Pollen is measured in terms of a pollen count. A high pollen count number indicates a high pollen density in the air. Pollen can come from weeds, grass and trees. The Rotorod sampler is the device that is most commonly used to obtain pollen measurements.

Set up the Rotorod sampler according to the manufacturer’s directions. The device is typically placed on an accessible rooftop. Set the sampling period to a 10 per cent duty cycle which allows the unit to run for one minute and then turn off for nine minutes throughout a 24-hour period.

Collect the acrylic rods from the Rotorod sampler and place into a rod holder.

Stain the rod with Calberla’s stain through a pipette. Once the rods are covered with stain, place a 22-by-22-millimeter glass cover slip lengthwise over each rod.

Allow the pollen to absorb the stain for 15 to 20 minutes.

Examine the rods individually using a light microscope under 400-times magnification.

Place a counting reticle into the eyepiece of the microscope. This glass disk contains a grid that helps to measure pollen size and aids in keeping track while counting the pollen.

Count the pollen grains present on the rod and record the number.

Determine the amount of pollen grains per cubic millimetre by using the following equation:

(Number of grains counted / 33.44 mm2)* 100

Convert the number of pollen grains from cubic millimetres to cubic meters. Take the value derived from the above equation and divide by 1,000 to obtain the pollen count in cubic meters.

Repeat steps 7 through 9 on the second rod.

Add the pollen count numbers from each rod together and divide by two to obtain the average pollen count.

### Things you need

- Rotorod sampler
- Calberla’s stain
- Rod holder
- Pipette
- Two glass cover slips (22 by 22 millimetres)
- Light microscope
- Counting reticle

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