Where do Eastern Ontario’s bouts of high PM2.5 levels originate?

by Ron Hartling

As discussed in the Evidence page, time-of-day and day-of-week PM2.5 statistics overwhelmingly point to distant 24/7 industrial sources as being the primary culprits. Also on that page, long-term correlations with wind direction equally overwhelmingly point to US rather than Canadian sources.  With the occasional seasonal exception of wildfire smoke, northerly airflows are normally healthy and southerly flows unhealthy.

Over more than a year of observation, I have found a distinct pattern in how those polluted airmasses come to impair Kingstonians’ health.  More often than not, 50% or more of the southeasterly quarter of North America (below and to the east of the Great Lakes) is enveloped by Level-2 fine particulate matter (i.e., yellow shading denotes PM2.5 concentrations of 12 µg/m3 or higher).  The prevailing flow of those unhealthy airmasses is northeast from Texas and Louisiana, across the Appalachians and out over the Atlantic Ocean, driven by mostly southerly wind directions.

The succession of three US EPA AirNow map extracts below show a typical development cycle for the chronically polluted airmass, in this case from November 22 through 25, 2024. This cycle, of varying intensity, unfolds almost weekly year-round, with differing details driven each time by regional wind intensity and directions.  Canadian PM2.5 levels are not shown in the maps because the EPA cuts off its forecasts at the border. About half the time, and almost always when Eastern Ontario is experiencing northery winds, we get lucky with the airmass moving out over the Atlantic without spilling over our area. When those winds are blowing from the south, however, the pollution comes our way.

The key observation from this repeating cycle which helps to identify the causes is that the pattern usually begins with yellow-shaded Level-2 concentrations building up around Houston, Dallas and New Orleans.  Those centres happen to be where the majority of US petroleum refineries are located.  Given that refineries operate almost continuously and are prodigious emitters of PM2.5 particulates along with many other toxic airborne pollutants, they are likely the primary source of Kingston’s worse-than-the-WHO-limit PM2.5 levels.  

Lest we simply blame the Americans for the resulting excess mortality and lung disease which those emissions cause in our community, it is worth noting that almost all of Canada’s oil-sands crude production is sold and shipped to the US for refining.  We shouldn’t be surprised that some proportion of that production comes back to afflict Canadian lungs.