its expats to other countries where the air pollution in the cities is not as bad.