Automated Microscopy Techniques On Passively Collected Samples Provide Reliable Quantitative Data On Airborne Pollen

Data on airborne particles are critical to protecthuman health. Anthropogenic (e.g., soot, and tire and brake wear) as well as biogenic (e.g., pollen and spores) particles are usually monitored by active samplers located in urban environments; thus, very few data are available for remote, mountainous areas. In addition, bioaerosol analysis is time-consuming and skill-intensive. Hence, to avoid the obstacles of active sampling (i.e., the high cost and power consumption) and simplify data analysis, we investigated passive sampling combined with automated analysis as a method for pollen detection. We deployed two Sigma-2 passive samplers for 12 week-long periods during 2018 in San Michele all'Adige, Italy, where airborne pollen has been monitored by a volumetric Hirst-type sampler since 1990. To obtain the morpho-chemical information of single particles, we then analyzed the samples using (i) automated optical microscopy (OM) followed by image analysis based on the particle sizes and grey values, and (ii) automated scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX). The automated OM detected bright particles (i.e., from natural sources) in the size range of 20-80 mu m, which accurately represented the total pollen, and the SEM/EDX filtered the particles by size, shape and chemical composition, which enabled us to identify the likely pollen candidates (the "pollen-like" fraction). Overall, automated analytical techniques can concurrently provide data on airborne anthropogenic, geogenic and biogenic particles, including pollen. Furthermore, passive sampling offers a reliable option for collecting data in aerobiological studies, especially in remote areas, where maintaining active samplers is challenging.