AberTrap: an open-source, lightweight, programmable sampler of airborne biological particles
1. Context. Capturing and identifying airborne biological matter (bioaerosols) enables detailed characterisation of ecological communities, but the cost and weight of existing commercially available active air samplers limits the deployment of multiple devices needed to realise this potential. 2. Method. We present the AberTrap, a lightweight (~50g), open-source (CC-BY-SA), programmable rotating-arm bioaerosol sampler that can be self-built from common laboratory components and makerspace equipment at low cost (ca {pound}20 per unit, exc. power supply). To characterise the device's performance, we first explored the influence of rotational speed and paddle design on aerosol capture under controlled conditions, using fluorescein and a range of biological aerosols (4.5-33 m). To demonstrate its utility for ecological applications, we then validated field performance in a species-rich broadleaf woodland (England, UK), deploying eight samplers over five days and identifying captured fungal aerosols by ITS2 metabarcoding. 3. Key results. Modifying paddle design allowed us to influence particle selection and capture efficiency. Slotted paddles captured significantly more aerosols than plain paddles despite sampling less air, which we traced to the concentration of aerosols at the paddle leading edges. This effect was most pronounced for the smallest particles and outweighs the influence of rotational speed. In the field, 20 daily samples (four samplers over five days) detected 2,431 fungal taxa, 78.9% of the Chao2-estimated total fungal richness. A single sampler captured only 59% of this richness. Continuous 5-day sampling recovered 78% of the taxa detected by daily sampling, indicating only modest paddle saturation over this period. Our time segregated design allowed us to infer dispersal dynamics; 35% of taxa were recorded only on one day, and 19% recorded across all five days. Overall, replicate AberTraps provided high sampling completeness. 4. Implications. The AberTrap provides a low-cost, lightweight and programmable alternative to commercial rotating-arm samplers, enabling levels of spatial and temporal replication impractical with existing devices. Low cost and portability facilitate deployment in remote or resource-limited contexts. Its open-source, adaptable design allows the device to be tailored for applications in biodiversity assessment, pathogen surveillance and ecological monitoring.