First Experiences with Low Cost Optical Particle Counters Reveal Spore Emission in Woodlands During Night Time

Background: Monitoring of spores with traps of the Hirst design is labour intensive. A new generation of fully automated, but expensive (>100,000€), systems (e.g. WIBS or Rapid-E) has potential to replace the Hirst trap and can deliver data in real time. When studies require multiple locations with high temporal resolution an alternative approach is therefore needed. The purpose of this study is to evaluate a low cost (~260€) particle counter for real time observations of spores with high temporal resolution. Methods: Three modified low-cost mobile real-time particle counters were placed 1 m above a known source of fungal spores in a woodland near to Worcester in autumn 2017. A Burkard trap and a data logger were placed near the particle counters. Slides from the Burkard trap were analysed with respect to the dominating spores found during the campaign. Data from the particle counter, available every 10 sec in 16 different size bins, have been aggregated to hourly intervals comparable to data from the Burkard trap. Results: The spore counts (Burkard trap) show high night time concentrations of spores relating to the known source and no spores of this type were observed during the day. The results from the particle counter were highly correlated with spore counts, e.g. ascospores found in the size range 12-14um during night-time and nothing during day-time. Data from the weather logger shows that night-time peak concentrations were only found during long periods when relative humidity reached 100%, thus identifying a primary emission process. Discussion & conclusion: The application of a real time particle counter has been used here to demonstrate how processes of spore emissions can be revealed in the real time using low cost equipment. Care must however be taken as they only detect size and not composition. Nevertheless the devices have substantial potential to supplement existing monitoring networks, as personal devices or within process based studies.