On the efficiency and correction of vertically oriented blunt bioaerosol samplers in moving air

Abstract

The aspiration efficiency of vertical and wind-oriented Air-O-Cell samplers was investigated in a field study using the pollen of hazel, sweet chestnut and birch. Collected pollen numbers were compared to measurements of a Hirst-type Burkard spore trap. The discrepancy between pollen counts is substantial in the case of vertical orientation. The results indicate a strong influence of wind velocity and inlet orientation relative to the freestream on the aspiration efficiency. Various studies reported on inertial effects on aerosol motion as function of wind velocity. The measurements were compared to a physically based model for the limited case of vertical blunt samplers. Additionally, a simple linear model based on pollen counts and wind velocity was developed. Both correction models notably reduce the error of vertically oriented samplers, whereas only the physically based model can be used on independent datasets. The study also addressed the precision error of the instruments used, which was substantial for both sampler types.

Modelled and observed surface soil pollen deposition distance curves for isolated trees of Carpinus betulus, Cedrus atlantica, Juglans nigra and Platanus acerifolia

“…The second criteria was for the sampling surface to have been consistently managed over the previous few years. Finally, the trees needed to stand where an open sampling distance of 100m could be accessed along the prevailing wind direction of the previous pollination period (Michel et al 2010(Michel et al , 2012. In addition, it was also desirable to look at trees that are not common or widespread in the UK, ensuring that observed pollen can be attributed to only localized sources (Sommer et al 2015).…”

Relative efficiencies of the Burkard 7-Day, Rotorod and Burkard Personal samplers for Poaceae and Urticaceae pollen under field conditions

“…Given that 7-Day sampler efficiency is thought to be largely invariant over the majority of this interval, it seems appropriate to attribute this decline to a reduction in PVAS efficiency. Qualitatively equivalent results have been obtained for a vertically-orientated Air-O-Cell for birch pollen (22 µm), although relative concentrations were far lower due to the effect of the Air-O-Cell's sharp inlet on local airflow [43].…”

“…Although the RMSEs for these conversions are not small, ranging from 29-47%, we would not expect two identical samplers standing next to one another to record the same concentration. The RMSE between the collector rod pairs in the Urticaceae study (difference scaled by mean) was 12.73%, while for birch pollen RMSEs of 38% and 57% have been reported, respectively, for pairs of 7-Day samplers and vertically-orientated Air-O-Cell samplers mounted in a compact array [43]. The errors associated with the corrections presented in the current study are therefore acceptable when compared with the precision errors of the individual instruments.…”

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

“…Observed distribution of the pollen grains across the width of the impaction surface corresponded to what is commonly seen in the case of Hirst-type trap. We observed both convex (Tormo Molina et al 1996;Michel et al 2012) and concave (Cotos-Yanez et al 2013) distribution in the analyzed samples. The distribution of particles over the slide width is determined by the effect that construction of the device has on the air flow.…”