Tuesday, 8 August 2017

The AQHI downplays exposures from particulate pollution

How much is a human life worth? If you live in rural British Columbia or in resource-based communities like Kamloops you may be surprised to learn that your life is worth far less than someone from Vancouver or Victoria.

Recent forest fires in the interior of BC, and the massive amounts of wood smoke produced, demonstrate how risk communication tools like the Air Quality Health Index (AQHI) are designed to treat differentially exposures across populations.

The AQHI is a scale used in Canada to weigh the relative contribution of three air pollutants; namely, particulate matter in the 2.5 micron range (PM2.5), ground level ozone, and nitrogen dioxide. It normally ranges between 1-10 or from “low” to “very high” health risk but can reach numbers like 49 as was recorded on August 3, 2017, in Kamloops.

The formula used for calculating the AQHI is straightforward and it involves using a three-hour average for these pollutants in micrograms/m3 for PM2.5, and parts-per-billion (ppb) for ozone and nitrogen dioxide. A weight is assigned to each of these pollutants based on observed adverse health outcomes.

In BC, the air quality objective for PM2.5 (24-hour average) is 25 micrograms/m3. With recent forest fires, numbers have been in the 150-200 range for several consecutive weeks.

The AQHI is mathematically flawed and out of line with these objectives. It downplays the significance of PM2.5 exposures and it generates low AQHI levels when air pollution risks from PM2.5 are actually high.

For example, a community exposed to no nitrogen dioxide, no ozone, and 100 micrograms/m3 of PM2.5 pollution yields an AQHI of 5, or “moderate risk.”  This is actually a staggering amount of pollution yet the risk messaging is tempered and muted. It would take 400 micrograms/m3 of PM2.5 with this scenario to hit a 10 on the AQHI. China issues “red alert” warnings when 24-hour averages exceed 150 micrograms/m3.

The AQHI poorly protects people in rural and resource-based communities from particulate pollution, and it seems designed more for urban environments where ozone and nitrogen dioxide pollution are more common. As a result, this tool exposes us to higher levels of risk.

Michael D. Mehta, Ph.D. (August 8, 2017) 

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