AQI, Masks etc 空气质量指数、口罩等

By 2015-02-23News & Info

Pollution is causing major issues for our cycling in China. Its become more of an issue than rain.

Key questions: What AQI is safe for me to ride in & what masks are good for riding etc.

A none political view from an engineers perspective (thanks again JoeM);

A general view on air pollution and filter masks for cycling.

  1. The difference between AQI and PM2.5

Although everybody is talking about AQI, that value is ill-suited to quantify the degree of air pollution. AQI is just a try to express the effect of air pollution to the human body.

  • AQI below 100 means no to minor unhealthy effects to the human body
  • AQI above 150 means more or less harmful to hazardous for the human body.

To express the degree of air pollution, you need to know how much dirt is in the air.

That will be done with the PM2.5 value, which is the density of smaller 2.5µm particles in [µg/m3] in the air.

The relation between PM2.5 and AQI has been “designed” kind of arbitrary by some health organizations and is shown at below figure.



  • AQI=100 à PM2.5=35µg/m3
  • AQI=200 à PM2.5=150µg/m3

Btw. Threshold for the EU is 25 µg/m3, if a city exceeds that value for a number of days in one year, they have to improve their measures to bring it down.

  1. What is the difference between AQI (US Standard) and AQI (Chinese Standard)

For some reasons, China has created its own AQI standard to interpret the Pollution grade. Both standards can be mistaken easily, as they are just called AQI.

The Chinese AQI is mainly used by official sources as TV news, newspapers…

At this Website, we only use the US Standard. Below table shows the difference:


  1. Requirements for Pollution masks

Generally, if you go out cycling at polluted days, I don’t believe any mask will provide you a kind of European conditions.

It just reduces the inhaled pollution to a level you are maybe willing to accept!

For example: If you are riding at 150µg/m3 (AQI 200) but you want breath only 35µg/m3 (AQI100), your mask needs an efficiency of 77% for the whole ride!

Most of us are more than happy if they can ride at 35µg/m3 (AQI100), and still except 67 µg/m3 (AQI 150).

At this place, I just arbitrary set my personal requirements to a mask as below:

I do a masked ride up to 150µg/m3 (AQI 200), and don’t want inhale more than 35µg/m3 (AQI 100). That means the mask needs an efficiency of 77%. Taking in consideration, that my tests are very simplified, I hope to breath not worse than AQI 150 conditions.

With a particle counter it is possible to do a kind of “workbench check” of the filter efficiency (not the whole mask). But because the test is simplified, the only possible result is:

  • The efficiency of the mask is lower than XX %. Hard to say how much lower, but for sure not higher!!!

My Results with totobobo electrostatic filters (96%):

Conditions Filter efficiency tested with particle counter My personal opinion
Fresh out of the box 98% Impressive
Fresh out of the box but soaked in water, tested wet 4%!!!!! Useless
Fresh out of the box but soaked in water, re-dried, tested dry 7%!!!!! Useless
After 30km, at AQI 220, exhaled sometimes into the mask, filters moist. 65% Not to accept
After 50km at AQI 170, tried to exhale only with nose (which is not covered by the mask) to keep the filter dry 82% Maybe ok

My Conclusion:

Forget your mask, when the electrostatic filters are wet!!!!

If you ride outside at polluted days, be clear that the mask has its limitations, an indoor session with air purifier is the healthier option.

I did not test mechanical filters (for example 3M disposal masks or Respro) because in my opinion the breath resistance is too strong for a hard ride.

Thanks JoeM for the above. We are interested to hear other peoples professional perspective such as the EPA & doctors on what they feel are safe levels of pollution to ride in.

Morning_run_Beijing What_cycling_does_to_you_in_Shanghai._Crashes_and_pollution.
Where do i buy masks? At any of the quality bike shops or their taobao sites. Example of the 3m masks as used by many riders here because they hold up when wet and have a valve. Infected lungs after a high AQI day.

AQI is too high, suggestions on indoor trainers available in Shanghai. Coming soon…..

About Joe Muller

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