Heather and Bruce Andersen live in Bloomer, Wisconsin, and want to setup a MiniVol to identify dust from nearby mines. @gretchengehrke, @stevie, and I set out to do a site survey, following the activity, Identifying a PM monitoring site for deploying a MiniVol.
Bruce had already driven a pole into the ground in the center of their largest clearing for test deployments of passive PM monitors. We proceeded to check if that point met the siting requirements.
- Measuring tape (we used a surveying tape because of distances greater than 20m (65'))
- Camera or phone camera (taking panoramas is helpful)
Is there a 270° arc of unrestricted airflow to the suspected dust source (the mine) along the predominant seasonal wind direction?
Determining predominant wind direction
Using Windhistory.com we determined that Rice Lake Airport, 30 miles north, was the closest NOAA weather station. Most prevailing winds through the fall to early spring are from 120°-140° SE, but the second most common direction is 260°-330° out of the West and WNW, the same direction as three different mines within 3 miles.
It doesn't appear that the mines are upwind very often during the late spring, summer, and early fall, but this wind data is from 30 miles away.
Photographing the site and determining direction and distance
Together we took bearings and measured distances to nearby obstacles using the compass, surveying tape, and cameras.
Our goal was to determine if our location met the following criteria:
- 2-7 meters (6'7" - 23') above ground level
- at least 30cm (12") from any obstacle to air flow.
- at least 2 meters (6'7") from walls and architectural features
- at least 5 meters from natural gas combustion flues
- away from fuel oil, coal, or solid waste incineration
- at a distance at least twice as far away as the heights of the nearest obstacle that protrudes above the sampler.
- at least 20 meters from the dripline of the nearest tree. If trees are unavoidable, at least 10 meters from the nearest tree with the tree as a noted obstruction
criteria 1 was met by mounting the MiniVol at the top of the 48" pole. The MiniVol and its mounting bracket added 36", and required 4" of the pole for mounting, for an aggregate inlet height of 79" (6'7", sightly more than 2m).
Criteria 2-6 were met, but several trees appeared to be within 20 meters (65'7"). We took out our survey tape and measured them out in feet. All our long measuring tapes are in feet, not meters.
This annotated panorama shows the various compass directions in context, and the distances in feet to different obstacles:
Several small trees were within 20m (65'7"), however none were closer than 10m (32'10"), and those that were are very short.
Can we place a second air inlet for the field blank?
@GretchenGerhke's review of MiniVol research suggests we should deploy a second filter as a field blank-- a sample exposed to the same conditions without having air pumped through it. The MiniVol's inlet can't be airtight, and a certain quantity of dust will fall in during setup and operation. The field blank will allow us to discount the effect of these unwanted particles.
Bruce and Heather suggested that we deploy the MiniVol's second inlet and impactor assembly on the ground pole. Ideas for covering the bottom of the impactor assembly were: cling wrap (a favorite), a rubber banded plastic bag, or a dowel. Bruce had a 1" dowel. With some sanding the dowel was press-fit into the impactor assembly, allowing the asssembly to be joined to the pole. In keeping with the rule that the inlet should be at least 30cm from an obstacle to airflow, we put it below and to the SE ,at 56". (criteria 3)
- We are concerned that the sample blank may be too low at 56" rather than 79" (~2m)
- Our wind and weather data is from 30 miles away. Bruce and Heather are considering purchasing a weather station and recording their local weather.