1. The growing awareness of the health impacts of airborne particulate matter (PM) and the limitations of regulatory monitoring networks have catalyzed interest in low-cost particulate matter sensors (LCPMS). While optical sensors dominate the market, their accuracy is limited by factors such as particle shape, density, and surface contamination. This work presents the QCM4PM, a novel QCM-D (Quartz Crystal Microbalance with Dissipation) based device, as a compelling alternative. Capable of measuring both mass and viscoelastic properties of particles, it represents a promising approach for real-time, filter-free PM monitoring. Preliminary results show that QCM4PM provides stable and sensitive detection of PM2.5, potentially enhancing IoT-enabled air quality networks.