by Dave Stevens and Delores Broten
There is good reason to doubt that anyone in Canada has a solid handle on how much air pollution Canadians are exposed to.
Pollution data comes mainly from two sources, self-reports by the polluters, published in the NationalPollutant Release Inventory (NPRI) and ambient (outdoor) measurements taken by firms and governments.
Ambient air pollution monitors are located where the pollution they assess is, to some degree, representative of what people will breathe. In Smithers BC, where I live, the particulate matter (PM) monitors are co-located with St. Joseph’s School in the middle of town. This is a common situation in BC. Data from these monitors is collected on an hourly basis, reported to a central database maintained by the Ministry of Environment (MoE) in Victoria and available online. One very common monitor is a type of continuous device called a TEOM, a Tapered Element Oscillating Microbalance.
The basic idea behind a TEOM is that pollution particles (particulate matter, or PM) are drawn through an opening into the machine and their size is measured. The size of the opening determines how big the particles are, so a 2.5 micron opening is used to measure a certain size of very small particles, called PM2.5. A ten micron hole would be used in measuring PM10.
The readings are micrograms of PM, either PM2.5 or PM10, per cubic metre of air. A common sort of reading is that taken this morning in Smithers at 9AM of 16 micrograms (µg/m3) of PM2.5. Not enough to kill you outright (for most people) but not a healthy level either.
A great deal of public health work has been done on the health effects of PM and while the subject is too large to tackle here, it is certainly clear that there is no minimum level of PM below which there are no health effects. There’s no threshold of safety: if you can detect it, it hurts you. And the more there is, the worse and the more immediate the effects are. The Canada Wide Standard settled on by the Canadian Council of Ministers of Environment aimed for levels of PM 2.5 of no more than 30 μg/m3, 24 hour averaging time, to be in effect by this year, 2010. It also stated that recent scientific evidence indicated that “there is no apparent lower threshold for the effects …on human health.”
So the question of just how much pollution we are breathing is not at all theoretical – it matters a lot whether the readings are correct and current.
But are they? Not necessarily
Winter often has the highest pollution levels. Cold air tends to produce atmospheric inversions that trap and concentrate pollution near the ground. Levels in Smithers last year in January reached 165 for PM10 and 65 for PM2.5. These figures are not exceptional for the place and time of year.
Now, measuring instruments always have limitations, and it is necessary to take the characteristics of the gear into account in deciding what to make of the data. In an attempt to provide stable conditions for reliable measurement, the manufacturers of the TEOMs warm the inlet air in cold weather. And that turns out to be a problem.
Smoke emitted in cold weather contains volatiles that form particles. But when these airborne particles pass through the warmed inlet pipe they partly re-evaporate and fail to deposit on the microbalance. They become immeasurable.
BC MoE staff estimate that in cold weather the TEOMs routinely underestimate PM levels by as much as 50%. So the peak levels in Smithers referred to above might have been up to 300 for PM10 and 130 for PM2.5. These levels are about half of what is estimated for the infamous London smog epidemic of 1954 which killed 4,000 people immediately and another 8,000 with subsequent infections. Nonetheless, they are still a long way from desirable.
What is to be done?
BC has already begun to replace the province’s monitoring equipment. This offers the prospect of more accurate measurements. To look at the differences in measurements, some of the new equipment is running in parallel with the older TEOMs. This promises to be useful to evaluate data gathered by the network in years past.
The data from the new gear is likely to be quite bad news.
Part of the Canada-Wide Standards for PM and Ozone is the Guidance Document on Achievement Determination. This sets out the method of determining whether a given place exceeds the 30 µg/m³ national standard. But of course it relies on the accuracy of the measurements.
The BC Lung Association’s 2009 State of the Air report shows, “The highest concentrations were observed in the central interior (e.g. Quesnel and Prince George) and Bulkley Valley (e.g. Houston and Smithers). Daily values ranged from 8-26 μg/m3 (based on annual 98th percentile).” But those values are based on the old equipment. If the levels were actually 16-52 we have quite a different picture. Areas that were thought to be ok by provincial or national standards will now be sometimes out of attainment, and worse health effects are to be expected.
How will government and industry react? A rational, precautionary approach indicates that more protective measures will be taken. Permit holders formerly thought to be operating safely will now be revealed as contributing excessively to health risks for those nearby. Unfortunately, the BC government commonly conceives of its role as handmaiden to industry, making deals and providing breaks to make industry in BC more “competitive.” An added “regulatory burden” will not be viewed favourably by these partners.
It is standard advice from government and health authorities during pollution episodes to go inside and sit quietly. Some highly vocal outrage is likely to be a more productive course.
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Dave Stevens is a self-employed computer geek and amateur carpenter. From time to time he advises Environment Canada on how to handle toxic emissions. They don’t take the advice but they pay anyway.
