UPDATED: Air Quality Health Index not good assessment of risk

When our smoke levels go up, whether from wildfire smoke in the summer or residential wood burning in the winter, some sources tell people to look at the Air Quality Health Index (AQHI) to see what the health risk might be.

However, we’ve found that the AQHI is not an adequate tool for assessing risk from smoke pollution

In fact, the AQHI can be very misleading in smoke-impacted communities and might lead vulnerable people to think things are okay when they are not. We have recently written to the BC Government to outline our concerns. (Read our full letter)

Fine particulates combined with 2 other pollutants

The AQHI risk level (low, medium, high) is set based on a combination of readings for three pollutants: Ground-level Ozone; Nitrogen Dioxide (NO2) and fine particulates (PM2.5).

Therefore, if the Ozone and NO2 levels stay low (as they often do in non-urban environments) the AQHI health risk stays low even though research tells us there is significant risk with even small increases in PM2.5 exposure.

The study used to develop this system was based on information from 12 major Canadian cities; and it acknowledges that the applicability of the AQHI system and formulas outside of urban centres  may be “legitimately questioned in that there are potential differences in exposure mix, population susceptibility, and time activity patterns.”

This graph shows the diurnal cycle of wood smoke pollution in most smoke-impacted communities. The AQHI often reads “low” even when our smoke levels spike in the evening (grey areas represent 6pm to 1am).

New AQHI+ system being tried

Last winter, there was a new change to the system being tested to try to improve risk warning for fine particulate pollution, but this adjustment continues to be inadequate for smoke-impacted areas.

Under this new “plus” system, the AQHI now jumps to “high risk” if a PM2.5 readings of 60 ug/m3 is reached (and will be locked in for 6 hours). But if the reading is only 59 ug/m3, the risk is often noted as “low”; there is no graduated increase of risk.

So we see situations where we might have readings of 50-59 ug/m3 for a number of hours, yet the health risk will be noted as “low”. Then if we cross the magic line of 60 ug/m3, the risk will jump to “high” and stay there, even if the readings drop significantly, which they often do in the early morning, after a spike at 9 or 10 pm.

We need to delink PM2.5 from the other 2 urban pollutants

We need to have a graduated level of health risk warnings linked to just PM2.5 readings. It should be delinked completely from the other two pollutants which are mostly found in urban areas, to reflect the type of pollution wood smoke impacted communities experience and the very real health risks people are experiencing (the US EPA system does this).

READ OUR LETTER to the BC government regarding our concerns about the AQHI. It contains more details on the issue, with examples, additional concerns and recommendations. 

Posted in Health, Monitoring and tagged , , , , .


  1. A member of the EPA who did not to reveal her name has also commented on the AQHI as being inadequate in not having enough weighting on fie particulates.

  2. Politicians have been hiding behind the AQHI for years while residents choke on levels of wood smoke caused by their neighbour’s wood burning many times higher than at the monitoring unit. A ban on residential wood burning is long overdue regardless of the supposedly clean air as identified at a monitoring station. It is time for our departments of the environment stop trying to take us for fools.

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