Health Impacts of Fine Particulate Matter

by Ron Hartling

Fine Particulate Matter (PM2.5) consists of a mix of tiny solid and liquid airborne particles measuring less than 2.5 micrometers (μm) in diameter, too small to be seen individually even through most microscopes but appearing as a haze when present in high concentrations. Unlike larger PM10 particules, our bodies cannot expel them through natural mechanism like coughing and sneezing. The larger PM2.5 particles get trapped deep in our lungs whereas the smallest can pass through lung tissue into our bloodstream. While PM2.5 particles can include pollen, liquid or solid aerosols or biological matter such as mould spores, bacteria, and pollen, most of what afflicts us today consists of industrial or wildfire combustion products.

The science behind PM2.5 health risks

The above pair of charts constitutes the “smoking gun” in terms of why it is very much in our long-term best interests to take some of the simple precautions summarized in the parallel “self-protection” page to significantly reduce our very real risks of premature death and debilitating medical conditions in our later years.  In a nutshell, breathing airborne particulate matter kills, lowering one’s life expectancy and increasing susceptibility to the wide range of chronic disorders illustrated in the above mortality chart. The smaller those particles, the greater the damage from both short-term bursts and long-term exposure.  As with lead poisoning, there is no safe level.

While PM2.5 particles are only one of six airborne pollutants whose levels are used in a complex formula to compute the Ontario government’s Air Quality Index, they are the deadliest component of both wildfire smoke and heavy-industry emissions. They are also arguably the only one of those airborne pollutants for which ordinary people can realistically and affordably manage their personal and household exposures from the perspectives of both life expectancy and quality-of-life in one’s later years.

The vertical axis in global mortality chart above measures deaths associated with each of the specific chronic conditions associated with breathing PM2.5 pollutants where the dashed black line provides an overall total. Note especially the critical 5.8 µg/m3 average annual exposure threshold for rapidly-rising mortality.  Since neither we nor any level of Canadian government have any lever to reduce the flow of industrial pollution flowing across the border, our only option is to better manage our personal exposure.

Note that the short- and long-term health consequences for varying levels of PM2.5 exposure as listed in the table at the top right of our Home page differ quite radically. The impacts of short term exposure for all but the most susceptible people tend to be comparatively mild up until the higher concentration levels. By contrast, the global mortality chart shows a very abrupt escalation of serious and potentially fatal long-term health impacts soon after average annual PM2.5 concentrations exceed Level 0. Surprisingly, while the probabilities of very severe consequences such as Ischemic Heart Disease and Stroke continue to rise with increasing PM2.5 concentrations, the slope is less than linear.

According to this global chart of lost life expectancy by cause, choosing to manage one’s PM2.5 exposure is even more important than cessation of smoking.  For many, the loss of quality of life in their final years due to the pain and limitation of living with the above disorders would be even more of a concern than reductions to their overall life expectancy.  Most other factors that can reduce one’s quality of life in later years are at least partially attributable to lifestyle choices rather than being imposed by external actors who profit from their freedom to pollute the air that the rest of us must breathe.

Why the WHO recommendations are more credible

The WHO recommendations are far more credible than the US PM2.5 limit of 12 µg/m3 (echoed by Canada) because they are based on hard evidence from a multitde of recent studies which have almost uniformly found that even relatively low PM2.5 concentrations cause severe disease and large numbers of premature deaths.  For example, the WHO estimates that ambient (outdoor) air pollution caused 4.2 million premature deaths worldwide in 2019 alone.

In response to that new information, the WHO in 2021 halved its previously-recommended maximum average annual PM2.5 exposure from 10 µg/m3 to 5 µg/m3, slightly below the 5.8 µg/m3 damage threshold illustrated in the global mortality graph above.

The politics behind the US and Canadian limits

By contrast, the US average annual limit for PM2.5 exposure which Canada dutifully follows is 12 µg/m3, well into the danger zone.  That limit was last lowered from 15 to 12 µg/m3 in 2012, overcoming years of industry legal and other challenges. In 2020, after an extensive review which found plenty of evidence for that limit being insufficient to protect American’s health, the EPA ultimately chose to leave the existing ceiling unchanged.  To its credit, early in 2023 under the Biden Administration, the EPA launched a consultative process early in 2023 to further reduce its limit to a level between 9 and 10 µg/m3, still well within the zone of rapidly increasing disease and premature mortality. One can only speculate why they would have chosen a number which, if approved, would facilitate proven death and suffering, but the most likely explanation is that it was deemed to be the best that they could hope to get away with in the current political climate inf the face of industry lobbying. Frankly, given the extent of lobbyist control over Congress, even the watered-down EPA proposal most likely stands the proverbial snowball’s chance of approval in face of knee-jerk opposition to more “bureaucratic red tape” burdening industry.

When lives and health are at risk (my own very much included), I place far more credence in WHO’s evidence-based process than anything that North America’s ever-more politically-driven regulatory systems remain capable of producing.