Lan Yanfei, 34, moved away from Beijing to escape the heavy smog, vowing never to return for the sake of her children's health.

Lan Yanfei

"I previously worked in Yangzhou, Jiangsu province, but in 2007 I got a job offer in Beijing. At that time, the whole country was excited about the Olympic Games in the capital. I really wanted to witness the event myself and progress in my career there," Lan said.

"Before I moved to Beijing, I only knew about possible sandstorms and dry weather. But fueled by my dreams, I didn't really care about environmental conditions."

Lan's husband, who participated in several projects on environmental pollution, began to educate her on air pollution and its possible effects on health.

"He put on a mask whenever he felt it was necessary. I thought that was a bit weird and when no one else wore a mask on the street, I felt a little bit embarrassed to do so," she said.

"However, I began to take the issue seriously after I had my first baby in 2010. That change forced me to reconsider air pollution and its impact."

Lan's son, Tian Tian, had a fever several times in 2013. When she took him to the hospital, she experienced long lines of anxious parents with their sick children.

"My son got ill easily during smog in Beijing. Even my parents' throats felt itchy and they kept coughing," Lan said. "It was then that I thought it was time to do something about it."

Lan and her husband moved to Yunnan province at the end of 2013. Lan's parents opposed the decision because they thought it would negatively affect her career.

"My parents, friends and colleagues were all shocked when I told them about my decision to move," Lan said. "Of course I made sacrifices. I had to leave behind the employment and networking opportunities in Beijing."

"As a mother, my children's health is my top priority. If you value your job and accommodation, and are willing to compromise your health, you can stay," Lan added. "After all, it is a personal choice."

In early 2016, Lan's family moved to Shenzhen, Guangdong province, for better job opportunities and their children's education. One of her friends has now followed suit.

"One of my friends in Beijing decided to move to Zhongshan, Guangdong province, in 2017 to avoid air pollution," Lan said. "Many people have said I had a vision when I made the choice to leave in 2013. I would say it is because I am a mother."