If you're building an air quality monitoring app, integrating IoT sensors, or designing smart building dashboards - you've probably come across the term HEPA filter. But do you know what's actually happening at the physics level? And more importantly, how does it affect the data your sensors report? This article breaks down HEPA filter mechanics from a developer's perspective, shows you how to read PM2.5 sensor data in Python, and explains why commercial-grade HEPA systems (like those inside modern automatic hand dryers) are becoming a data source worth integrating into your indoor air quality apps. What Is a HEPA Filter, Really? HEPA stands for High-Efficiency Particulate Air. It's not a brand - it's a performance standard. To qualify as a true HEPA filter, a filtration medium must capture 99.97% of particles at 0.3 micrometers (µm) in diameter. Why 0.3µm specifically? Because that's the Most Penetrating Particle Size (MPPS) - the size that's hardest to trap.…