CROFTON MILL AIR POLLUTION DEPOSITION CONTROL FACTORS
I was requested by Tammy Morris to provide a short statement regarding
air pollution deposition control factors in the vicinity of the
NorskeCanada pulp mill at Crofton, B.C.
My background as a meteorologist who has worked in the area for the
past 28 years (Officer in Charge of the Victoria Weather office from
1975 to 1991), and as a flight instructor for the past seven years, has
given me a unique perspective of the air pollution problem at
Crofton. Much of the flight training is carried out in the
Duncan, Crofton, Chemainus area, which has given me an opportunity to
observe mill effluent in all seasons and weather conditions.
Types of Air Pollution
Industrial air pollution from mills, such as the one at Crofton fall, into two basic categories: particulate and gaseous.
Particulates include such things as carbon and ash, which gradually
fall from the smoke plumb downwind from the source. The higher
the effective release point and the stronger the wind the further these
particulates can be carried before they are deposited on the ground,
therefore reducing their concentration.
Gaseous pollutants include such things as sulphur dioxide and nitrous
oxide to name a few, which do not precipitate by themselves, but often
mix with falling precipitation (rain or snow) to produce such things as
acid rain, often at a great distance from the pollution source.
It goes without saying that the better the filtering and scrubbing of
the effluent, the fewer the pollutants that reach the air in the first
place. But, it is also true that the wider the area of dispersal
due to strong winds and higher effective injection point (higher stack
or better ventilation), the less the concentration at any given point
on the ground. As they say “the solution to pollution is dilution”.
Wind Circulation Patterns Influencing Pollution Dispersion
The best conditions for dispersing air pollutants are a combination of
strong winds and unstable air (higher effective injection point).
This frequently happens with approaching weather disturbances resulting
in strong south easterly winds in the Strait of Georgia and Stewart
Channel past the mill.
The poorest conditions occur with light winds and a thermal inversion,
where the temperature in the lower part of the atmosphere increases
with height As a result, pollutants are not carried very far from
the source, and the effective ejection point is low because the plumb
cannot be carried aloft due to the stable air. These conditions
occur frequently in the summer and fall when a high pressure area
dominates the region, resulting in fair weather, but also stagnant
conditions with light winds and a thermal inversion. During
situations in the spring and summer when the inversion is not too
intense, strong surface heating by the sun can break the inversion,
resulting in good ventilation during the afternoon period. This
will usually result in coastal sea breeze developing as well, which
will carry the plumb off to the west from the plant.
Another local factor can exasperate the pollution problem during over
night periods. On clear nights when winds are light, cold air
drains down the relatively high mountains surrounding Cowichan
Lake. This cold air collects over Cowichan Lake and then drains
down the 500 foot slope of the Cowichan Valley toward the coast.
This colder air under-cuts the warmer air near the ground over Duncan
and Crofton areas, increasing the strength of the inversion and as a
result makes the pollution problem worse during the morning hours.
Definition of the Crofton Airshed
My definition of the Crofton airshed would be: That area
surrounding the Crofton Mill where pollutants known to have been
injected into the atmosphere from the mill are deposited on the ground
or in the water in measurable quantities.
As for the boundaries of the Crofton airshed (based on my definition),
it is impossible to define accurately without some scientific data from
a sampling network. But my guess is that it would probably extend
from Central Saanich, across much of Saltspring Island to Nanaimo
Airport, back along the island mountains west of Ladysmith and
Chemainus, then southward across Duncan to Shawnigan Lake.
Recommendations for Further Action
If your citizen’s group in unsuccessful in forestalling the fuel
testing at the Crofton Mill, I would strongly suggest getting the
provincial environment group involved, or perhaps Environment
Canada. To do a proper evaluation of the fuel tests, the effluent
should be sampled and analyzed for content. Ideally an array of
air quality monitoring and wind detection stations should be set up and
at various distances and directions from the source and the collected
pollutants should be analyzed for content. There should also be a
daily statement of atmospheric factors such as airflow pattern,
ventilation index and local effects, in order to help correlate the
pollution patterns.
I hope this helps.
Norm Dressler
Meteorologist
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