Analysis of airborne pollen time series originating from Hirst-type volumetric samplers—comparison between mobile sampling head oriented toward wind direction and fixed sampling head with two-layered inlet

In this study, we have compared time series of pollen concentration originating from two Hirst-type volumetric samplers that were equipped with different sampling heads. To collect airborne pollen, we have used classic sampler with mobile sampling head including wind vane and adapted sampler with fixed sampling head having two-layered inlet, like in Sigma-2 passive sampler. The devices were placed at the roof level, on the top of the building of the Faculty of Sciences located in Novi Sad, Serbia. The sampling of airborne pollen was performed from February until October 2019. Along with the pollen data, meteorological conditions were recorded with an automated weather station measuring solar radiation, air temperature, relative humidity, wind speed and precipitation. Time series of daily pollen concentrations expressed high correlations, although there were large differences on the hourly basis. Absolute difference between hourly values showed very weak correlation with relevant meteorological parameters: temperature, humidity, precipitation, wind speed and turbulent kinetic energy, leading to the conclusion that sampling with both heads was not affected by meteorological conditions. Counting the pollen grains from the whole sample and not just from 10% of the area, which is the minimum requirement, was done for the six days in the season and proved that error introduced by subsampling during analysis was the main reason for differences in time series. To conclude, replacing mobile sampling head with fixed sampling head having two-layered inlet does not notably affect the quantity of pollen recorded by the Hirst-type volumetric method.