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The pollen count starts on the roof of the hospital with a Burkard Volumetric Spore Trap (pictured on the right). Air is sucked through a hole at a specific rate into the head of the machine where it passes over a tape that is coated in wax. Anything that is floating around in the air is also sucked into the machine and sticks to the tape as it passed through the machine.
After 24 hours the tape is taken out of the machine and replaced with a new tape to collect pollen for the next 24 hours.
With the tape out of the machine it is trimmed and mounted onto a microscope slide, we use a stain to make the pollen grains stand out.
The slide is then examined under a microscope at 40 times magnification, this lets us look at a section of the tape that is 0.55mm in diameter.
The slide is moved under the microscope so that 12 sections of the tape, each measuring 0.55mm x 18mm, are examined. As the tape passes through the viewfinder each pollen is identified and counted.
After all 12 sections have been counted, the total number of pollens counted for each species are added together. So, now we know how many pollen grains have been collected on a specific amount of the tape, and we know how much air has passed over the tape, so we perform some calculations to work out the amount of pollen grains in a cubic meter of air, averaged over a 24-hour period.
When you see the pollen forecast it is based on data collected using this method over many years.