How is the AQIH calculated?

The Air Quality Index for Health (AQIH) has 10 points ranging from 1 to 10. These points are divided into four coloured bands – good (readings of 1-3), fair (readings of 4-6), poor (7-9) and very poor (10). The higher the number the worse the quality of the air.  For example, a AQIH reading of 10 means that the air quality is very poor and a reading of 1, 2 or 3 means that the air quality is good (see table below).

The AQIH is based on measurements of five air pollutants all of which can harm health. The five pollutants are: 

o    Ozone gas

o    Nitrogen dioxide gas

o    Sulphur dioxide gas

o    PM2.5 particles and

o    PM10 particles 

We use automatic air quality monitors to measure how much pollutant there is (we work this out per each cubic metre – m3) per hour.

The pollutants measured at each station vary. All five pollutants are not measured at each site. Most monitoring stations measure particulate matter as these present the greatest health risk. Nitrogen dioxide is monitored mainly in urban areas with significant exposure to vehicle emissions.

For each monitoring station, we work out the index number for each pollutant separately. The overall  AQIH is the highest available pollutant index. For example, if the ozone index figure is greater than sulphur dioxide, we give the higher ozone index as the overall AQIH. The table below shows the ranges of concentration (amounts) for each pollutant. Examples of how to calculate the AQIH are given below the table.  

AQIH table of pollutants

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