Annual,daily and diurnal variation of Urticaceae pollen in North-central London

Summary Annual differences in cumulative counts of Urticaceae pollen are found to relate primarily to the weather conditions during the pollen formative period (April and May) and secondarily to the weather prevailing during the season itself. Relative humidity, temperature, wind velocity and precipitation emerge as the most influential variables in the analysis of daily variations but their relative importance varies between years. Diurnal patterns in concentrations show general peaks occurring in the early evening but the severity and exact timing of these relates closely to wind direction. The implications of these results are considered in the context of forecasting.