Accuracy of a hand-held resistance-free flowmeters for flow adjustments of Hirst-Type pollen traps

AbstractThe Hirst-type pollen trap (1952) is the most common device for aerobiological measurements of pollen and fungal spores in ambient air. In the 1960s the in-line flowmeter was removed and studies since then showed considerable variability in the airflow pumped through the instrument when using hand-held rotameters with an internal airflow resistance to adjust flowrates. To avoid this problem, our study compared the variability of airflow rates of Hirst-type traps when using commercially-available low-resistance airflow meters (heat anemometers) at various timescales. Experiments were conducted in Munich (Germany) and Payerne (Switzerland), using 4 different easyFlux ® instruments and 6 Hirst-type pollen traps. Measurements were taken on an hourly basis from dawn to dusk at both locations, and in addition at Payerne, weekly observations over a period of one year. When using the common hand-held rotameters (with airflow resistance) the flow was 28.3% lower than with resistance-free flowmeter (i.e., measured 10 L/min which was in reality 12.8 L/min). The coefficient of variation between the four easyFlux® devices ranged from 0.32% to 1.55% over one day and from 2.88% to 8.17% over an entire year. Some of the traps showed surprising flow variations during t he day. Furthermore, flowrates deviated more when measurements were made at the point where the double-sided tape is behind the orifice than elsewhere on the drum. The measurements away from this point are representat...
Source: Aerobiologia - Category: Environmental Health Source Type: research