The Beijing-Tianjin-Hebei cluster saw China's highest levels of pollution last year, according to the report. In the first half of 2013, the 10 cities with the worst air quality - including Beijing, Tangshan, Shijiazhuang, Xingtai and Tianjin - were all within the cluster.

However, the 10 cities with the best air quality, including Haikou, Zhuhai, Zhongshan, Zhoushan and Shenzhen, were all in coastal regions.

"So all of us (to some extent) moved here because it was healthier, but for more general reasons, not air pollution specifically," said Pym, the graphic artist. The lack of industry in the area has resulted in much cleaner air.

Water purity and food safety are equally important factors for Pym. In Dali, water can be drunk from the tap and the food is fresh. Farm-grown vegetables have only a minimal dousing of chemicals, and many Dali residents, both Chinese and expats, grow their own.

A US-born friend of Pym's buys all her milk from a farmer who has just two cows. That way, she can ensure that nothing has been added to the milk, which she uses to make ice cream.

"The environment was a major reason my wife and I made the decision to live here," Pym said.

The smaller, the better

Although she has lived in Beijing for three and a half years, Nina, a Russian woman in her late 20s, has experienced life in one of China's smaller cities. Before she moved to the capital to teach art at an international school, she lived in the coastal city of Dalian in Liaoning province. Her time in the beautiful port left a strong impression on her, not only of the blue sea, cleaner air and a healthier lifestyle, but also closer connections with the expat community.

Nina was first attracted to the city and China as a young girl when her mother visited Dalian and returned to Russia bearing armfuls of gifts, which exposed the girl to a new world centered around Chinese art and crafts. Nina started to dream of traveling to China, finally achieving that goal when she arrived in Dalian in her early 20s.

"There are just a couple of places in Dalian where expats can get together to celebrate or hang out," she said. "The community is kind of fixed - we always knew if anyone new had arrived in town and would have a welcoming party for them. When I was there, there was a small, close circle of friends, not like in Beijing where people come and go quickly and there are several expat hotspots, which means the foreign community is less connected."

Having spent six years in Dalian, Nina has considered leaving Beijing and returning to the port, not only because of the air pollution in the capital. Other factors would also influence her decision. "I like the arts environment here in Beijing and I have experienced a lot of great culture here. However, if I wanted to retire or opt for an easier life, I would definitely return to Dalian," she said.

"There's too much pressure in Beijing - the air quality, the flow of people and the lifestyle," she said. "When I first moved to Beijing, for the first six months I was completely alone without a circle of close friends."

An attractive destination

China is becoming increasingly attractive as a destination for immigrants, with the speed of economic development and the relatively low cost of living cited by many as the main reasons.

In some places, it's still possible to set up your own business without too much stress, according to Pym. His wife has opened a caf in Dali, something she couldn't imagine doing in Shanghai, given that rents and other living costs are so high there.

If anything were to make them consider leaving China, it would be their son's education, rather than the level of pollution, according to Pym. Their son will be fine until he reaches high-school age, but unless a school with high educational standards opens in Dali in the next few years, the family will probably have to leave.

But should circumstances force them to move, Pym has no idea where they would go next. As an illustrator for several publishing houses and magazines, he could return to the UK, but equally he could move elsewhere.

"But like I said, it's years till we have to make a decision, and hopefully we will be able to stay," he said.