Simulation of pollen–humidity interactions and origin of airborne sub-pollen particles

Airborne pollen can break down into sub-pollen particles (SPPs) due to osmotic forces, which can penetrate deep into the respiratory system, triggering heightened allergic responses. This study aimed to simulate pollen-humidity interactions for several pollen types including Golden wattle (Acacia Pycnantha), Perennial Ryegrass (Lolium Perenne) and Insignis pine (Pinus Radiata) using a novel experimental setup featuring a rotating drum for incubating airborne pollen at different humidity levels. An assortment of aerosol instrumentation and characterisation methods were used to study the aerosols inside the drum. SPP formation, ranging from 0.15 to 5 μm, was observed in Perennial Ryegrass at high levels of 95 % and 99 % relative humidity (RH). Notably, evidence of SPP formation in Golden wattle at 99 % RH was revealed for the first time, with their sizes ranging from 0.18 to 5 μm. These observations indicate a species-specific response to varying humidity conditions and lay the foundation for assessing the allergic potential of various species across Australia. In summary, high RH levels therefore have the potential to generate SPPs in both Golden wattle and Ryegrass. Additionally, the experimental setup, techniques, and instrumentation presented herein can support future studies assessing the isolated influence of meteorological parameters on airborne pollen.