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Dustfall Monitoring

What is Dustfall and why is it important?

Dust refers to solid particles in the air, but there is an important distinction between the fraction of particles that quickly fall out of the air (dustfall), and the portion that remains airborne (particulate matter) at any given point.  Once dust is generated, it will spread out from the source and be carried on the wind away from the site.  The impacts of dust will decrease with distance, as the larger dust particles will deposit almost immediately and relatively close to the source.  Finer particles tend to fall out of the air after a further time and distance.

PRPA actively measures the concentration of the smallest particles (PM10 and PM2.5) that tend to stay in the air the longest.  The effects of these small airborne particles are associated with impact on human health.  

How is Dustfall measured?

PRPA supplements the particulate monitors with eight dustfall stations at the Westview terminal site boundaries.  The effects of dustfall are usually associated with nuisance factors, primarily with its capacity to soil surfaces (e.g., a car, window sill, buildings, etc.).  Depending on its concentration and composition, it could also have an impact on soils and vegetation.

Dustfall is monitored through the use of canisters that collect dustfall over periods of time and can be both measured and analyzed for its composition when required. The standard monitoring period is one month, and spot samples are collected on an ad hoc basis.

Dustfall monitoring can be limited by the difficulty in establishing singular events that may influence the monitoring period, and by the variety of sources that can influence any given sample.  Even in close proximity to an industrial activity, dustfall measures are significantly impacted by weather, wind direction, and other community sources such as road dust, diesel emissions, pollen, insect parts, and residential wood smoke/open burning emissions.  For this reason, weather data, visual observances and neighbourhood feedback are extremely important supplements to dustfall monitors.

How much Dustfall is acceptable?

The British Columbia Ministry of Environment has established dustfall objectives that inform regulatory development and air management efforts.  These objectives have been adopted by PRPA with respect to dustfall.

Dustfall: 1.7 milligrams per square decimeter per day, averaged over a 1 month period

 

Measurements recorded by the Prince Rupert Port Authority — September 2016

SITE

1

2

3

4

Monthly Average (mg/dm2/day)

0.20

0.20

0.17

0.57

Fixed (non-organic)

0.03

0.06

0.11

0.00

Volatile (organic)

0.17

0.14

0.06

0.12

Species

%

#

%

#

%

#

%

#

Pollen

10%

0.02

5%

0.01

10%

0.01

10%

0.01

Other Plant Material

30%

0.06

20%

0.04

40%

0.06

40%

0.04

Insect Parts

5%

0.01

40%

0.08

20%

0.03

30%

0.03

Wood Pieces

30%

0.06

5%

0.01

0%

0.00

0%

0.00

Other Dust

25%

0.05

30%

0.06

30%

0.05

20%

0.024

Total

100%

0.2

100%

0.2

100%

0.15

100%

0.1