Thread by @linseymarr

Real-world test of ionization in a campus building. We did not see a reduction in particle number concentrations at supply vent when system was on vs. off, measured using TSI Aerotrak. /1

Thanks to @VTFacilities for suggesting this and providing access. Photo shows the ionization unit in blue inside the HVAC duct. /2

@ajprussin and David Kormos took turns holding the particle counter at the supply vent. /3

Concentrations were actually 2, 8, 13, 4, 4, 111% higher (by size bin, p = 0.01, 0.00, 0.08, 0.84, 0.88, 0.17) when ionization unit was on, but we necessarily did this sequentially in time, so it's not a perfect comparison. /4

I handled ozone measurements with Thermo 49C (not recently calibrated). It was 28 ppb outside and 10 ppb in the classroom, so not a problem. /5

This was just one set of measurements at one point in time, but I'd say there's no way the ionization system is reducing particle concentrations by 90% or more in this real-world application. Ionization does work in electrostatic precipitators with collection plates. /6