Methodology
Pollen traps and their function
Each station is equipped with a Burkard pollen trap, which collects the pollen count using an internationally standardised method.
How does the pollen trap work?
The air with all the microparticles it contains (pollen, spores, inorganic particles, etc.) is sucked in by a vacuum pump inside the pollen trap. A constant volume of 10 litres of air per minute passes through a suction slot onto a drum that carries a Vaseline-coated film strip. A wind vane ensures that the suction slot is always exposed to the current wind direction. A small umbrella above the slot protects against rain.
The drum rotates at a speed of 2 mm/hour. The pollen grains and other microparticles contained in the air stick to the adhesive film. The drum must be replaced and the movement wound up after one week at the latest.
Preparation and microscopy
The film strip is now divided into daily sections, embedded in water-soluble plastic, "Gelvatol", with the addition of a colouring agent (Safranin) and examined for pollen under a light microscope at 400x magnification. Four lanes are analysed per slide. This makes it possible to determine the position and number of individual particles to within two hours.
The resulting number of pollen grains does not directly give the number of pollen/m3 of air; this must be calculated using a formula.
The trap draws in 10 litres of air per minute, which results in 14.4m3 of air per day. The pollen contained in this amount of air is deposited on the entire film with an area of 672 mm2 (14 x 48 mm). If four lanes are counted and the diameter of the field of view in the lens is known, it is possible to transfer the collected number of pollen grains proportionally to the entire area.
In order for the collected data to be statistically analysable, the examined area must not be less than 10-12 % of the total area of the film.
For example:
- 4 lanes were analysed
- Counted pollen grains: 360
- Field of view of the microscope at 400x magnification: 0.45 mm
- Air volume sucked in: 10 l/min; 14.4 m³/day
1. examined area:
Diameter of the field of view x length of a horizontal path x number of paths
0.45mm x 48mm x 4 = 86.4 mm2
2. ratio between total and examined area:
672mm2/86.4mm2 = 7.78
3. convert the counted amount of pollen to pollen/m3 air.
7.78 x 360/14.4 = 194 pollen/m3air
