The Incidence of Increases Pollen Concentrations During Rainfall in the Air of London

Data from a Burkard volumetric sampler in a densely built-up area of North-central London, England are used to investigate the effects of rainfall on pollen concentrations over four years. Pollen counts generally decreased with rainfall, although several episodes of increased pollen concentration have been recorded in London following the onset of precipitation.
Pollen concentration is recorded as two-hourly pollen counts, while hourly records of nine meteorological variables, including rainfall amount and intensity, are obtained from the London site of the Meteorological Office. The two-hourly changes in concentration that take place during both «normal» rainfall events and during those displaying marked increases in pollen concentration are examined in relation to the patterns of rainfall, the wind regimes, synoptic situation and general characteristics of urban areas.
The influence of rainfall in removing pollen from the air is also examined in relation to the rainfall intensity and size of pollen grains for selected taxa.