Since last week Shanghai has been experiencing heavy pollution. Local pollutants and those from the north inland regions of the country, as well as weak winds have been blamed for the situation.

Last week, Shanghai's environment watchdog issued a "heavy pollution" warning when the Air Quality Index (AQI) passed 200.

According to Shanghai Evening Post, Shanghai has a six-tier air quality system. Heavy pollution alerts are issued when the AQI remains above 200 for 12 consecutive hours, the density for PM2.5 particles reaches 150 micrograms per cubic meter and there is no sign of improvement in the next 24 hours.

A severe pollution alert is issued when the AQI remains above 300 for six consecutive hours, the PM2.5 hits 250 micrograms per cubic meter and there is no sign of easing in 24 hours.

When the AQI exceeds 300, the air pollution can put even healthy people at risk of illness.

What do Shanghai expats think about the city's pollution? Are they worried about the possible affect it might have on them? What precautions do they take against Shanghai's air pollution?

Julian Bian, from the UK, graduate student

"I have been really worried about how bad the pollution had been over the last couple of weeks.

I know that the authorities advise us to stay indoors on particularly polluted days but I don't really have that option - I need to go out to get to school. Even if the smog is really bad, I still need to commute to my classes every day. The past few days have been really horrible and I can feel it in my lungs and my nose when I breathe in.

I have been considering buying a face mask to protect myself at least a little bit from the harmful particles. I read reports saying that the pollution these few past days was even worse than in Beijing, which must mean that it was really bad.

Shanghai pollution is a constant concern for me living here and also one of the possible factors in deciding how long I am going to stay in China."

Heather Mason, from the US, designer

"I just got back from Europe and immediately it hit me how polluted the air in Shanghai is. After reading the news about how bad the pollution was last week, I decided to buy a mask.

The air in Shanghai is especially bad for me as I suffer from asthma and sometimes the smog makes it difficult to breathe when I'm walking outside. I used to live in Beijing, but the pollution there, with my asthma, was just unbearable so I decided to move to Shanghai hoping that the air was just a little bit better here. But last week proved that the air in Shanghai is just as bad as it is in Beijing.

I do take some precautions against the horrendous smog. I have an app on my phone telling me the levels of pollution and I check that every morning. If it is especially bad, I try to avoid going outside and I work from home. I have face masks for when I go outside and I have bought air filters for my house."

Stephen Kaye, from Canada, teacher

"Yes, I am a little bit worried about how bad the pollution is in Shanghai. But I am also a smoker so I am probably doing more harm to my lungs myself than the pollution is doing it to me.

I have lived in China for few years now and I've kind of got used to the smoggy skies most of the time and I often forget about how bad the pollution is. The only time I am reminded is when I go back home and see the difference between the air quality here and back there.

But pollution is not only China's problem. It is a problem for any big developing city anywhere in the world. I recently came back from Bangkok and it is even worse there.