PA Q+A: PM2.5 Levels

Below is the answer for another PA Q+A . If you have a question you’d like to ask the Prefectural Advisors, or want to see other Q+As, click here.


The PM 2.5 levels seem to have been very consistently high recently. What mechanisms are there to alert schools to ensure the safety of teachers and students? Also, why does there seem to be a discrepancy between Japanese websites and other websites?




Every morning at 7:30AM, forecasted levels of PM2.5 are posted on the Saga Prefectural website and sent on to the municipalities. The numbers are based on measurements taken twice a day at twelve locations throughout the prefecture.

PM2.5 Info Page on Saga Prefectural Website (Japanese)

On this same page you can find the following table of recommended actions for different levels of PM2.5, based on the guidelines set forth by the Environment Agency:


Provisional Measurement Index

Recommended Actions

 Daily Average


Above 70

・Avoid going outside if not urgent or necessary. Avoid strenuous exercise outside for long periods of time.

・Indoors, avoid the unnecessary opening and closing of windows. Try to limit ventilation.

・Those with respiratory or circulatory illnesses (ex. asthma), small children and the elderly may be affected more than others. Individual reactions may vary, so act with caution, paying close attention to changes in health.


Below 70

There is no need to especially limit activities, but those with respiratory or circulatory illnesses (ex. asthma), small children and the elderly may be affected more than others, so pay attention to changes in health.


Saga Prefecture also alerts citizens of high PM 2.5 levels through:

In the case of severe pollution

The Prefecture takes note of when the numbers stay above 35 for several days – but no official notices are sent out at this point. Most people need not worry, but it is worth noting that people with asthma should look after their own health and be careful when it’s above 35.

If and when the forecast go over 70, the following would happen:

  1. The Environmental Division of the Prefecture will notify all of the municipalities.
  2. The municipalities will pass on the information to their BOEs and other organizations that need to be alerted.
  3. The BOEs will alert all of their schools, passing on the guidelines for action.

**So far (since the Prefecture began taking PM2.5 measurements in 2010), this has only happened once, on November 3rd, 2013. It was forecasted to go over 70, but in the end the measurements for that day reached only a high of 40.

A note about AQI and other websites

On some websites you may find that the numbers given for a certain town/city in Saga Prefecture may differ from the numbers given on the Japanese websites. This is because the AQI (Air Quality Index) is calculated according to an algorithm which results in the number being higher than a straightforward measurement of the density of PM2.5 in the air, which is what Saga Prefecture posts. (An AQI of 100 is roughly equivalent to a PM2.5 reading of 50.)

Answered by PAs 2014/3/15.