We collect the UK pollen data using a network of pollen monitoring stations run by the Met Office. The stations all use the same type of device, the seven-day volumetric spore trap made by Burkard. Most stations are located on flat roofs of two or three storey buildings. Collecting pollen from the ambient air on rooftops avoids measuring highly localized pollen concentrations.
Each trap has a pump that pulls air through a slit-like orifice at a rate of 16 litres per minute. The pump contains a rotating drum mounted with sticky tape that traps pollen, spores and other airborne particles. The drum uses a clockwork mechanism to revolve past the orifice at a rate of 2mm per hour. After 7 days, we cut the tape into 24-hour lengths and then mount these strips onto microscope slides.
The slides can then be counted for pollen (and other bioaerosols) which are identified by family, genus or species. To obtain the classic pollen count, we rotate the tape 12 times every 2 hours. We convert these 2-hourly readings into daily average pollen count by calculating the pollen grains per cubic metre of air.